ABSTRACTS OF CURRENT TECHNICAL LITERATURE IN ELECTRICAL ENGINEERING
CONTENTS
1.1 ELECTRICAL MACHINES
1.2 ELECTRICAL MOTORS & DRIVES
1. ELECTRICAL MACHINES : MOTORS & DRIVES
38293
Zhaoping Xu & Siqin Chang
Improved Moving Coil Electric Machine for Internal Combustion Linear Generator
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 281 – 286
This paper investigates the use of moving coil linear machines (MCLM) in the internal combustion linear generator (ICLG), which is a novel solution for series hybrid electric vehicles, distributed generation, and emergency power supply. According to the analysis of the basic structure of MCLM, an improved tubular MCLM equipped with quasi-Halbach magnetized magnets is suggested and analyzed with a proposed equivalent magnetic circuit (EMC) model. Measurements on a 4-kN prototype show good agreement with the results from the EMC model. Compared with the reported moving magnet linear machines (MMLM) for the same application, the proposed machine has the merit of less moving mass, faster response, and better controllability.
38294
Chen J.T.& Zhu Z.Q.
Winding Configurations and Optimal Stator and Rotor Pole Combination of Flux-Switching PM Brushless AC Machines
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 293 – 302
A simple analytical method is developed to compare the combinations of stator and rotor pole numbers in flux-switching permanent magnet (PM) machines in terms of back electromotive force (EMF) and electromagnetic torque. The winding connections and winding factors of machines having all poles and alternate poles wound, and different numbers of phases, from two to six, are determined by the coil-EMF vectors. Their differences from analyzing the conventional fractional-slot PM machines with concentrated nonoverlapping windings are highlighted. The general conditions are established for balanced symmetrical back-EMF waveform. It shows that the optimized rotor pole number should be close to the number of stator poles, whereas larger torque can be obtained by the machine with relatively higher rotor pole number. The analysis is validated by finite-element analyses and experiment.
38295
Espinosa A.G.et.al
Fault Detection by Means of Hilbert–Huang Transform of the Stator Current in a PMSM With Demagnetization
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 312 – 318
This paper presents a novel method to diagnose demagnetization in permanent-magnet synchronous motor (PMSM). Simulations have been performed by 2-D finite-element analysis in order to determine the current spectrum and the magnetic flux distribution due to this failure. The diagnostic just based on motor current signature analysis can be confused by eccentricity failure because the harmonic content is the same. Moreover, it can only be applied under stationary conditions. In order to overcome these drawbacks, a novel method is used based upon the Hilbert-Huang transform. It represents time-dependent series in a 2-D time-frequency domain by extracting instantaneous frequency components through an empirical-mode decomposition process. This tool is applied by running the motor under nonstationary conditions of velocity. The experimental results show the reliability and feasibility of the methodology in order to diagnose the demagnetization of a PMSM.
38296
Amrhein M.& Krein P.T
Induction Machine Modeling Approach Based on 3-D Magnetic Equivalent Circuit Framework
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 339 – 347
Developments in power electronics technology, materials, and changing application requirements are driving advances in electric machines. Limitations of standard motor design, particularly for induction machines, restrict performance capabilities in drive applications. Current computer-aided design tools are inadequate to overcome these limitations. Lumped-parameter and finite-element models have limited accuracy and heavy computational effort, respectively. Magnetic equivalent circuits (MEC) avoid these limitations. This paper presents an induction machine MEC model geared toward design and based on a 3-D MEC framework introduced in previous work. A matrix formulation suitable for computation is described. Details of mesh generation for the MEC approach are provided. Force and performance estimation are discussed. Simulations based on this approach are able to track dynamic effects, such as rotor slot torque ripple contributions. Comparisons are made to a 500 W purpose-built machine. Results from lumped-parameter and finite-element models and measurements indicate that MECs, corrected for local saturation, are a promising option for design tools.
38297
Cistelecan M.V. et.al
Adjustable Flux Three-Phase AC Machines With Combined Multiple-Step Star–Delta Winding Connections
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 348 – 355
In this paper, a complete theory and analysis method for combined star-delta three-phase windings from the point of view of magnetomotive force spatial harmonics content and equivalent winding factors calculation is developed. The method allows for any spatial angle and any coils percentage distribution between star and delta balanced winding systems. It is proven that connecting the inner delta in the clockwise or counterclockwise direction leads to two different space angles between the star and delta systems and two different steps in the flux level control. It means that, compared to what is known and applied up to now, using n winding sections in each phase, it is possible to obtain 2 n steps (instead of n + 1) in the flux level. To check the analysis validity, two experimental tests are reported on both squirrel-cage, integer-winding, induction motor, and permanent magnet, low-speed, fractional-winding, synchronous generator with a specially designed stator winding, allowing multiple-step air-gap flux regulation.
38298
Wan-Ying Huang & Bettayeb A
Optimization of Magnet Segmentation for Reduction of Eddy-Current Losses in Permanent Magnet Synchronous Machine
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 381 – 387
Rare earth permanent magnet synchronous machines with the pulsewidth modulated supply are exposed to magnets' heating due to harmonic fields, which rotate in relation to rotor. In cases when skin effect is negligible, the corresponding eddy-current losses in magnets can be reduced by segmentation of magnets. In this paper, we propose an analytical method to evaluate the effect of both circumferential and axial segmentations on losses' reduction in various conditions, concerning the skin effect. With the skin effect operating, the magnets' division may lead to increase rather than decrease of the eddy-current losses. A criterion to determine range of parameters leading to this unexpected situation is presented. Finite-element calculation confirms the results of the analysis.
38299
Fukami T.et.al
Steady-State Analysis of a Permanent-Magnet-Assisted Salient-Pole Synchronous Generator
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 388 – 393
This paper presents a simple mathematical model for the steady-state analysis of a permanent-magnet-assisted salient-pole synchronous generator (PMa-SG). The PMa-SG is a new type of salient-pole SG that has PMs between the adjacent pole shoes. The developed model takes into account the magnetic saturation and core loss, and enables quantitative predictions of load characteristics from the no-load test data. The validity of the developed model is confirmed experimentally. The effect of the PMs on the performance characteristics of the PMa-SG is also investigated.
38300
Wrobel R. et.al
Thermal Performance of an Open-Slot Modular-Wound Machine With External Rotor
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 403 – 411
This paper describes the thermal analysis of an external-rotor brushless permanent-magnet motor used in a traction application. The machine has a nonstandard open-slot stator lamination and is wound with a single-layer concentrated ``modular'' winding. This structure potentially has several heat transfer advantages compared to the more traditional double-layer concentrated winding. An analytical lumped-parameter thermal model has been developed for the machine to gain an understanding of the main cooling mechanisms and to investigate the potential heat transfer advantages. The thermal advantage of the modular winding over the more conventional 1.5-slot-per-pole design is presented. Results from the developed thermal model have been validated experimentally on a prototype wheel hub motor.
38301
Yuwen Hu et.al
A Fault-Tolerant Induction Generator System Based on Instantaneous Torque Control (ITC)
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 412-421
A fault-tolerant scheme of an induction generator using instantaneous torque control (ITC) is proposed in this paper. In the case that a power switch of the converter goes wrong, the system can be reconfigured to a four-switch three-phase (FSTP) generator system and continue supplying some power. In the reconfigured system, the ITC strategy can also be applied; the only differences lie in the available voltage space vectors and optimal switching-table. There are only two bridges working in the post-failure operation, which results in halved output power compared with that of prefailure six-switch three-phase system. This paper also investigates the special issues of the voltage ripples and drifts of the midpoint voltage of the dc bus capacitor of the FSTP system. The optimization of capacitor and the improvement of ITC strategy can effectively solve the two issues. In order to further improve the quality of the output dc voltage, the space vector modulation -ITC strategy is examined by modeling and experimental tests, which can greatly reduce the fluctuations of output voltage. Its voltage ripple is only 0.5 V on the output voltage of 270 V dc.
38302
Seok-Hee Han et.al
Reducing Harmonic Eddy-Current Losses in the Stator Teeth of Interior Permanent Magnet Synchronous Machines During Flux Weakening
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 441-449
Interior permanent magnet (IPM) synchronous machines can experience large harmonic eddy-current losses in the stator teeth under flux-weakening operation, significantly depressing the efficiency of these machines at high operating speeds. This paper presents a new analytical/finite-element hybrid design approach to reduce the harmonic eddy-current losses in IPM machine stator teeth during flux-weakening operation. The proposed technique achieves this objective by three steps: 1) developing an analytical index for the harmonic eddy-current losses in IPM machine stator teeth; 2) designing the spatial distribution of the rotor MMF to minimize the analytical index; and 3) synthesizing the rotor geometry to implement the desired rotor MMF function while maintaining the basic machine characteristics unchanged. It will be shown that two-layer rotors, if properly optimized, are significantly more effective than one-layer rotors for the purpose of reducing the harmonic eddy-current losses in IPM machine stator teeth during flux-weakening operation at high speeds.
38303
Kral C.et.al
Phenomenon Rotor Fault—Multiple Electrical Rotor Asymmetries in Induction Machines
IEEE Transactions on Power Electronics, Vol.25; No.5; May 2010; 1124 – 1134
In the literature, the effects caused by a single or several adjacently broken rotor bars, or a broken end ring are thoroughly investigated. The phenomenon of various nonadjacently broken rotor bars has not been studied so far in detail. Since nonadjacently broken rotor bars may give rise to fault signatures, which are not directly related with the fault extent, it is important to understand the nature of multiple electrical rotor asymmetries in induction machines. The purpose of this paper is thus to investigate several combinations of electrical rotor asymmetries, to systematically elaborate the phenomena related to the broken bars and end rings. In this paper, a sophisticated simulation model and measurement results are used to analyze the phenomenon rotor fault.
38304
Jui-Yuan Chai et.al
On the Switched-Reluctance Motor Drive With Three-Phase Single-Switch Switch-Mode Rectifier Front-End
IEEE Transactions on Power Electronics, Vol.25; No.5; May 2010; 1135 – 1148
This paper presents a switched reluctance motor (SRM) drive powered by a three-phase single-switch (3P1SW) switch-mode rectifier (SMR). The digital controls of both power stages are realized in a common DSP. In the front-end SMR, a robust current harmonic cancellation scheme and a robust voltage control scheme are developed. The undesired line current and output voltage ripples are regarded as disturbances and they are reduced via the proposed robust controls. In voltage control, a feedback controller is augmented with a simple robust error canceller. The robust cancellation weighting factor is automatically tuned according to load level to yield compromised voltage and power quality control performances. The chaotic phenomena can be automatically avoided and better SMR operating performance is obtained simultaneously. With boostable and regulated dc-link voltage, the current and speed dynamic responses of the followed SRM drive are enhanced, and the vibration and speed ripple are also lessened. As to the SRM drive, a random-band hysteresis current-controlled pulsewidth modulation (CCPWM) scheme (RB-HCCPWM) with harmonic spectrum shaping is developed and applied for its winding excitation control. The winding current harmonic spectrum is more dispersedly distributed to yield reduced stator vibration and speed ripple. Moreover, the commutation advanced shift is applied to yield further performance improvement of SRM drive.
38305
Suul J.A et.al
STATCOM-Based Indirect Torque Control of Induction Machines During Voltage Recovery After Grid Faults
IEEE Transactions on Power Electronics, Vol.25; No.5; May 2010; 1240 – 1250
This paper proposes a control method for limiting the torque of grid-connected cage induction machines during the recovery process after grid faults, by using a static synchronous compensator (STATCOM) connected at the machine terminals. When a STATCOM is used for transient stability improvement, common practice is to design the control system to keep reactive current at maximum level until the voltage has returned to its initial value. This will result in high torques during the recovery process after grid faults. The control method proposed in this paper is intended to limit such torque transients by temporarily defining a new voltage reference for the STATCOM control system. As torque is controlled through the voltage reference of the STATCOM, the method is labeled indirect torque control (ITC). The presented concept is a model-based approach derived from a quasi-static equivalent circuit of the induction machine, the STATCOM and a Thévenin representation of the power system. For illustration and verification, time-domain simulations of a wind power generation system with a STATCOM at the terminals of an induction generator, are provided. As the objective of limiting the torque of the induction machine is achieved, the derivation of the concept proves to be reasonable. The approach is presented in its most general form, oriented to torque limitation of induction machines both in generating and motoring mode, and is not restricted to the presented example.
38306
Feng Y. N. et.al
Reduced Losses in Die-Cast Machines With Insulated Rotors
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 928 – 936
This paper reports an investigation into the influence of interbar currents on the performance of die-cast cage induction machines. This work is based on an extensive set of experimental measurements using a series of specially made die-cast cage induction motors with bars insulated using alternate processes. Experimental measurements were undertaken separately by the industrial manufacturer and at the university laboratories, and these clearly demonstrate that increasing the insulation of the rotor cage inhibits the flow of interbar current and reduces the total motor losses and increases the motor efficiency as a consequence. The experimental measurements were further validated using an analytical interbar model. Further experimental measurements also demonstrate that insulating the rotor cage also modifies the stator torque in a counterintuitive fashion.
38307
Tuovinen, T et.al
Modeling of Saturation Due to Main and Leakage Flux Interaction in Induction Machines
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 937 – 945
Saturation due to main flux and rotor leakage flux interaction appears in induction machines, particularly if rotor slots are skewed or closed. Conventional saturation models used in connection with dynamic equivalent-circuit models do not take this phenomenon into account. In this paper, explicit functions for modeling this mutual saturation are proposed. These functions are physically reasonable and are easy to fit, and the number of their parameters is small. The proposed functions can be used in real-time applications and in computer simulations if high accuracy and physical consistency are preferable. The model fits well to the data obtained from finite-element analysis or experimental data of a 2.2-kW motor. The model predicts the stator current with good accuracy both in steady state and in transients.
38308
Wolbank T. M. et.al
Autonomous Self-Commissioning Method for Speed-Sensorless-Controlled Induction Machines
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 946 – 954
Speed-sensorless control of ac machines at zero speed is so far only possible using signal injection methods. In particular, when applied to induction machines the spatial saturation leads to a dependence of the resulting control signals on the flux/load level. Usually, this dependence has to be identified on a special test stand during a commissioning procedure for each type of induction machine. In this paper, an autonomous commissioning method based on an artificial neural network approach is proposed that depends on neither a speed sensor present as a reference nor a load dynamometer coupled to the machine and guaranteeing constant speed. The training data for the neural network is obtained using only acceleration and deceleration measurements of the uncoupled machine. The reliability of the proposed autonomous commissioning method is proven by measurement results. When comparing the resulting sensorless control performance, the proposed commissioning method reaches the same level of performance as a manual identification method using a load dynamometer and a speed sensor.
38309
Hinkkanen M
Small-Signal Modeling of Mutual Saturation in Induction Machines
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 965 - 973
A small-signal model is derived for saturated induction machines. Inductances are allowed to saturate as a function of their own current (or flux), and the mutual saturation effect originating mainly from skewed or closed rotor slots is also included in the model. The model fulfills the reciprocity conditions, and it can be applied to parameter identification and to the analysis and development of flux-angle estimation methods. As application examples, the parameters of a 2.2-kW induction machine were identified using the data obtained from time-stepping finite-element analysis and locked-rotor measurements. The proposed model fits well to the data, and the fitted parameters are physically reasonable.
38310
Wu Q.& Nandi S.
Fast Single-Turn Sensitive Stator Interturn Fault Detection of Induction Machines Based on Positive- and Negative-Sequence Third Harmonic Components of Line Currents
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 974 – 983
Unambiguous detection of stator interturn faults for induction machines at their incipient stage, i.e., few turns' fault, has recently received great attention. Traditionally, interturn faults are detected using negative-sequence current and impedance. However, their effectiveness under supply imbalance conditions is questionable. Recently, line-current third harmonic (+3f) has also been used in an attempt to achieve this goal. Nevertheless, issues such as inherent structural asymmetry and voltage imbalance also influence the +3f. In this paper, the positive- and negative-sequence third harmonics (±3f) of line current under different operating conditions have been explored by combining space and time harmonics. The suggested fault signature was obtained by removing residual components from tested quantities. Simulation and experimental results using 1 s of data indicate that the proposed (±3f) signatures are capable of very effectively detecting even a single-turn fault, and distinguish it from voltage imbalance and structural asymmetry.
38311
Marignetti F.
On Liquid-Nitrogen-Cooled Copper-Wound Machines With Soft Magnetic Composite Core
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 984 - 992
This paper illustrates the potential and the convenience of copper-wound electrical machines with liquid nitrogen (LN) cooling. Natural convection heat exchange coefficients in LN are very high. Moreover, the resistivity of copper decreases remarkably at cryogenic temperature, subsequently reducing Joule loss in copper windings. Hence, cryogenic copper-wound electrical machines use less copper to carry the same current compared to air- or water-cooled machines, thereby improving the power-to-weight ratio. An experimental study is made of some practical issues related to the design of an LN-cooled machine using as an example the construction of a 220-N permanent magnet tubular linear actuator with a soft magnetic composite stator core.
38312
Padron J.F.M et.al
Calculating Steady-State Operating Conditions for Doubly-Fed Induction Generator Wind Turbines
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 922-928
In this paper an analysis of steady-state operation in doubly-fed induction generator (DFIG) wind turbines (WT) is presented. A method based on the Newton-Raphson (NR) algorithm is proposed for obtaining the steady-state electrical variables of the machine under certain given conditions. It is of interest in the load flow analysis, when these machines are present in electrical system, but also for gaining initial conditions for dynamic analysis, as the variables in dynamic models must coincide with those in stationary models during steady-state operation. Results obtained from the stationary analysis allow us to initialize electrical variables for use in a third-order dynamic model of the DFIG. The method presented in this paper does not make use of a d-q reference frame. Some approximations made in other works have not been assumed here, which allowed us to obtain more accurate results.
38313
Liwei Wang & Jatskevich J.
Including Magnetic Saturation in Voltage-Behind-Reactance Induction Machine Model for EMTP-Type Solution
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 975 – 987
A voltage-behind-reactance (VBR) machine model has been recently proposed for the electro-magnetic transient programs (EMTP)-type simulation programs. The VBR model greatly improves numerical accuracy and efficiency compared with the traditional qd and phase-domain (PD) models. This paper extends the previous research and presents an approach to include magnetic saturation into the VBR induction machine model. The presented method takes into account the qd axes static and dynamic cross saturation, whereas the nonlinear magnetic characteristic is represented using a piecewise-linear method that is suitable for the EMTP solution approach. Case studies verify the new saturable VBR model and show that it has improved numerical stability and accuracy even at large time steps.
38314
Liwei Wang & Jatskevich J.
Approximate Voltage-Behind-Reactance Induction Machine Model for Efficient Interface With EMTP Network Solution
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 1016 – 1031
A so-called voltage-behind-reactance (VBR) induction machine model has recently been proposed for the Electro-Magnetic Transient Program (EMTP) solution as an advantageous alternative to the traditional qd and phase-domain (PD) models. This paper focuses on achieving an efficient interface of the machine models with the EMTP network. It is shown first that a discretized PD model can be formulated to have a constant machine conductance submatrix, which is a very desirable numerical property that allows avoiding the re-factorization of the network conductance matrix at every time step. Furthermore, an approximate voltage-behind-reactance (AVBR) model is proposed where the rotor-speed-dependent coefficients are neglected, thus leading to a similar constant machine conductance submatrix and efficient interface. Case studies demonstrate that the new AVBR model represents a significant improvement in terms of numerical accuracy and efficiency over other established models used in EMTP.
1.2 ELECTRICAL MOTORS & DRIVES
38315
Sonnaillon, M.O.et.al
Online Sensorless Induction Motor Temperature Monitoring
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 273 – 280
A sensorless internal temperature monitoring method for induction motors is proposed in this paper. This method can be embedded in standard motor drives, and is based on the stator windings resistance variation with temperature. A small AC signal is injected to the motor, superimposed to the power supply current, in order to measure the stator resistance online. The proposed method has the advantage of requiring a very low-level monitoring signal, hence the motor torque perturbations and additional power losses are negligible. Furthermore, temperature estimations do not depend on the knowledge of any other motor parameter, since the method is not based on a model. This makes the proposed method more robust than model-based methods. Experimental results that validate the proposal are also presented.
38316
Nakahama T et.al
Effects of Fan Blade Forward-Swept and Inclined Amounts in Electric Motors
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 457 – 464
This paper studies the effects of blades' forward-swept amount in the rotation direction and forward-inclined amount in the intake direction on the flow around the fan blades of a large open-type motor. The authors have previously clarified this flow separation on the blade surface under high ventilation resistance from flow analysis and visualization experiments. To prevent flow separation, they proposed forward-swept and inclined blades, together with reduction of the air path's ventilation resistance. In this study, numerical fluid analyses were performed on the flow around forward-swept and inclined blades of axial fans for large open-type motors. Several combinations of forward-swept and inclined amounts were studied. The relationship between forward-swept and inclined amounts and flow was evaluated quantitatively, and an ideal combination was obtained. The study revealed that an axial fan with this combination showed much higher flow rate than a conventional fan without forward-swept and inclined blades. Furthermore, it significantly decreased fluid noise and axis power.
38317
Idjdarene K. et.al
Performance of an Isolated Induction Generator Under Unbalanced Loads
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 303 – 311
In this paper, the performance of an isolated self-excited induction generator driven by a wind turbine under unbalanced loads is studied. First, the whole system, including the induction generator, the capacitors, and the loads, is modeled. The model used for the isolated induction generator is a diphase one obtained, using the Park transformation. This model allows the saturation effect to be taken into account, assuming certain simplifying hypotheses. Then, the developed model is validated comparing simulation and experiment results at no load and for balanced load cases. Finally, the same model is used to study the performance of the isolated induction generator under unbalanced load cases. Compared to the experiments, the simulation results show a good prediction of the electrical variable waveforms. Furthermore, it can be seen that the magnitude and frequency of the voltages do not vary a lot even if the load is hardly unbalanced.
38318
Linni Jian & Chau K.T.
A Coaxial Magnetic Gear With Halbach Permanent Magnet Arrays
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 319 – 328
This paper proposes a coaxial magnetic gear that offers higher torque density, lower cogging torque, and lower iron losses than its counterparts. The key is to newly employ a Halbach permanent-magnet (PM) array to constitute the PM poles in the inner rotor and a partial Halbach array (two segments per pole) for the outer rotor. The corresponding magnetic field distributions, torque transmission, and torque ripples are analytically discussed. Then, the corresponding performances are quantitatively assessed by using the finite-element method.
38319
Si Zhe Chen et.al
Integral Sliding-Mode Direct Torque Control of Doubly-Fed Induction Generators Under Unbalanced Grid Voltage
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 356 – 368
An integral sliding-mode direct torque control (ISM-DTC) scheme with space-vector modulation for wind-energy conversion systems based on doubly-fed induction generators (DFIGs) under unbalanced grid voltage is proposed. The torque and power pulsations at twice the grid frequency caused by unbalanced grid voltage can be minimized by the proposed ISM-DTC scheme. Compared with existing control schemes of DFIGs under unbalanced grid voltage, the parametric uncertainties are included into the design procedure of sliding-mode controller, which guarantees the robustness of the controller. Because the torque and reactive power are directly controlled by the rotor voltage, the measurement, coordinate transformation, and symmetrical component extraction of rotor current are eliminated, which simplifies the structure of the controller. Simulation and hardware implementation results validate the effect and parametric robustness of the proposed ISM-DTC scheme
38320
Singh B. et.al
Harmonics Mitigation in LCI-Fed Synchronous Motor Drives
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 369 – 380
A load-commutated inverter (LCI) fed synchronous motor (SM) is operated as an adjustable speed drive (ASD) in high-power applications. These drives are known as commutatorless motor (CLM) drives and posses many promising features like high efficiency, economic operation, and flexibility of control in high-power ratings. The CLM drives are used in compressors, blowers, fans, pumps, and mill drives for a range of industries as mining, water treatment plants, chemical, paper, textile, cement, rolling mills, and petrochemical plants. However, the power quality (PQ) problems at ac mains have been the concerns in these drives as the LCI has front-end thyristor converter injecting harmonics in the supply. This paper investigates various topologies for the mitigation of PQ problems in LCI-fed SM drives using multipulse ac-dc converters. A set of hybrid topologies is proposed, which use a combination of a passive filter with a multipulse converter to feed CLM. A basis for selection of a suitable ac-dc converter is presented for PQ improvement at the input mains of the LCI-fed SM drives.
38321
Jin Yang et.al
A Series-Dynamic-Resistor-Based Converter Protection Scheme for Doubly-Fed Induction Generator During Various Fault Conditions
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 422 – 432
This paper proposes a new converter protection method, primarily based on a series dynamic resistor (SDR) that avoids the doubly-fed induction generator (DFIG) control being disabled by crowbar protection during fault conditions. A combined converter protection scheme based on the proposed SDR and conventional crowbar is analyzed and discussed. The main protection advantages are due to the series topology when compared with crowbar and dc-chopper protection. Various fault overcurrent conditions (both symmetrical and asymmetrical) are analyzed and used to design the protection in detail, including the switching strategy and coordination with crowbar, and resistance value calculations. PSCAD/EMTDC simulation results show that the proposed method is advantageous for fault overcurrent protection, especially for asymmetrical faults, in which the traditional crowbar protection may malfunction.
38322
Gadoue S.M.et.al
MRAS Sensorless Vector Control of an Induction Motor Using New Sliding-Mode and Fuzzy-Logic Adaptation Mechanisms
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 394 – 402
In this paper, two novel adaptation schemes are proposed to replace the classical PI controller used in model reference adaptive speed-estimation schemes that are based on rotor flux. The first proposed adaptation scheme is based on sliding-mode theory. A new speed-estimation adaptation law is derived using Lyapunov theory to ensure estimation stability, as well as fast error dynamics. The other adaptation mechanism is based on fuzzy-logic strategy. A detailed experimental comparison between the new and conventional schemes is carried out in both open- and closed-loop sensorless modes of operation when a vector control drive is working at very low speed. Superior performance has been obtained using the new sliding-mode and fuzzy-logic adaptation mechanisms in both modes of operations.
38323
Xiuhe Wang et.al
Study of a Novel Energy Efficient Single-Phase Induction Motor With Three Series-Connected Windings and Two Capacitors
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 433 – 440
This paper presents a novel energy efficient single-phase induction motor with three series-connected windings and two capacitors. By suitable selection of capacitors, the currents in three windings are approximately symmetrical, and thus, the motor can operate approximately symmetrically from single-phase supply. Based on the symmetrical components method, the condition for balanced operation is studied, and the method for determining capacitances is proposed. The performance analysis method is put forward to calculate the steady performances. Performance tests are performed on the proposed motor and three-phase induction motor. It is proved that their rated efficiency is approximately the same, while the power factor of the former is higher than that of the latter. In comparison with the ordinary single-phase induction motor, it has the advantages of higher efficiency and smaller volume, thus can take the place of the latter in some applications.
38324
Kolehmainen J.
Synchronous Reluctance Motor With Form Blocked Rotor
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 450 – 456
A novel type of mechanically robust synchronous reluctance rotor structure is proposed for medium speed synchronous reluctance machines. A machine utilizing the construction is built, tested, and compared to another machine with the common synchronous reluctance rotor structure. The machine is also simulated using the finite element method and the results are compared to the tested values. The obtained results demonstrate the feasibility of the construction.
38325
Maillet Y. et.al
High-Density EMI Filter Design for DC-Fed Motor Drives
IEEE Transactions on Power Electronics, Vol.25; No.5; May 2010; 1163 – 1172
This paper presents strategies to reduce both differential-mode (DM) and common-mode (CM) noise using a passive filter in a dc-fed motor drive. The paper concentrates on the type of grounding and the components to optimize filter size and performance. Grounding schemes, material comparison between ferrite and nanocrystalline cores, and a new integrated filter structure are presented. The integrated structure maximizes the core window area and increases the leakage inductance by integrating both CM and DM inductances onto one core. Small-signal and large-signal experiments validate the structure, showing it to have reduced filter size and good filtering performance when compared with standard filters at both low and high frequencies.
38326
Hinkkanen M et.al
Reduced-Order Flux Observers With Stator-Resistance Adaptation for Speed-Sensorless Induction Motor Drives
IEEE Transactions on Power Electronics, Vol.25; No.5; May 2010; 1173 – 1183
This paper deals with reduced-order flux observers with stator-resistance adaptation for speed-sensorless induction motor (IM) drives. A general analytical solution for the stabilizing observer gain is given. The gain has two free positive parameters (which depend on the operating point), whose selection significantly affects the damping, convergence rate, robustness, and other properties of the observer. The general stability conditions for the stator-resistance adaptation are derived. An observer design is proposed that yields a robust and well-damped system and requires a minimal amount of tuning work. The proposed observer design is experimentally tested using a 45-kW IM drive; stable operation at very low speeds under different loading conditions is demonstrated.
38327
Jacobina, C.B.
Single-Phase to Three-Phase Drive System Using Two Parallel Single-Phase Rectifiers
IEEE Transactions on Power Electronics, Vol.25; No.5; May 2010; 1285 – 1295
This paper proposes a single-phase to three-phase drive system composed of two parallel single-phase rectifiers, a three-phase inverter, and an induction motor. The proposed topology permits to reduce the rectifier switch currents, the harmonic distortion at the input converter side, and presents improvements on the fault tolerance characteristics. Even with the increase in the number of switches, the total energy loss of the proposed system may be lower than that of a conventional one. The model of the system is derived, and it is shown that the reduction of circulating current is an important objective in the system design. A suitable control strategy, including the pulsewidth modulation technique (PWM), is developed. Experimental results are presented as well.
38328
Makaran J.E
Gate Charge Control for MOSFET Turn-Off in PWM Motor Drives Through Empirical Means
IEEE Transactions on Power Electronics, Vol.25; No.5; May 2010; 1339 – 1350
The following paper presents a novel, empirical approach to gate charge control of a MOSFET used in low-side drive applications such as found in dc motor drives during turn-off, using pulsewidth modulation (PWM) based on ideal expressions of MOSFET behavior during turn- off. Without gate charge control, ringing and overshoot caused by dv /dt effects during the turn-off can result in an increase in electromagnetic interference as well as an increased power dissipation. The ringing can be difficult to suppress through the addition of suppression components as they add cost and bulk to the motor controller. Previous work has focused on the observation of dv/ dt, feed-forward, or open-loop means. Although complex gate charge solutions exist in dedicated application-specific integrated circuits (ASICs), a simple, cost-effective solution is proposed in this paper. This solution differs from previous solutions, making use of the ideal relationship between the drain-to-source and gate-to-source voltage of the MOSFET on turn-off to determine the region of high dv/dt to control a two-staged gate charge removal scheme. This solution can be readily implemented in microprocessor-based control schemes used to control motor drives and switch-mode power supplies utilizing low-side MOSFET switching. Circuit operation and advantages are presented and supported by simulation and experimental results.
38329
Koran A et.al
Design of a Photovoltaic Simulator With a Novel Reference Signal Generator and Two-Stage LC Output Filter
IEEE Transactions on Power Electronics, Vol.25; No.5; May 2010; 1331 – 1338
This paper presents a systematic design technique for a photovoltaic (PV) simulator. The proposed technique helps to improve control loop bandwidth and system response. The PV equivalent circuit is used to generate the current-voltage reference curves. A novel technique is proposed and implemented with analog controllers to simplify the reference signal generator, and to avoid computation time delays in digital controllers. A two-stage LC output filter is implemented to push the resonant frequency higher, and thus, allowing a higher bandwidth control loop design while keeping the same switching ripple attenuation as in the conventional one-stage LC output filter. Design procedures for both control and power stage circuits are explained. Experimental results verify the steady state and transient performance of the proposed PV simulator at 2.7 kW output.
38330
Hwu K.I. & Yau Y.T.
Performance Enhancement of Boost Converter Based on PID Controller Plus Linear-to-Nonlinear Translator
IEEE Transactions on Power Electronics, Vol.25; No.5; May 2010; 1351 – 1361
Here, A PID controller plus a novel linear-to-nonlinear translator is proposed and applied to the boost converter to improve the operating performance of the boost converter under large transient variations in load all over the quiescent dc input voltage range. The proposed translator is inserted between the PID controller and the main power stage such that the PID controller considers the behavior of the boost converter to be quasi-linear, thereby suppressing the effect of nonlinear behavior of the boost converter on the PID controller. Besides, variations in dc gain of the control-to-output transfer function with the translator are smaller than those without the translator, thus making system control easy to attain. Also, one-comparator counter-based sampling without any A-D converter is presented herein to realize the proposed control strategy. As mentioned above, the proposed control strategy can make the boost converter stably operated under large load transient responses all over the quiescent dc input voltage range.
38331
Das A. & Gopakumar K.
A Voltage Space Vector Diagram Formed by Six Concentric Dodecagons for Induction Motor Drives
IEEE Transactions on Power Electronics, Vol.25; No.6; June 2010; 1480 – 1487
A new voltage space vector diagram consisting of six concentric dodecagons is proposed in this paper. The space vector diagram is developed for an open-end induction motor drive fed from two three-level neutral point clamped (NPC) inverters with asymmetric isolated dc voltage sources. As already reported in literature, a dodecagonal space vector diagram is advantageous over a hexagonal one, since the 6n± 1 (n = odd) harmonics are absent in the phase voltage and the linear modulation range is extended. The present work further improves the existing dodecagonal space vector diagrams by dividing the space vector plane into six concentric dodecagons, while retaining the aforementioned advantages. A high-resolution pulsewidth modulation strategy is developed in this paper, which compared to existing schemes, reduces the harmonic content of the motor phase voltage without resorting to higher switching frequency. A comparative study of output voltage quality produced by the proposed topology and a five-level inverter shows substantial improvement in the present work. At the same time, the present topology does not require any special design of the inverter and uses two popular three-level NPC inverters. Experimental verification on a laboratory prototype indicates the possible application of this concept for high power drives.
38332
Shami U. T.& Akagi H.
Identification and Discussion of the Origin of a Shaft End-to-End Voltage in an Inverter-Driven Motor
IEEE Transactions on Power Electronics, Vol.25; No.6; June 2010; 1615 – 1625
This paper addresses shaft end-to-end and shaft-to-frame voltages that appear in the 400-V 15-kW induction motor driven by a voltage-source pulsewidth modulation inverter. It has been known that an inverter-fed common-mode voltage causes both shaft voltages. Extensive experiments are performed with an ungrounded motor subjected to a differential-mode voltage. Experimental results show that the differential-mode voltage applied across three-phase, two-phase, or single-phase stator windings also causes a shaft end-to-end voltage. It is concluded that the combination of a steep change in differential-mode voltage and high-frequency motor asymmetry causes a shaft end-to-end voltage. A motor model is presented to explain the generation of shaft end-to- end voltage.
38333
Ishibashi F. et.al
Change of Mechanical Natural Frequencies of Induction Motor
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 922 - 927
Most electromagnetic acoustic noise of induction motors is generated when the mechanical natural frequencies of the stator coincide with or are close to the frequencies of magnetomotive forces. In order to avoid this, it is necessary to determine the motor's mechanical natural frequencies by calculation or simulation. Variation of natural frequency from yoke steel ring to motor has been studied experimentally, analytically and by structural finite-element method analysis. It thus became clear that mechanical natural frequencies increased in number and natural frequencies gradually decreased from simple yoke steel ring to motor.
38334
Kano Y.
Optimum Design Approach for a Two-Phase Switched Reluctance Compressor Drive
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 955 – 964
This paper presents an optimum design approach to a two-phase switched reluctance motor (SRM) drive. The proposed drive is designed for use as a compressor drive in a small refrigerator as an alternative to the existing brushless dc motor with rare-earth magnets. In the proposed approach, three genetic algorithm loops work to optimize the lamination design and to meet the requirements for the target application while simultaneously fine-tuning the control parameters. To achieve design optimization within a realistic timescale, the repeated calculation required to obtain fitness evaluation does not use finite-element analysis but instead consists of a dynamic simulator based on an analytical expression of magnetizing curves and a geometric flux-tube-based nonlinear magnetic analysis developed specifically for this class of motor. Design results show that the proposed approach can autonomously find a feasible design solution of an SRM drive for the target application from a huge search space. The experimental studies using a two-phase 8/6 prototype manufactured in accordance with the optimized design parameters show the validity of the proposed design approach.
38335
Alberti L et.al
IPM Machine Drive Design and Tests for an Integrated Starter–Alternator Application
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 993 – 1001
This paper deals with an integrated starter–alternator (ISA) drive which exhibits a high torque for the engine start, a wide constant-power speed range for the engine speedup, and a high-speed generator mode operation for electric energy generation. Peculiarities of this ISA drive are thus its flux-weakening capability and the possibility to large torque overload at low speed. The focus on the design, analysis, and test of an interior permanent-magnet motor and drive for a prototype of ISA is given in this paper. In details, this paper reports on the design of stator and rotor geometries, the results of finite-element computations, the description of control system, and the experimental results of prototype tests.
38336
Nied N. et.al
Soft Starting of Induction Motor With Torque Control
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 1002 – 1010
This paper presents a simple technique based on stator-flux estimation to control the electromagnetic torque of induction motors (IMs) during soft starting. The inherent problems related to pure integration of the back electromagnetic force to estimate the stator flux are minimized using the low-pass-filter approach. The experimental results are dealt with and compared with the usual current-control technique. The results obtained validate the proposed technique, showing its viability in applications where the objective is to fit the IM torque profile during starting or stopping according to the load torque.
38337
Holtz J. & Oikonomou N.
Optimal Control of a Dual Three-Level Inverter System for Medium-Voltage Drives
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 1034 – 1041
Actual developments in medium-voltage drives aim at increasing the power capability of pulsewidth modulated (PWM) inverters. Parallel connection of power semiconductor devices permits increasing the output current, whereas series-connected devices increase the output voltage. In either case are additional means required for balancing the current or voltage stress of the devices. The three-level neutral-point-clamped inverter topology offers an inherent means to ensure dynamic voltage balancing of a maximum of two series-connected devices. Higher operating voltages can be achieved by series connection of entire inverter topologies. Two circuit topologies that behave as five-level units are considered. Synchronous optimal PWM is applied for their control. This permits reducing the switching frequency to the 100-Hz region without sacrificing on harmonic distortion.
38338
Khan M. A. S. K. & Rahman M. A.
A Novel Neuro-Wavelet-Based Self-Tuned Wavelet Controller for IPM Motor Drives
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 1194 – 1203
This paper presents a hybrid neuro-wavelet scheme for online tuning of a wavelet-based multiresolution proportional integral derivative (MRPID) controller in real time for precise speed control of an interior permanent-magnet synchronous motor (IPMSM) drive system under system uncertainties. In the proposed wavelet-based MRPID controller, the discrete wavelet transform (DWT) is used to decompose the speed error between actual and command speeds into different frequency components at various scales of the DWT. The MRPID controller parameters are tuned online by the wavelet neural network (WNN) to ensure optimal performance of the drive system. The neuro-wavelet-based MRPID controller is trained online with adaptive learning rates in the closed-loop control of the IPMSM drive system. The adaptive learning rates are derived using the discrete Lyapunov stability theorem so that the convergence of speed tracking error could be guaranteed in the closed-loop system. The performance of the proposed hybrid controller is investigated in both simulation and experiments at different dynamic operating conditions. The complete vector control scheme incorporating the proposed self-tuning MRPID controller is successfully implemented in real time using the digital signal processor board ds1102 for the laboratory 1-hp interior permanent-magnet motor. The superior performance of the proposed WNN-based self-tuning MRPID controller is also validated over fixed-gain controllers.
38339
Uddin M. N. & Chy M. M. I.
A Novel Fuzzy-Logic-Controller-Based Torque and Flux Controls of IPM Synchronous Motor
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 1220 – 1229
This paper presents a novel fuzzy logic controller (FLC)-based wide-speed-range operation of interior permanent-magnet synchronous motor (IPMSM) drives. The proposed FLC is designed in such a way that it can simultaneously control both torque and flux of the motor while maintaining current and voltage constraints. Thus, a stand-alone FLC is utilized, whose outputs are d- and q -axis currents. The proposed FLC is designed based on conventional maximum torque per ampere operation below the rated speed and the field-weakening operation above the rated speed. The complete IPMSM drive is experimentally implemented, utilizing dSPACE DSP board DS1104 for a prototype 5-hp motor. The performance of the proposed drive is tested both in simulation and experiment at different operating conditions. The robustness of the controller and its prospective real-time industrial drive application are evidenced by the results.
38340
Dragan C. et.al
Tribocharging of Insulating Powders in the Annular Ducts of Pneumatic Devices
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 1138 – 1143
The aim of the experiments reported in this paper was to evaluate the tribocharging phenomena that might occur in the annular ducts specific to the cyclonelike aspiration unit of a suction-type dilute-phase pneumatic transport system. The experiments were carried out with two types of powders, on two models of ducts, having the same geometrical characteristics but being built of different materials. It was found that the charge acquired by the particles strongly depends on the nature of the material of the annular ducts. This triboelectric effect might be effectively employed for the selective charging and electrostatic separation of granular or pulverulent mixtures of insulating materials.
2. INSULATION SYSTEM, MATERIALS & INSULATORS
38341
Fernando M.A.R.M & Gubanski S.M.
Ageing of silicone rubber insulators in coastal and inland tropical environment
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 326 - 333
This paper presents investigations on the performance of 33 kV silicone rubber insulators characterized by different creepage lengths, which aimed to find out whether the insulators could permanently work when electrically stressed beyond the recommended limits in polluted and clean tropical environments. The study was performed under natural field and laboratory conditions. The insulators tested included eight types of silicone rubber composite insulators, one type of hybrid silicone-ceramic insulator and one semi-conducting glazed porcelain insulator, while ordinary porcelain and glass insulators were used as reference. During the field investigation, two sets of the insulators were separately installed and energized in coastal and inland parts of Sri Lanka, being by that exposed to marine and clean tropical environments. Their performances were periodically evaluated by visual inspections and measurements of hydrophobicity class. After five years of field exposure, the insulator performances were evaluated in laboratory by measurements of leakage currents under clean fog conditions and of wet flashover voltage. A third set of the insulators was aged in laboratory for 1000 hours inside a salt fog chamber where the insulators were continuously energized and daily sprayed with salt solution for eight hours and left to rest for remaining 16 hours. This treatment represented conditions similar as those in the field i.e. insulators exposed to salt sprays during monsoons. The insulator performances were investigated by measurements of leakage currents and classifying their patterns into different categories, i.e. capacitive, resistive, non-linear, discharge and strong discharge types, by means of fast Fourier transform and short time Fourier transform analyses. It was found that the long-term field exposure yielded weaker insulator deterioration than the salt fog chamber ageing, which indicated for a possibility to increase the electric stress on silicone rubber insulat- - ors to levels higher than the ones used today on glass and porcelain counterparts.
38342
Iyer G. et.al
Prediction of electrical performance of medium voltage epoxy insulated equipment
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 334 – 342
The paper presents a theoretical model based on the 2-parameter Weibull Distribution to predict the performance of cycloaliphatic based medium voltage (< 100 kV) insulation equipment. The model combines two prominent modes of degradation, namely surface damage (tracking and erosion) and flashover. New samples and samples that were aged in service and in outdoor test sites were evaluated. The flashover model is based on evaluating surface resistance under wet conditions. The degradation model is based on evaluating the tracking and erosion resistance in the Inclined Plane (ASTM D2303) test. The predictions of the model are shown to be in good agreement with experimental results. A total of 20 insulators and instrument transformers (new and field-aged) were evaluated.
38343
Haddad A et.al
A new approach to anti-fog design for polymeric insulators
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 343 – 350
Electric field strength and leakage current density in the shank region of a polluted polymeric insulator may cause local dry-banding, with a risk of long-term degradation from partial-arc discharges. In a novel approach to dry-band control, the characteristics of silicone rubber surfaces with a textured finish are investigated and, depending on the geometry chosen for the texture, two useful objectives can be achieved. First, the increase of surface area can both reduce the leakage current density in the vulnerable shank region, and also increase the longitudinal creepage distance. Secondly, the damage arising from surface discharges can be mitigated. The principles of the proposed anti-fog design are described in detail. While complete prototype insulators are now being specified for fabrication, this paper reports preliminary results from tests using rectangular samples, which show an improvement in performance. The tests are of two kinds: a) inclined-plane, to assess erosion and tracking on rectangular samples of insulation materials. Such samples have been prepared both with a conventional plane surface and with a textured surface for comparative tests; b) clean-fog tests that use an initially dry pollution layer of known salinity. Here, plane and textured samples have been used for comparative tests, where leakage current and discharge activity are monitored during the generation of the fog.
38344
Xingliang Jiang
Effect of hydrophobicity coating on insulator icing and DC flashover performance of iced insulators
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 351 – 359
How to decrease the ice on insulators and increase the flashover voltage of iced insulator are hot topics of power system in the world. Many tests have been carried out to investigate whether the permanent room temperature vulcanized (PRTV) coating can change the electrical characteristics of iced insulators both in laboratory and field. Firstly, the test to investigate the icing and electrical characteristic of dc insulator with PRTV coating was carried out. Moreover, comparison has been made between artificial polluted insulator and field polluted insulators. Results indicate that the PRTV coating can not decrease the ice accretion on insulators. Instead, it results in accumulating more ice at the beginning of icing regime, but the influence of PRTV coating will not be remarkable to accumulate ice when there is heavy ice on insulators. . In addition, the PRTV coating can decrease the flashover voltage by 10%. It is also revealed that the flashover voltage for the artificial polluted insulators is lower than that of the field polluted insulators due to the non-uniform of the natural pollution.
38345
Wankowicz J. & Bielecki J.
Models of the long-term mechanical strength of long rod composite insulators
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 360 – 367
Different mathematical models of long-term fatigue strength of long-rod insulators were evaluated by studying the effects of superimposed cyclic and constant loads. It has been shown that the strength of composite insulators can well be represented by the power type behavior of the fatigue characteristics and that the time to fatigue failure of a composite insulator strongly depends of the cyclic load amplitude and the maximum level of the total load. It has also been shown that the diameter of the core of composite insulator with crimp-mounted end fittings is the major factor determining the insulator's fatigue and static strength.
38346
Xidong Liang et.al
Surface micro-crack initiated brittle fracture in fiber reinforced plastic rod of composite insulator
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 368 – 374
Previous studies on brittle fracture of composite insulator were concluded, and unanswered questions were analyzed. Almost all the previous studies focus on the source of corrosion medium (the acid) and the mechanical load in brittle fracture, but the stress concentration of stress corrosion fracture was neglected. Sand paper polishing in the manufacturing process of composite insulator may lead to surface micro-cracks with the depth deeper than 30 mm – 40 mm on the fiber reinforced plastic (FRP) rod surface. Stress concentration caused by surface micro-crack in FRP rod and its influence on brittle fracture was noticed in experimental study. The importance of the surface micro-crack in FRP rod was verified by a series of experimental studies. An explanation of the randomness of brittle fracture in composite insulator was put forward. Finally, the actions that should be taken to prevent brittle fracture of composite insulator were emphasized.
38347
Rowland S et.al
Electrical and material characterization of field-aged 400 kV silicone rubber composite insulators
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 375 – 383
This paper presents the electrical and material characteristics of field-aged silicone rubber composite insulators, which have been deployed for 15 years on a 400 kV transmission line in a coastal region of the UK. There were no indications of reduced performance in service. Observations indicate non-uniform aging of the insulators on the different surfaces of the insulator sheds and core, along the insulator string length and in the different compass orientations. A uniquely large number of contact angle measurements, made on each of the insulators' different surfaces, confirm the visual aspect of nonuniform aging. Electrical investigations of the insulators have been performed in terms of leakage current analysis, ac flashover / withstand and switching-surge impulse flashover. A correlation is seen between the ac leakage current and the hydrophobicity measurements. Energy dispersive X-ray (EDX) and Fourier transform infrared spectroscopy (FTIR) analysis of the changes of the materials' surface chemistry is presented. The role of solar radiation and organic growth appears critical to the observed non-uniform aging and must be considered if the longer term operation of the insulator is to be forecast. It is proposed that a reduction of the difference between positive and negative wet-flashover voltages may be a good indicator of early insulator aging.
38348
Gutman I & Dernfalk A.
Pollution tests for polymeric insulators made of hydrophobicity transfer materials
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 384 – 393
There are no standardized methods available at present for artificial pollution testing of polymeric insulators. Modified Salt Fog and Solid Layer tests based on procedures described in IEC 60507, intended for ceramic insulators, are thus often applied. Among methods evaluated for polymeric insulators made of hydrophobicity transfer materials (HTM), a modified Solid Layer test with preconditioning by dry powder is considered as being representative and most promising for future standardization. Further, the proposed procedure allows for testing at different hydrophobic states of the polluted insulators via the introduction of defined time between the application of pollution and voltage test. Finally, if the 50% flashover voltage is determined using e.g. the up-and-down method, results of the tests can be directly applied for insulator selection and dimensioning by means of statistical or deterministic methods.
38349
Schmuck F. et.al
A proposal for intensified inspection and acceptance tests of composite insulators as an addition to the guidelines of IEC 61109 Ed. 2: 2008 and IEC 61952 Ed. 2: 2008
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 394 – 401
The paper provides an example of a test programme, which aims to add to the evaluation of composite insulators after they have being supplied. It is to be considered as a tool to prove the product quality versus the submitted reports from international standards. The proposed tests are not selected to discriminate against any particular material or nufacturer but rather to consider well accepted and recently developed test philosophies, in order to safeguard the quality of the supplied insulators, in particular for bulk volume contracts.
38350
Qaddoumi N.et.al
Detecting defects in outdoor non-ceramic insulators using near-field microwave non-destructive testing
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 402 – 407
This paper presents a novel near-field microwave nondestructive testing technique for defect detection in non-ceramic insulators (NCI). In this work, distribution class 33 kV NCI samples with no defects, air voids in silicone rubber, cracks in the fiberglass core and small metallic inclusion between the fiber core and shank were inspected. The microwave inspection system utilizes an open-ended rectangular waveguide sensor operating in the near-field at a frequency of 24 GHz. The used inspection system is simple, safe and relatively inexpensive. A data acquisition system was used to record the measured data. The results showed that all defects were repeatedly detected with high sensitivity. Line scans of the samples were obtained revealing the presence of different defects and their location. The technique also demonstrated ability to detect thickness variations in the silicon rubber shank.
38351
Platek R et.al
Fluid influence on dynamic characteristics of transformer-bushing system using fluid structure interaction (FSI) approach
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 408 – 416
Currently used procedures for seismic qualifications of HV bushings are based on the analytical equations, and very often are verified by shake table tests. As many specialists claim this approach does not fully reflect the real behavior of the bushing coupled with the transformer tank during seismic loads. In the paper a new methodology for seismic analysis of the transformer/bushing system has been presented using complex numerical simulations. In the proposed approach Fluid Structure Interaction is involved. The methodology has been experimentally verified and can provide useful information for proper design of transformer tank and bushings with high resistance to seismic loads.
38352
Waters R.T et.al
Partial-arc and spark models of the flashover of lightly polluted insulators
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 417 - 424
The established model of the flashover of an insulator, whose surface is covered with a moist, conducting layer of pollution, envisages that it develops from the formation and bridging of a dry band by a partial-arc pre-discharge. This pre-discharge is assumed to possess arc characteristics, so that the electric field across the dry band will fall as the partial arc current increases. Observations of insulators which are only lightly polluted, however, show that pre-discharges are of low luminosity and rich in ultraviolet, and resemble the spark leader inception and extension sequence in air gaps. This is because the current limitation by low values of surface-layer conductance can inhibit the transition to an arc at the pre-discharge stage. An alternative model using simplified voltage-current equations is developed to represent these spark properties rather than an arc characteristic. The predictions of the partial-arc model and this new approach are both tested here, using published experimental data from light-pollution fog tests in the authors' laboratory. For this purpose, the partial-arc theory is further developed in order to reveal its implied prediction for the increase of pre-discharge length with applied voltage before flashover. A corresponding relationship is obtained for the increase of spark leader length using the new model. It is found that for light pollution, the dry-band spark model better represents the test data than the partial-arc model. Consequent predictions are made for the variation of flashover voltage with pollution severity in this regime, which may account for anomalous insulation failures.
38353
Zhijin Zhang et.al
Influence of low atmospheric pressure on AC pollution flashover performance of various types of insulators
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 425-433
The electrical performance of outdoor insulators decreases under low air pressure conditions. The ac pollution flashover performance of various types of insulators are investigated in the multifunction artificial climate chamber in the State Key Laboratory of Power Transmission Equipment and System Security and New Technology, Chongqing University. The field investigation of the ac pollution flashover voltage performance are carried out at three different high altitudes including Wangkun station (altitude of 4484 m), Nachitai station (altitude of 3575 m) along the Qingzang railway and Geermu urban (altitude of 2820 m). The test results indicate that the characteristic exponent n describing the influence degree of air pressure on pollution flashover voltage, which has influence on the pollution flashover voltage of insulators, is variable, and the value of n is related to the pollution, insulator type etc. Under ac voltage, n is 0.45-0.85. The composite insulators are superior in external insulation selection in high altitude and heavy polluted areas. The relative error between the field test results and laboratory test results is less than 8%, so the research results obtained in the laboratory can be applied to engineering design.
38354
Yunpeng Liu et.al
Icing flashover characteristics and discharge process of 500 kV AC transmission line suspension insulator strings
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 434 – 442
The icing flashover characteristics and discharge processes of 500 kV ac transmission line long insulator strings energized in the ice accretion were studied. The influence of pollution and grading rings (including simulated conductor) on heavy ice-covered insulators’ flashover voltage were considered in this paper. Based on the artificial icing test results, it was found that 1) under the severe icing conditions and three salt deposit density (SDD) levels of PSDD=0.1, 0.05, 0.025 mg/cm2, compared with 500 kV transmission line rated phase to ground voltage, the flashover voltages of 28 units XWP2-160 porcelain double-shed insulator are 20.5% lower, 13.1% lower and 2.3% higher respectively; and the values of the FXBW4-500/160 composite insulator are 18.7% lower, 12.0% lower and 4.3% higher respectively. 2) equipped with the given grading ring and simulated conductor the icing flashover stress of 28 units XWP2-160 is lower than those without grading ring and simulated conductor under the three pollution degrees. The discharge process of the icing flashover and relevant factors were investigated also, which shows that 1) the locations of the air gaps on icing insulators are not completely random. 2) arcs on long insulator strings require more time to reach a critical length, hence, the arc propagation might be easily influenced by the decreasing of melted water conductivity and ice shedding than short insulator strings.
38355
Volat C. et.al
Monitoring leakage current of ice-covered station post insulators using artificial neural networks
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 443 – 450
This paper presents the analysis of leakage current evolution of an ice-covered station post insulator during a melting period using artificial neural network (ANN) models. The tests, carried out under wet-grown ice regime for different experimental conditions, showed that the permanent establishment of white arcs, identified as “permanent regime” led to flashover in the large majority of the cases,. Based on these observations, the development of a monitoring methodology aimed at forewarning the approach of the leading white arc during melting periods is proposed. The monitoring methodology uses different ANNs in order to predict the appearance of the white arc based on the identification, classification and analysis of the occurrence frequency of electric discharges. The results show that the ANN monitoring model developed is able to predict the onset of permanent regime under various experimental conditions. Hence, it was found that the delay between the permanent regime onset prediction delivered by the ANN model and its realization is 9 minutes on average. These results confirm that the proposed ANN model could be used as part of a monitoring system for post insulators during icing events for protection against potential flashover hazards.
38356
Sabri Y.
Application of identification methods for predicting the flashover voltage of contaminated insulators covered with ice
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 451 – 457
The arc characteristics on contaminated insulator surfaces covered with ice were investigated. The arc constants (A, n), as well as the ac re-ignition parameters (K, b) were determined using a simplified cylindrical physical model. Based on identification methods, a new approach for calculating the residual voltage is introduced. These results will serve to extend the previous mathematical model developed at CIGELE for its application to predicting the flashover voltage of contaminated insulators covered with ice. The model was successfully applied to a five-unit IEEE standard insulator string, and the calculated results were in good agreement with the experiments.
38357
Farokhi S.et.al
Experimental investigation of the process of Arc propagation over an ice surface
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 458 – 464
In this paper, some of the characteristics of an arc propagating over an ice-covered insulator surface were investigated. Special attention was paid to the arc root and channel characteristics. All experiments were performed on a simplified physical model to simulate real ice-covered insulators. From the obtained results, based on a set of time-resolved measurements of a surface discharge, some important characteristics, namely arc foot geometry and channel diameter were observed. Possible mechanisms controlling these variations are discussed. An empirical model, accounting for arc propagation pattern on an ice surface, is proposed. The paper contains a substantial amount of new material with a view of closing some major gaps in the present state of knowledge of ice surface flashover.
38358
Yong Liu & Du B.X
Recurrent plot analysis of leakage current on flashover performance of rime-iced composite insulator
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 465 – 472
Due to the wide application of composite insulators in the power industry, the insulator performance is challenged by various environments. To determine the flashover performance of rime-iced composite insulator, laboratory investigation was carried out in an artificial climate chamber to simulate different rime-ice morphology on the insulator surface. The configuration and characteristics of the rime-ice were demonstrated to establish the relationship between the rime-ice parameters and the flashover performance. In accordance with the discharge phenomena, the transition of leakage current (LC) until the flashover was analyzed by using a recurrent plot approach. After extracting the high frequency components by using a wavelet transform technique, the LC just before the flashover was extended to m dimensional phase space based on a phase space reconstructed method. The recurrent plot was obtained to reveal the non-linear characteristics of LC for identifying the dynamic behaviors on the insulator surface. It is shown that the propagation and properties of the discharges can be graphically projected on the topological structure of recurrent plot as a function of the rime-ice parameters. The process and underlying mechanism of flashover performance of rime-iced composite insulator can be visually reflected by the recurrent plot and the quantitative indicators of LC.
38359
Zhang X. et.al
Increased energy in stable dry-band arcs due to length compression
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 473 - 480
The occurrence of dry-band arcs on outdoor composite insulators can degrade the polymeric materials’ surface and ultimately may lead to insulator failure. The degradation processes are generally considered as aging effects occurring over long periods of time, from years to decades. In this paper, it is shown that if a stable dryband arc is physically compressed in length by external forces, such as electrolyte deformation due to wind or gravity, the arcing activities will become more severe. This in turn, may accelerate the degradation into a short time-frame hazard. A series of experiments are carried out to investigate the electrical characteristics of the arcs as they become compressed. In this case experiments are performed on silicone rod insulators at controlled angles to the horizontal. Rapid aging is observed after such events. Measurements of arcing period, peak current, and arc resistance during the arcing compression process are analyzed. Based on the experiments, a `Double Sinusoidal Model’ is developed to simulate the current-voltage characteristics of dryband arcing during its compression. Both experiment and simulation show that arc power, arc energy and corresponding energy density will dramatically increase if arc compression occurs, which may lead to more rapid and serious damage on composite insulator surfaces than is experienced otherwise. It is suggested that aggressive erosion events may occur in short periods of time within extended test regimes or entire service histories.
38360
Xingliang Jiang et.al
Evaluating the safety condition of porcelain insulators by the time and frequency characteristics of LC based on artificial pollution tests
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 481 – 489
Leakage current (LC) measurement is one of the effective methods for analysis of polluted insulators. But the traditional evaluation methods do not combine well the time-domain with frequency-domain characteristics of LC. In order to evaluate the safety condition of polluted insulators more effectively, an artificial neutral network (ANN) based method was developed in this paper. Firstly, a large number of artificial pollution tests for IEC standard suspension insulators were investigated under different relative humidity (RH) and salt deposit density (SDD). Then, based on the experimental data, the characteristics of LC were analyzed in both time-domain and frequency-domain. The results showed that the peak values of the LC (Ih ) has no relation with SDD when the RH is low ,but when the RH is high, the Ih increases with the increase of SDD; the phase difference (θ) between LC and applied voltage decreases with the increase of RH, the LC becomes inductive when strong local arc occurs; the total harmonic distortion (THD) of LC increases slowly with the increase of RH when the pollution is light, but decreases firstly, then increases with the increase of RH when the pollution is middle or heavy level, the value reaches to minimum when the RH is about 80%. Consequently, Ih, (θ) and THD were proposed as characteristic parameters to evaluate the safety condition of polluted insulators. Finally, an ANN with fuzzy output was developed to evaluate the safety condition of polluted insulators. The input parameters of the ANN were Ih, (θ) and THD, while the output parameters were fuzzified into four fuzzy subsets, the capability of ANN was validated by 8 pairs of testing samples, and the effects of SDD and RH on the performance of insulators were discussed.
38361
Jingyan Li et.al
Use of leakage currents of insulators to determine the stage characteristics of the flashover process and contamination level prediction
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 490 – 501
In order to improve the reliability of power transmission lines, one of the key issues is to reduce the hazard of contamination flashovers. Presently, the most efficient way is to clean (or replace) the heavily polluted insulators. The leakage current is the critical online quantity that can be detected. A number of laboratory experiments on 35 kV voltage class ceramic and glass insulators show that the leakage current fully reflects the entire process of contamination flashover development. The test results reveal that the process can be classified into three stages, i.e., security stage, forecast stage and danger stage. The results, that were duplicated several times, are based on three characteristics of the leakage current, i.e., the root-mean-square value, waveforms, and power spectrum estimation. In addition, the boundaries of the three stages in both time domain and power spectrum domain are also determined. All these can be used for the stage pre-warning of contamination flashovers. The security stage is most important since it precedes the contamination flashover sufficiently. The three characteristics of the leakage current in the security stage are proposed as the inputs of a neural network model together with the operating voltage, and the relative humidity in order to determine the equivalent salt deposit density (ESDD) of the insulators. The comparison of the simulated and actual (measured) results demonstrates that the ESDD prediction model has a very low relative error if the training data and the testing data both come from the security stage. The application of this research results in (1) optimal ESDD prediction inputs and (2) sufficient pre-warning time before the ultimate contamination flashover.
38362
Kordkheili H.H.et.al
Determining the probability of flashover occurrence in composite insulators by using leakage current harmonic components
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 502 – 512
Flashover of contaminated insulators in polluted areas is one of the most important factors influencing the operation of transmission and distribution lines and substations. Hence predicting an approaching flashover is of a great importance. In this paper, a new method and criteria have been proposed to predict the flashover occurrence of SIR composite insulators and its probability by using leakage current harmonic component. The tests were performed on various profiles of artificially polluted SIR insulators under clean fog condition. It is proposed that an important index is the ratio of 5th harmonic component to the 3rd for which the operational and critical limits have been determined. The probability of flashover occurrence has also been calculated by geometric distribution. Only the measurements of a minimal set of parameters are required. The presented criteria can be used to optimally schedule overhead lines maintenance teams and to develop proper Condition-Based Monitoring Systems (CBMS). Experimental results illustrate high performance of this approach.
38363
Heger G.et.al
A comparative study of insulator materials exposed to high voltage AC and DC surface discharges
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 513 – 520
An experimental study was conducted, using the Inclined Plane Test method to determine the performance of typical power line insulator materials: RTV (Room Temperature Vulcanized) silicone rubber coated porcelain, HTV (High Temperature Vulcanized) silicone rubber and EPDM rubber. The constant voltage method was employed to evaluate the performance of the above samples when energized by ac and dc (both polarities) voltages. The relative performance of the different materials and the effect of the voltage types were investigated. The results show that the RTV silicone rubber coating exhibits the least erosion for ac voltage but shows extensive erosion in the case of negative dc voltage. The HTV silicone rubbers exhibit only minimal erosion when exposed to ac test voltage, but develop strong erosion under positive dc voltage, which can result in sample failure. EPDM experiences the least erosion for a negative dc voltage, but shows maximum erosion severity for ac voltage.
38364
Bruce G.P.et.al
Performance of silicone rubber in DC inclined plane tracking tests
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 521 – 532
The inclined plane tracking and erosion test IEC-60587 is not specified for DC testing. A dc test has been developed from the current ac standard and three formulations of silicone rubber tested. These materials were tested under three voltage levels (2.3, 2.7 and 3.2 kV) for both polarities. Positive dc tests have the highest average and peak leakage current and exhibit a higher degree of surface damage. The observed surface degradation pattern is heavily dependant on polarity. Consistently higher levels of erosion have been observed in the higher voltage positive cases. Erosion of the surface always starts at the bottom electrode, and spreads toward the top electrode. Puncturing of the 6 mm thick samples or deep erosion over more than half the distance between electrodes has only been observed under 2.7 and 3.2 kV positive polarity tests. Results have been analysed using a variety of leakage current analysis techniques going beyond the criteria specified in the original ac standard. The low-frequency behaviour of the leakage current was monitored using a 15 sample per second current recorder. The leakage current magnitude is investigated in a case study and is shown to follow a normal distribution. Reversing the polarity of tests shows the leakage current seen in a test is largely independent of the surface degradation pattern present, but the surface degradation pattern over the first three hours may dictate the morphology of ensuing deep erosion.
38365
Schmidt L.E.et.al
Tracking and erosion resistance of high temperature vulcanizing ATH-free silicone rubber
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 533 - 540
Traditionally aluminum trihydrate (ATH) is added to high-temperature vulcanized (HTV) silicone rubber for outdoor insulation applications to improve flame retardancy and the electrical tracking and erosion performance. In this work, the flammability of ATH-free HTV silicone rubber formulations were evaluated by the UL94 vertical burning test. The most promising candidates, as well as reference formulations filled with silica or silica/ATH only, were then evaluated by the inclined plane tracking and erosion test at 4.5 kV. The best result was obtained by silicone rubber containing 100 phr silica and 15 phr melamine cyanurate. It was suggested that this was a result of the arc quenching ability of the melamine hence extinguishing the electrical arc. If the filler level was too high, resulting in poor dispersion, the resistance to tracking and erosion was significantly reduced. Thus formulating a HTV silicone rubber with good tracking and erosion resistance is a balance between having a high enough filler content, while still maintaining a good dispersion of the particles in the polymer matrix, as well as good bonding between the particles and the matrix.
38366
Du B.X.& Liu H.J.
Effects of atmospheric pressure on tracking failure of gamma-ray irradiated polymer insulating materials
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 541 – 547
With the increasing application of electric and electronic devices in space and nuclear power stations, the polymer insulation materials are inevitably exposed to various kinds of environments. As technology advances, increasing demands on the reliable operation under various operating and environmental conditions are made on materials and components. Therefore, it is important to investigate the influence of radiation on polymeric insulating materials used under the combined environments. This paper describes the effects of atmospheric pressure and gammaray irradiation on tracking failure of polybutylene naphthalate (PBN), polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) by applying a DC pulse voltage. PBN, PET and PBT were irradiated in air up to 100 kGy and then up to 1000 kGy with a dose rate of 10 kGy/h by using a 60Co gamma-source. The effects of total dose of irradiation and atmospheric pressure on the time to tracking failure and discharge quantity were discussed. Obtained results show that, with increasing the total dose, the time to tracking failure increased with PBN and PET, but decreased with PBT. With decreasing the atmospheric pressure, the time to tracking failure increased with PBN, PET and PBT. While increasing the total dose, the discharge quantity decreased with PBN and PET, but increased with PBT. With decreasing the atmospheric pressure, the discharge quantity increased with PBN and PET, but decreased with PBT. The experimental results suggest that the chemical structure of the polymeric insulating materials plays a main role in the result of radiation reaction, which is related to cross-linking and degradation reaction.
38367
Du B.X.et.al
Application of nonlinear methods in tracking failure test of printed circuit boards under reduced pressure
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 548 - 554
In high-altitude regions, printed circuit boards are affected by both low pressure and contamination, which may lead to discharge and even the failure of electrical devices. From the viewpoint of safety and reliability, it is necessary to investigate the effects of the pressure on tracking failure of contaminated printed circuit boards. However, the tracking failure is a nonlinear and indeterminate process which results in the dispersity of experimental results. This paper proposes two nonlinear methods, including fractal dimension of tracking pattern and recurrence plots of discharge current, to analyze the phenomena and mechanism of tracking failure under reduced pressures. The experiments were carried out in a decompression chamber, with the pressure reducing from 102.74 kPa to 0.6 kPa. The test sample was made by printing a pair of copper foil electrodes onto a glass-cloth-base epoxy resin laminate with the insulation distance from 500 µm to 100 µm. The contamination was simulated by a droplet of NH4Cl electrolyte with the resistivity of 4 Ω·m. The time to tracking failure, the fractal dimension of tracking patterns and the recurrent plot of discharge currents were obtained as functions of the pressure and the insulation distance. The results reveal that the nonlinear methods can give a good identification of the surface morphology and the underlying mechanism in the tracking test. Effects of the pressure and insulation distance on the tracking failure were quantitatively reflected with the fractal dimension of tracking patterns and the recurrent plot of discharge currents.
38368
Bin Ma et.al
Evaluating resistance of polymeric materials for outdoor applications to corona and ozone
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 555 – 565
Paper presents a review discussing methods of determination the resistance to corona discharges and ozone of polymeric materials for applications in outdoor insulation. It also describes a part of international activities within CIGRE WG D1.01 aiming to develop suitable methodology for the testing, which includes designing the necessary test arrangement, defining test conditions and finally exemplifying results of the treatment by monitoring changes of electrical, mechanical and structural properties of some materials.
This
38369
Fujii O.et.al
Vibration of a water droplet on a polymeric insulating material subjected to AC voltage stress
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 566 – 571
The behavior of a water droplet on a silicone rubber plate was observed with a high-speed camera under ac voltage application. It was confirmed that a water droplet vibrated and that a remarkable deformation from the original droplet form occurred at the mechanical resonance frequency. Vibration frequency of an uncharged water droplet was double the frequency of the applied voltage. On the contrary, in the case of an artificially charged droplet, vibration frequency was the same with that of the applied voltage. A macroscopic mechanical model was devised, to which the experimental data were well correlated. Flashover voltage via the water droplet was also measured. Lower flashover voltage was obtained at the mechanical resonance frequency.
38370
Wenxia Sima et.al
Experiments and analysis of sand dust flashover of the flat plate model
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 572 – 581
The influence of sand dust on the electrical discharge characteristics of outdoor insulation has drawn worldwide attention. Based on tests on the typical flat plate model, this paper presents research on the flashover characteristics of outdoor insulation in sand dust environment under ac and dc voltages, by means of which the effects of wind velocity, charge of sand particles, sand deposit on insulator and moisture content of sand particles on the flashover process are obtained. The test environment of the flat plate model is classified into sand-wind and sand deposit environments. In the sand-wind environment, wind velocity has remarkable influence on the ac and dc flashover voltages of the flat plate model while the sand and the charge of sand particles have little influence. In the sand deposit environment, the ac and dc flashover voltages of the flat plate model are influenced by the sand deposition density and the moisture content of sand particles. Moreover, according to the record of the flashover process and the calculation of the change of the electric field distribution during this process, the flashover mechanism is analyzed, which shows that the region without sand and the leakage current play important roles in the flashover of the flat plate model in the sand dust environment.
38371
Abderrazzaq M.H
The impact of ionic hydration on water absorption by composite insulation
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 582 – 587
The importance of ionic hydration phenomenon in water absorption is introduced. A set of composite samples, fabricated from polyester resin and glass fiber, are exposed to a number of aqueous solutions. The change in sample weight of such composites, as a result of water absorption, is investigated. The variation of water pick up is determined as a function of ionic solution type, concentration and applied voltage. The time distribution of absorbed moisture by composite specimens is calculated from the measured values. The results, presented in this paper, are based on experimental work conducted under different conditions. Moisture absorption rates, attributed to the ionic hydration of various salt solutions, are compared with that of deioniozed water for all studied cases. The impact of barriers, in hindering the water to diffuse throughout the whole sample, is studied by monitoring the salt crystal deposits that result after drying the sample for enough time. The images of residual ionic crystals assist in determining the areas, where the moisture is distributed inside composite samples.
38372
Burks, B.et.al
Failure prediction analysis of an ACCC conductor subjected to thermal and mechanical stresses
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 588 – 596
In this work, the Aluminum Conductor Composite CoreTM (ACCC) was numerically investigated to evaluate stress distributions when subjected to thermal and mechanical loads. The thermal analysis was conducted to simulate the cooling cycle of the rod from 250°C to room temperature. Three types of mechanical loads were considered, namely axial tension, small bending, and large bending conditions. This was done to predict potential mechanical failure modes, which could reduce the short term performance of the conductors. It has been shown that the magnitudes of the residual thermal stresses in the composite core are low and insufficient to create internal mechanical damage during manufacturing. As expected, the axial tension analysis indicated that under extreme axial tensile loads the ACCC rod will fail catastrophically. The most important results were obtained through the bending analysis, especially under large displacement conditions. Under these conditions the ACCC rod will develop mechanical compressive damage in its carbon fiber/epoxy section if the rods are bent around relatively small mandrels either during transportation or installation.
38373
Ramirez I et.al
Analysis of temperature profiles and protective mechanism against dry-band arcing in silicone rubber nanocomposites
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 597 – 606
The paper discusses the mechanism by which nanofillers improve the erosion resistance of silicone rubber nanocomposites under simulated conditions of dry band arcing. Various micro-nano composites are studied, including microfiller, nanofiller, combinations of both, and with a commercial surfactant to improve the dispersion of the nanofiller. The thermal conductivity of the composites, measured using a standard method, shows higher thermal conductivity when the nanofiller is well dispersed. A thermal model is developed and solved with finite element method (FEM) to examine the temperature profile in the modelled nanocomposites under laser heating, which simulates the hot spot from dry band arcing. The hot spot is compared to the measured temperature profile by an infrared camera. SEM, EDAX, and XRD techniques are used to analyze the thermally decomposed silicone residue after laser heating to elucidate the protective mechanism in the silicone rubber nanocomposites.
38374
Raetzke S.& Kindersberger J.
Role of interphase on the resistance to high-voltage arcing, on tracking and erosion of silicone/SiO2 nanocomposites
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 607 - 614
In this study a two kinds of silicone/SiO2 nanocomposites were tested with respect to their resistance to high-voltage arcing, the resistance to tracking and erosion and their TGA performance. The silicones with filler type F1 show a high improvement of the resistance to high-voltage arcing and the resistance to tracking and erosion at very low filler contents. Furthermore, a maximum resistance to high-voltage arcing is observed for these nanocomposites at a filler content of 5% wt. In contrast to that the silicones with filler type F2 show no significant improvement for both resistances. The effects are explained by the ratio of interphase to matrix material, which is estimated by the Interphase Volume Model. The thermogravimetric analysis (TGA) shows that the resistance to thermal degradation is significantly higher for the silicones with filler type F1 already at a filler content of 0.5 wt.% compared to the material without any fillers. The resistance to thermal degradation for the materials with filler type F2 is significantly lower. This result is also explained by the high interphase content.
38375
Venkatesulu B.& Thomas M.J.
Erosion resistance of alumina-filled silicone rubber nanocomposites
IEEE Transactions on Dielectrics and Electrical Insulation, Vol.17; No.2; April 2010; 615 – 624
This paper deals with the experimental studies on the erosion resistance of low weight % alumina-filled nanocomposites and highly filled microcomposites. Erosion resistances of 2.5 % and 4 % by weight alumina-filled silicone rubber nanocomposites and 5 %, 10 %, 15 %, 20 % and 30 % by weight ATH filled microcomposites have been compared. For the performance comparison, inclined plane tracking and erosion resistance tests have been done on the silicone rubber samples. The results obtained indicate that the performance of 4 % by weight nanocomposite is comparable to that of the 30 % by weight ATH composite. Thermo gravimetric analysis shows that the thermal stability of the nanocomposite is better than the microcomposite even at low concentration of the nanofillers studied. The above encouraging results can be mainly attributed to the better thermal stability of the nanocomposite due to the large increase in the number of nanofillers, significant quantity of polymer chains with restricted mobility at the interface between the polymer and the fillers and better physical bonding between the nanofillers and the polymer matrix. Interestingly, formation of entirely different types of physical micro structures, viz., lump type and honey comb type have been observed at the degraded portions of the microcomposites and the nanocomposites respectively which also supports the above observation. It is also noticed that the ratio of r.m.s to average leakage current is a reflection of the degree of erosion of the sample which in turn seems to be a good indicator to assess the degradation performance of materials.
38376
Venkatesulu B.& Thomas M.J.
Corona aging studies on silicone rubber nanocomposites
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 625 - 634
In EHV and UHV power transmission lines, corona could occur even on well designed transmission line hardware and insulators especially under wet conditions. Corona if allowed to occur continuously can significantly damage the polymeric insulators used in such lines in the long run. This paper presents the experimental results of corona aging studies conducted on unfilled silicone rubber as well as filled silicone rubber nanocomposites. Corona aging studies were conducted on silicone rubber samples with filler concentrations of 0, 1, 2 and 3% by wt of nanosilica for 25 h and 50 h. Needleplane electrode geometry has been used to create the corona on the samples. Different characterization techniques such as Scanning Electron Microscopy, Energy Dispersive X-ray analysis, Hydrophobicity, Fourier Transform Infrared Spectroscopy, and Optical Profilometry have been used to assess the relative performance of the samples with respect to corona aging. Results indicate that at 3 wt%, the performance of the nanocomposite is much better than the unfilled silicon rubber which can be attributed to the modifications in the material caused by the size factor of the filler.38377
Xingyi Huang et.al
Influence of nanoparticle surface treatment on the electrical properties of cycloaliphatic epoxy nanocomposites
IEEE Transactions on Dielectrics and Electrical Insulation, Vol. 17; No.2; April 2010; 635 - 643
This experimental study reports the influence of the surface treatment of silica nanoparticles on the morphology and electrical properties of epoxy composites. (3-Glycidoxypropyl)methyldiethoxysilane was used as a silane coupling agent for the surface treatment of the silica nanoparticles. It was found that the incorporation of the silane onto the surface of silica nanoparticles not only improved the dispersion of the nanoparticles in epoxy, but also improved the electrical properties as compared with the composites filled with unsurface-treated nanoparticles. The surface treatment makes it possible to increase volume resistivity, dielectric strength, and provides an excellent approach able to reduce the dielectric loss of the nanocomposites. It is concluded that the improved properties could be directly ascribed to the good dispersion and special physicochemical characteristics of the surface-treated nanoparticles in the polymer matrix.
38378
Montilla-DJesus M.E.et.al
Optimal Operation of Offshore Wind Farms With Line-Commutated HVDC Link Connection
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 504 – 513
This paper aims to calculate the optimal operation of offshore wind farms (OWF) working with wind turbines based on doubly fed induction generator (DFIG) technologies, and with a high-voltage dc transmission connection. The objective of the optimization problem is to maximize the active power output of the arrangement, while considering certain factors, i.e., the restrictions imposed by the available wind power, the capability curve of the DFIG, the dc-link model, and the operative conditions. The accomplishment of this aim implies setting, adjusting, and operating the system under study in order to produce a reliable and cost-efficient electric energy supply. A realistic simulation test case is performed to evaluate the proposed method, and the optimal operation analysis takes into account different wind speeds and high-voltage dc-link lengths. The results show the effectiveness of the proposed method, demonstrating the advantages of using the reactive control performed by the DFIG to manage the operational requirements of the dc link.
38379
Rahimi M. & Parniani M
Transient Performance Improvement of Wind Turbines With Doubly Fed Induction Generators Using Nonlinear Control Strategy
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 514 – 525
This paper first discusses dynamic characteristics of wind turbines with doubly fed induction generator (DFIG). Rotor back electromotive force (EMF) voltages in DFIG reflect the effects of stator dynamics on rotor current dynamics, and have an important role on rotor inrush current during the generator voltage dip. Compensation of these voltages can improve DFIG ride-through capability and limit the rotor current transients. It is found that the electrical dynamics of the DFIG are in nonminimum phase for certain operating conditions. Also, it is shown that the dynamics of DFIG, under compensation of rotor back EMF and grid voltages, behave as a partially linearizable system containing internal and external dynamics. The internal and external dynamics of DFIG include stator and rotor dynamics, respectively. It is found that under certain operating conditions, the internal dynamics, and thus, the entire DFIG system becomes unstable. This phenomenon deteriorates the DFIG postfault behavior. Since the DFIG electrical dynamics are nonlinear; the linear control scheme cannot properly work under large voltage dips. We address this problem by means of a nonlinear controller. The proposed approach stabilizes the internal dynamics through rotor voltage control, and improves the dynamic behavior of the DFIG after clearing the fault.
38380
Cimuca G.et.al
Design and Control Strategies of an Induction-Machine-Based Flywheel Energy Storage System Associated to a Variable-Speed Wind Generator
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 526 – 534
Flywheel energy storage systems (FESSs) improve the quality of the electric power delivered by wind generators, and help these generators contributing to the ancillary services. Presently, FESSs containing a flux-oriented controlled induction machine (IM) are mainly considered for this kind of application. The paper proposes the direct torque control (DTC) for an IM-based FESS associated to a variable-speed wind generator, and proves through simulation and experimental results that it could be a better alternative. This DTC application entails two specific aspects: 1) the IM must operate in the flux-weakening region, and 2) it must shift quickly and repeatedly between motoring and generating operation modes. DTC improvement for increasing the FESS efficiency, when it operates at small power values, is discussed. Some aspects concerning the flywheel design and the choice of the filter used in the FESS supervisor are also addressed.
38381
Li Wang & Zan-Jia Chen
Stability Analysis of a Wave-Energy Conversion System Containing a Grid-Connected Induction Generator Driven by a Wells Turbine
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 555 – 563
This paper presents the dynamic-stability analyzed results of both dynamic simulations and steady-state performance of a wave-energy power generation system containing a grid-connected induction generator (IG) driven by a Wells turbine. The stator windings of the IG are connected directly to a power grid through a step-up transformer and a transmission line. A d-q axis equivalent-circuit model is employed to establish the IG, the transmission line, and the grid to derive the complete dynamic equations of the studied system under three-phase balanced loading conditions. A frequency-domain approach based on eigenvalue analysis and a time-domain scheme based on nonlinear-model simulations are both carried out to systematically determine the dynamic stability of the studied system under various operating conditions. It can be concluded from the simulation results that the studied wave-energy power generation system subject to different disturbance conditions can maintain stable operation.
38382
Munteanu I et.al
Hardware-in-the-Loop-based Simulator for a Class of Variable-speed Wind Energy Conversion Systems: Design and Performance Assessment
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 564 – 576
This paper focuses on the design, building, error evaluation, and performance assessment of a physical simulator for a variable-speed wind energy conversion system (WECS). Such simulator, dedicated to control algorithms validation, must replicate the dynamical behavior of the WECS physically in real time. To this end, software parts, which model subsystems of the plant, and hardware parts, taken as they are from the plant, are closed-loop connected, thus implementing a hardware-in-the-loop (HIL) simulator. The simulator interacts with a software-simulated environment-in this case, the wind velocity-in order to run experiments under controllable conditions. Controllers to be tested interact directly with the hardware part of the simulator, thus better approaching the behavior of the real-world WECS. A complete grid-connected generation chain employing a horizontal-axis fixed-pitch three-bladed rotor permanent-magnet-synchronous-generator-based WECS is chosen as example for the design and performance assessment of an HIL simulator, both in frequency and time domain.
38383
Callaway D.S.et.al
Sequential Reliability Forecasting for Wind Energy: Temperature Dependence and Probability Distributions
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 577 – 585
Sequential wind simulation models have been developed to forecast effective load-carrying capability (ELCC), but they produce data that follow a Gaussian distribution, which can be considerably different from real wind-speed distributions, and they do not explicitly model the influence of temperature on the evolution of wind speed. The latter issue is of significant importance considering the strength of correlation between electricity load and temperature and the influence electricity load shapes have on system reliability. This paper presents a new approach to reliability estimation of wind facilities that models wind-speed distributions nonparametrically and includes the effect of temperature on the evolution of wind speed. A relatively long tall tower anemometer dataset is then used to test whether or not the model output produces ELCC distributions that are statistically similar to observed distributions. Results indicate that, relative to temperature independent models, temperature-dependent time-series models are better at both short-term wind-speed forecasting and long-term reliability forecasting. Results also show that reliability forecasts are relatively unaffected by the shape of the wind-speed distribution. Finally, it is apparent that model performance is robust to variation in the average wind power in the years used for model parameterization.
38384
Abad G. et.al
Direct Torque Control for Doubly Fed Induction Machine-Based Wind Turbines Under Voltage Dips and Without Crowbar Protection
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 586 – 588
This letter proposes a rotor flux amplitude reference generation strategy for doubly fed induction machine based wind turbines. It is specially designed to address perturbations, such as voltage dips, keeping controlled the torque of the wind turbine, and considerably reducing the stator and rotor overcurrents during faults. In addition, a direct torque control strategy that provides fast dynamic response accompanies the overall control of the wind turbine. Despite the fact that the proposed control does not totally eliminate the necessity of the typical crowbar protection for this kind of turbines, it eliminates the activation of this protection during low depth voltage dips.
38385
Lee S et.al
New Power Quality Index in a Distribution Power System by Using RMP Model
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 1204 – 1211
In this paper, a new power quality index (PQI), which is directly related to the generation of distortion power from nonlinear harmonic loads, is introduced to determine their harmonic pollution ranking in a distribution power system. The electric load composition rate (LCR) and the total harmonic distortion (THD) for the estimated currents on each harmonic load are used to define the proposed PQI. The reduced multivariate polynomial (RMP) model with one-shot training property is applied to realize the PQI. Then, the ranking of distortion power for each nonlinear load, which has adverse effect on the entire system, is determined. It is proven that the relative ranking based on the PQI matches that based on the distortion power directly computed from each harmonic load.
38386
Peiyuan Chen et.al
ARIMA-Based Time Series Model of Stochastic Wind Power Generation
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 667 – 676
This paper proposes a stochastic wind power model based on an autoregressive integrated moving average (ARIMA) process. The model takes into account the nonstationarity and physical limits of stochastic wind power generation. The model is constructed based on wind power measurement of one year from the Nysted offshore wind farm in Denmark. The proposed limited-ARIMA (LARIMA) model introduces a limiter and characterizes the stochastic wind power generation by mean level, temporal correlation and driving noise. The model is validated against the measurement in terms of temporal correlation and probability distribution. The LARIMA model outperforms a first-order transition matrix based discrete Markov model in terms of temporal correlation, probability distribution and model parameter number. The proposed LARIMA model is further extended to include the monthly variation of the stochastic wind power generation.
38387
Karki R. et.al
Reliability Evaluation Considering Wind and Hydro Power Coordination
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 685 – 693
Wind energy application in electric power systems continues to increase globally. The contribution of wind farms to the overall system reliability is limited by the uncertainty in power output from these highly variable energy sources. The ability of a power system to absorb available wind energy and maintain the system reliability and stability is reduced as the wind penetration in the system is increased. It therefore becomes important to coordinate the operation of wind power with fast responding conventional generating units. Hydro facilities with energy storage capability can alleviate the impact of wind power fluctuations and also contribute to system adequacy. A methodology for an energy limited hydro plant and wind farm coordination is developed using a Monte Carlo simulation technique considering the chronological variation in the wind, water and the energy demand. The IEEE four-state model is incorporated in the developed technique to recognize the intermittent operation of hydro units. The proposed approach is applied to the IEEE-RTS, and quantitative assessment of reliability benefits from effective utilization of wind and water resources are conducted through a range of studies. The effects of major system parameters on the system adequacy are also investigated.
38388
Sioshansi R
Evaluating the Impacts of Real-Time Pricing on the Cost and Value of Wind Generation
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 741 – 748
One of the costs associated with integrating wind generation into a power system is the cost of redispatching the system in real-time due to day-ahead wind resource forecast errors. One possible way of reducing these redispatch costs is to introduce demand response in the form of real-time pricing (RTP), which could allow electricity demand to respond to actual real-time wind resource availability using price signals. A day-ahead unit commitment model with day-ahead wind forecasts and a real-time dispatch model with actual wind resource availability is used to estimate system operations in a high wind penetration scenario. System operations are compared to a perfect foresight benchmark, in which actual wind resource availability is known day-ahead. The results show that wind integration costs with fixed demands can be high, both due to real-time redispatch costs and lost load. It is demonstrated that introducing RTP can reduce redispatch costs and eliminate loss of load events. Finally, social surplus with wind generation and RTP is compared to a system with neither and the results demonstrate that introducing wind and RTP into a market can result in superadditive surplus gains.
38389
Emhemed A.S
Analysis of Transient Stability Enhancement of LV-Connected Induction Microgenerators by Using Resistive-Type Fault Current Limiters
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 885 - 893
In this paper an analytical method by which the transient stability of an induction machine is maintained regardless of the fault clearance times is introduced. The method can be applied in order to improve the transient stability of a large penetration of low-voltage (LV) connected microgeneration that can be directly interfaced by single-phase induction generators within domestic premises. The analysis investigates the effectiveness of using resistive-type superconducting fault current limiters (RSFCLs) as remedial measures to prevent the microgenerators from reaching their speed limits during remote faults, and hence improving their transient stability. This will prevent unnecessary disconnection of a large penetration of LV-connected microgeneration and thus avoiding the sudden appearance of hidden loads, and unbalanced voltage conditions. The minimum required value of a resistive element of RSFCL for mitigating the transient instability phenomena of LV-connected microgeneration based on the system and connected machine parameters is determined. The analytical method has been validated by conducting informative transient studies by using detailed models of a small microwind turbine with constant mechanical output interfaced directly within residential dwellings by a single-phase induction generator, a transient model of resistive superconducting fault current limiter (RSFCL), and a typical suburban distribution network with residential loads. All the models are developed in the time-domain PSCAD/EMTDC dynamic simulation.
38390
Albanna A.Z. & Hatziadoniu C.J
Harmonic Modeling of Hysteresis Inverters in Frequency Domain
IEEE Transactions on Power Electronics, Vol.25; No.5; May 2010; 1110 - 1114
This letter derives a closed-form analytical approximation of the output harmonic spectrum of a single-phase two-level inverter under the action of hysteresis current control. The analytical approach consists of first describing the error current as a triangular signal of variable duty cycle and frequency, and subsequently, deriving the Fourier transform of the complex envelope of the modulated triangular signal. The spectrum of the error current is given in terms of Bessel functions of the first kind. MATLAB/Simulink results on a half-bridge inverter are presented in this letter to demonstrate the validity and accuracy of the proposed model.
38391
Shuibao Guo et.al
Digital Sliding-Mode Controller For High-Frequency DC/DC SMPS
IEEE Transactions on Power Electronics, Vol.25; No.5; May 2010; 1120 – 1123
Digital control technique is becoming an attractive alternative for high-frequency switching mode power supply (SMPS). This paper introduces a fully synthesizable digital sliding-mode (SM) controller for high-frequency dc/dc SMPS. The proposed SM controller is associated with a digital pulsewidth modulation (DPWM) block to operate at constant and high switching frequency compared to already published approaches. The digital SM controller is experimentally validated by means of field-programmable gate array in a 4-MHz step-down converter with 10-bit analog-to-digital conversion (ADC) and 11-bit DPWM. Measured dynamic performances are superior to conventional digital controllers for dc/dc SMPS.
38392
Oettmeier M et.al
Dead-Beat Control Algorithm for Single-Phase 50-kW AC Railway Grid Representation
IEEE Transactions on Power Electronics, Vol.25; No.5; May 2010; 1184 - 1192
The control of four-quadrant converters (4QC) of traction vehicles fed by an ac railway grid has to meet very restrictive limitations with regard to harmonics and stability. The challenge is increased by continuously changing the position-dependent grid impedance and voltage harmonics already contained in the grid voltage. Testing a 4QC control in a lab, therefore, requires a railway grid representation that both emulates variable grid impedance and grid-voltage harmonics. The paper presents an innovative solution to this problem that employs a 4Q inverter with a suitably designed new control scheme. As the rated power is not high, compared to the traction vehicle fed, the control has to be effective, taking each switching event of the inverter into account. For the design of the control, a suitable simulation is needed, which is also presented in this paper. A comparison of simulation and measurement results is given, proving excellent results.
38393
Zarebski J.& Gorecki, K.
The Electrothermal Large-Signal Model of Power MOS Transistors for SPICE
IEEE Transactions on Power Electronics, Vol.25; No.5; May 2010; 1265 – 1274
In this paper, the isothermal model of power MOS transistors offered by the producer of these devices and the electrothermal model of these devices proposed by the authors are presented. The results of experimental verification of both the models are given as well.
38394
Yu Chen & Yong Kang
A Fully Regulated Dual-Output DC–DC Converter With Special-Connected Two Transformers (SCTTs) Cell and Complementary Pulsewidth Modulation–PFM (CPWM-PFM)
IEEE Transactions on Power Electronics, Vol.25; No.5; May 2010; 1296 – 1309
A dual-output dc-dc converter based on the complementary pulsewidth modulation is proposed to overcome the cross-regulation problem between the outputs. Using a special-connected two transformers cell, one operational period is divided into two complementary parts. One output branch gets the pulsewidth and is regulated by the duty cycle; the other output branch gets the complementary pulsewidth and is regulated by the PFM. Only one full bridge and several passive components are needed, but both the two outputs have the fully regulated abilities even in the no-load situation. Moreover, a full zero-voltage-switching (ZVS) range is achieved in all the switches without auxiliary circuits. Therefore, the proposed topology has compact structure, high switching frequency, high-power density, and high efficiency. The operation principle, ZVS conditions, and design considerations are presented in the paper. The analysis is verified by a 300 V input, and 24 V/10 A and 48 V/5 A outputs prototype.
38395
Akagi H. & Kondo R.
A Transformerless Hybrid Active Filter Using a Three-Level Pulsewidth Modulation (PWM) Converter for a Medium-Voltage Motor Drive
IEEE Transactions on Power Electronics, Vol.25; No.6; May 2010; 1365 – 1374
This paper presents a transformerless hybrid active filter integrated into a medium-voltage motor drive for energy savings. This hybrid filter is intended for line harmonic-current mitigation of the three-phase diode rectifier used as the front end of the motor drive. It is based on direct connection of a passive filter tuned to the seventh-harmonic frequency in series with an active filter using a three-level pulsewidth modulated (PWM) converter. This paper provides a theoretical discussion on voltage-balancing control of two split dc capacitors of the active filter. The 400-V 15-kW motor drive system is designed, constructed, and tested, which can be considered as a downscaled model from a medium-voltage motor drive without regenerative braking. Experimental results verify that the hybrid filter has the capability of satisfactory harmonic filtering and stable voltage balancing in all the load conditions.
38396
Volle F et.al
Thermal Management of a Soft Starter: Transient Thermal Impedance Model and Performance Enhancements Using Phase Change Materials
IEEE Transactions on Power Electronics, Vol.25; No.6; May 2010; 1395 – 1405
Adverse effects of starting-torque transients and high in-rush currents in induction motors are typically mitigated by employing electronically controlled soft starting voltages through silicon-controlled rectifiers (SCRs). However, the heat dissipation in the soft starter must be carefully managed in the design of motor drives. The objective of this study is both to address the heat dissipation in the soft starter by implementing analytical solutions to the heat diffusion equations inside the soft starter, and to investigate the use of a phase change material (PCM) based heat sink for thermal management of the device. The analytical modeling approach is, however, general, and can be applied to the solution of a range of thermal problems in power electronics. The transient analytical thermal model, based on the thermal quadrupole approach, allows a determination of the transient performance of a soft starter by evaluating the thyristor junction temperature. Predictions from the model are first compared to results obtained using a coupled thermal and electrical model based on a resistance/capacitance network approach. Experimental results obtained with the soft starter connected to a low-voltage 200 hp induction machine are then used to validate the model. Additionally, the performance improvement resulting from the use of a hybrid heat sink (plate fin heat sink immersed in a PCM) is evaluated and compared to a conventional air-cooled heat sink without a PCM under identical conditions.
38397
Bin Su & Zhengyu Lu
An Interleaved Totem-Pole Boost Bridgeless Rectifier With Reduced Reverse-Recovery Problems For Power Factor Correction
IEEE Transactions on Power Electronics, Vol.25; No.6; May 2010; 1406 – 1415
An interleaved totem-pole boost bridgeless rectifier with reduced reverse-recovery problems for power factor correction is proposed in this paper. The proposed converter consists of two interleaved and intercoupled totem-pole boost bridgeless converter cells. The two cells operate in phase-shift mode. Thus, the input current can be continuous with low ripple. For the individual cells, they operate alternatively in discontinuous current mode and the maximum duty ratio is 50%, which allows shifting the diode current with low di/dt rate to achieve zero-current switching off. Zero-voltage switching is achieved in the MOSFETs under low line input. Furthermore, the merits of totem-pole topology are inherited. The common-mode (CM) noise interference is rather low. And the potential capacity of bidirectional power conversion is retained. In brief, the conduction losses are reduced, reverse-recovery process is improved, and high efficiency is achieved. The interleaved totem-pole cell can also be applied to bidirectional dc/dc converters and ac/dc converters. Finally, an 800 W, 100 kHz experimental prototype was built to verify the theoretical analysis and feasibility of the proposed converter, whose efficiency is above 95.5% at full load under 90 V.
38398
Vargas R et.al
Predictive Torque Control of an Induction Machine Fed by a Matrix Converter With Reactive Input Power Control
IEEE Transactions on Power Electronics, Vol.25; No.6; May 2010; 1426 – 1438
This paper presents a new control method for a matrix-converter-based induction machine drive. A discrete model of the converter, motor, and input filter is used to predict the behavior of torque, flux, and input power to the drive. The switching state that optimizes the value of a quality function, used as the evaluation criterion, is selected and applied during the next discrete-time interval. Experimental results confirm that the proposed strategy gives high-quality control of the torque, flux, and power factor with a fast dynamic control response. The key implementation issues are analyzed in depth to give an overview of the realization aspects of the proposed algorithm.
38399
Bai H et.al
Experimental Comparison of Traditional Phase-Shift, Dual-Phase-Shift, and Model-Based Control of Isolated Bidirectional DC–DC Converters
IEEE Transactions on Power Electronics, Vol.25; No.6; May 2010; 1444 – 1449
Three different control algorithms, traditional single-phase-shift control, dual-phase-shift control (DPSC), and model-based phase-shift control (MPSC), are implemented in a hardware setup and compared for a full-bridge-based isolated bidirectional dc–dc converter. The differences among their dynamic performance and steady-state operations are quantitatively analyzed. Experimental results showed good agreement with theoretical analysis. MPSC showed the best dynamic performance, while DPSC can eliminate reactive power under light-load conditions.
38400
Mukherjee R et.al
Impact of a Frequency Modulated Pulsewidth Modulation (PWM) Switching Converter on the Input Power System Quality
IEEE Transactions on Power Electronics, Vol.25; No.6; May 2010; 1450 – 1459
In this paper, we show that a frequency modulated (FM) source of conducted emission has an adverse effect on a dc power system, although it is believed that frequency modulation of the interferer reduces such effects. Spread spectrum modulation is a commonly proposed technique of electromagnetic interference (EMI) reduction. It is often suggested that an FM pulsewidth modulation ramp be used in a voltage mode controlled dc–dc switching converter for reduction of conducted and radiated EMI. However, this paper shows that this technique is not as beneficial as is commonly perceived. The power quality standard MIL-STD 704, which is the origin of the EMI standard MIL-STD 461, puts restriction on several parameters other than the frequency spectrum of the disturbance, which is the only parameter that is specified in the EMI norms and tested in electromagnetic compatibility (EMC) tests. In this paper, we show that different interferers which are compatible to the same EMC limit, may affect the same power system differently. This difference is noticed if the other power quality parameters are considered. We have also mentioned that the actual benefit from spread spectrum modulation-based EMI reduction depends on the savings in printed circuit board (PCB) footprint area that we get by using a smaller filter. Through a numerical study, we have shown that such a method leads to only a negligible savings in PCB area in spite of significant EMI reduction. Moreover, this brings about a degraded performance on the other parameters that are not normally checked in EMI tests.
38401
Ma H et.al
Design and Analysis of Single-Stage Power Factor Correction Converter With a Feedback Winding
IEEE Transactions on Power Electronics, Vol.25; No.6; May 2010; 1460 – 1470
A new single-stage power factor correction (SSPFC) converter is proposed for the adapter application, which is composed of a flyback converter, a feedback winding and a front-end input current shaper. Through the feedback winding, a direct energy transfer path is configured to improve the conversion efficiency and alleviate the voltage stress across the bulk capacitor. Moreover, the feedback winding is connected to the input through only two diodes, which results in low conduction losses. Equations and configurations are given to design the input current-shaping inductor and the magnetizing inductor of the transformer, which are operated in the discontinuous conduction mode (DCM) and the DCM/ continuous conduction mode boundary mode respectively for well-shaped current waveform and reduced bulk capacitor voltage. The theoretical analysis of the converter is verified by two SSPFC prototype circuits with 19 V/90 W output. One prototype achieves a high efficiency of 90.3%, while complying with IEC 61000-3-2 Class D standard. With a different turns ratio design, the power factor can be further improved to 0.97 in another prototype.
38402
Axente, I. et.al
12-kVA DSP-Controlled Laboratory Prototype UPQC Capable of Mitigating Unbalance in Source Voltage and Load Current
IEEE Transactions on Power Electronics, Vol.25; No.6; May 2010; 1471 - 1479
This paper reports the development of a laboratory prototype of a fully digital DSP-controlled 12-kVA unified power quality conditioner (UPQC), capable of compensating for both the supply voltage and the load current imperfections. A fully digital controller based on the TMS320F2812 DSP platform is implemented for the reference generation as well as control purposes. The delay problem in the digital controller is overcome by application of a fast DSP, a compact control technique and proper flow of control steps in the DSP software. A phase-locked loop-less software grid synchronization method has been implemented for the effective operation of the UPQC under conditions of grid frequency variation. A sequence-based compensation strategy has been developed to compensate for balanced and unbalanced sags while accommodating the fact that the voltage injection capability of the UPQC is limited. The prototype UPQC power circuit, control features, and control algorithm along with experimental results are presented in this paper.
38403
Ambusaidi K et.al
New Circuit Topology for Fault Tolerant H-Bridge DC–DC Converter
IEEE Transactions on Power Electronics, Vol.25; No.6; May 2010; 1509 – 1516
This paper describes a new design for a fault tolerant H-bridge dc–dc converter. Fault tolerance is achieved using a multilevel converter topology in combination with a pulsewidth modulation control strategy allowing a large set of converter switching states to produce bidirectional power flows at any required output voltage. For a given converter open-circuit or short-circuit fault, all potential switch combinations are compared in terms of converter losses and output voltage harmonics to identify the most suitable switching combinations to achieve the prefault output voltage level. The fault tolerant ability of the proposed converter to recover the required output voltage is verified by both computer simulations and experimentally using a 1 kW laboratory set.
38404
Azcondo F. J et.al
Power Factor Correction Without Current Sensor Based on Digital Current Rebuilding
IEEE Transactions on Power Electronics, Vol.25; No.6; May 2010; 1527 – 1536
A new digital control technique for power factor (PF) correction is presented. The main novelty of the method is that there is no current sensor. Instead, the input current is digitally rebuilt, using the estimated input current in the current loop. The circuit measures the input and output voltage by means of low cost ad hoc analog-to-digital converters (ADCs). Taking advantage of the slow dynamic behavior of these voltages, almost completely digital ADCs have been designed, leaving only a comparator and an RC filter in the analog part. Avoiding measuring current can provide a significant advantage compared to analog controllers and this also helps to reduce the total cost. The ultimate objective is to obtain a low-cost digital controller that can be easily integrated as an intellectual property (IP) block into a field-programmable gate array, or an application-specific integrated circuit. The experimental results show a reasonably high PF, despite not measuring the input current, and therefore the feasibility of the method.
38405
Masihuzzaman M et.al
Steady-State Stability of Current Mode Active-Clamp ZVS DC–DC Converters
IEEE Transactions on Power Electronics, Vol.25; No.6; May 2010; 1546 – 1555
Active-clamp dc–dc converters are pulsewidth-modulated converters having two switches featuring zero-voltage switching at frequencies beyond 100 kHz. Generalized equivalent circuits valid for steady-state and dynamic performance have been proposed for the family of active-clamp converters. The active-clamp converter is analyzed for its dynamic behavior under current control in this paper. The steady-state stability analysis is presented. On account of the lossless damping inherent in the active-clamp converters, it appears that the stability region in the current-controlled active-clamp converters get extended for duty ratios, a little greater than 0.5, unlike in conventional hard-switched converters. The conventional graphical approach fails to assess the stability of current-controlled active-clamp converters due to the coupling between the filter inductor current and resonant inductor current. An analysis that takes into account the presence of the resonant elements is presented to establish the condition for stability. This method correctly predicts the stability of the current-controlled active-clamp converters. A simple expression for the maximum duty cycle for subharmonic free operation is obtained. The results are verified experimentally.
38406
Fang T et.al
Control Strategy to Achieve Input and Output Voltage Sharing for Input-Series–Output-Series-Connected Inverter Systems
IEEE Transactions on Power Electronics, Vol.25; No.6; May 2010; 1585 – 1596
This paper explores a new configuration for modular inverter systems, namely, input-series–output-series (ISOS) connected inverter systems, which are very suitable for high-input-voltage and high-output-voltage applications. The control objective of such systems is to achieve input voltage sharing (IVS) and output voltage sharing (OVS) among the constituent modules. This paper first reveals the relationship between IVS and OVS and points out that IVS and OVS can be simultaneously achieved only by the application of a compound strategy, which involves controlling IVS as well as controlling the magnitudes or phases of the modules’ output voltages. Then, a practical implementation of the compound strategy, which combines a method of IVS with synchronization of the output phase angles, is proposed. An analysis of the decoupling of the two control loops, along with the detailed description of their design, is also presented. Finally, experimental results are presented to verify the theoretical analysis.
38407
Yao Z et.al
Seamless Transfer of Single-Phase Grid-Interactive Inverters Between Grid-Connected and Stand-Alone Modes
IEEE Transactions on Power Electronics, Vol.25; No.6; May 2010; 1597 - 1603
This paper presents a novel seamless transfer of single-phase grid-interactive inverters between grid-connected and stand-alone modes. The grid-connected inverter should operate in grid-tied and off-grid modes in order to provide power to the emergency load during system outages. However, the grid current controller and the output voltage controller are switched between the two modes, so the outputs of both controllers may not be equal during the transfer instant, which will cause the current or voltage spikes during the switching process. The transfer between the two controllers does not exist in the proposed method. In grid-tied mode, the voltage controller is used for compensating the filter capacitor current, and the current controller is used to control the grid current. In stand-alone mode, the voltage controller is used to regulate the output voltage, whereas the output of the current controller is zero. With the proposed control method, the seamless transfer can be achieved between both modes, even in polluted grid voltage. The principle and realization conditions of the control methods at both modes are analyzed. The detailed process of the seamless transfer between the two modes is illustrated. Finally, the simulation and experimental results verify the theoretical analysis.
38408
Reiter T et.al
PWM Dead Time Optimization Method for Automotive Multiphase DC/DC-Converters
IEEE Transactions on Power Electronics, Vol.25; No.6; May 2010; 1604 – 1614
This paper introduces a PWM dead time optimization method for multiphase DC/DC-converters with synchronous rectifiers. The aim of the method is to reduce power losses. After a perturbation of the dead times in one converter phase, the phase-currents starts to deviate, whereby the most efficient phase has the higher current. A current balancing controller compensates for this deviation by adjusting duty cycles. Consequently, optimal dead times can be detected by duty cycle differences of the phases. The proposed optimization approach was implemented in a two-phase boost-/buck converter prototype for automotive dual-voltage power-nets. No additional components or circuit modifications were necessary. The detection of optimal dead times, increasing efficiency and reduction of voltage transients are discussed and investigated experimentally.
38409
Li K.et.al
Dynamic Simulator for Thyristor-Controlled Series Capacitor
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 1096 – 1102
This paper presents an alternative approach to thyristor-controlled series capacitor (TCSC) performance analysis. The approach is to interface a small-scale physical model of the TCSC with a classic physical power system simulation laboratory. The platform is capable of investigating the operation, protection, and control strategies of TCSCs. Furthermore, it can be used to investigate complex phenomena such as the breakdown of metal oxide varistors. Such phenomena are very difficult, if not impossible, to investigate using digital simulation methods.
38410
Chang, J.S et.al
Narrow-Flow-Channel-Driven EHD Gas Pump for an Advanced Thermal Management of Microelectronics
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 1151 - 1158
In order to study the feasibility of applying electrohydrodynamic (EHD) gas pumps for advanced thermal management of microelectronics, an experimental investigation was conducted to drive gas flow through a narrow flow channel by an EHD gas pump. The net gas flow induced by corona discharge was generated by a push-fan (PF)-type EHD gas pump with and without a partially covered corona wire and nonparallel ground plate electrodes to transfer gas through millimeter-order circular channels. Therefore, it is important to know the effect of a narrow channel on the characteristics of the EHD gas pump with the corona wire electrode covered. The results show that the effects of narrow circular flow channels significantly influence the flow characteristics of the PF-type EHD gas pump and that the use of an insulator on the corona wire electrode can significantly enhance the current flux density and the pump performance under dc positive applied voltage.
38411
Lidong Zhang et.al
Power-Synchronization Control of Grid-Connected Voltage-Source Converters
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 809 – 820
In this paper, a novel control method of grid-connected voltage-source converters (VSCs) is proposed. The method can be generally applied for all grid-connected VSCs but may be of most importance in high-voltage dc (HVDC) applications. Different from the previous control methods, the proposed method utilizes the internal synchronization mechanism in ac systems, in principle, similar to the operation of a synchronous machine. By using this type of power-synchronization control, the VSC avoids the instability caused by a standard phase-locked loop in a weak AC-system connection. Moreover, a VSC terminal can give the weak ac system strong voltage support, just like a normal synchronous machine does. The control method is verified by both analytical models and time simulations.
38412
Majumder R
Power Management and Power Flow Control With Back-to-Back Converters in a Utility Connected Microgrid
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 821 – 834
This paper proposes a method for power flow control between utility and microgrid through back-to-back converters, which facilitates desired real and reactive power flow between utility and microgrid. In the proposed control strategy, the system can run in two different modes depending on the power requirement in the microgrid. In mode-1, specified amount of real and reactive power are shared between the utility and the microgrid through the back-to-back converters. Mode-2 is invoked when the power that can be supplied by the distributed generators (DGs) in the microgrid reaches its maximum limit. In such a case, the rest of the power demand of the microgrid has to be supplied by the utility. An arrangement between DGs in the microgrid is proposed to achieve load sharing in both grid connected and islanded modes. The back-to-back converters also provide total frequency isolation between the utility and the microgrid. It is shown that the voltage or frequency fluctuation in the utility side has no impact on voltage or power in microgrid side. Proper relay-breaker operation coordination is proposed during fault along with the blocking of the back-to-back converters for seamless resynchronization. Both impedance and motor type loads are considered to verify the system stability. The impact of dc side voltage fluctuation of the DGs and DG tripping on power sharing is also investigated. The efficacy of the proposed control arrangement has been validated through simulation for various operating conditions. The model of the microgrid power system is simulated in PSCAD.
38413
Rylander M et.al
Power Electronic Transient Load Model for Use in Stability Studies of Electric Power Grids
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 914 - 921
This paper develops a new large-signal transient load model to represent the composite power electronic load at a network bus. Traditional load models do not account for the transient responses of power electronic loads which occur at the onset and clearing of voltage sags. The new model is supported with actual utility fault response data and laboratory controlled tests. This paper shows that power electronic loads have a unique impact on generator rotor angle swings compared to those using conventional load models.
38414
Chaudhuri N.R. et.al
A New Approach to Continuous Latency Compensation With Adaptive Phasor Power Oscillation Damping Controller (POD)
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 939 – 946
Latency or delay in remote feedback signals can adversely affect the closed-loop damping performance. Accurate time-stamp information at both (PMU location and control center) ends offers a possibility to continuously compensate for time-varying latency. In this paper, an adaptive phasor power oscillation damping controller (APPOD) is proposed wherein the rotating coordinates for phasor extraction are adjusted to account for the change in phase caused due to the delay. The oscillatory component of the original signal is thus retrieved out of the delayed signal received at the control center. Unlike conventional phasor POD, which uses a fixed phase shift to generate damping control signal, an adaptive phase shift algorithm is used here to suit varying signal locations and operating conditions. Case studies confirm the effectiveness of the proposed technique, both in terms of robustness and handling continuously varying delays. A comparison with a conventional gain scheduled POD (CGPOD) and a Unified Smith Predictor (USP) approach is also presented.
5. POWER SYSTEM
38415
Khatod D.K. et.al
Analytical Approach for Well-Being Assessment of Small Autonomous Power Systems With Solar and Wind Energy Sources
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 535 – 545
This paper presents a systematic analytical approach for the well-being assessment of small autonomous power systems (SAPSs) with wind and solar energy sources. The proposed technique accounts for the uncertainties associated with solar irradiance, wind speed, demand, and outages of various generating units. The impact of wind power fluctuation on the system stability is also assessed by limiting the wind power dispatch to a certain percentage of system load. Well-being assessment and production costing simulation for SAPS are performed using proposed analytical approach and Monte Carlo simulation (MCS) method, and then, obtained results are compared in terms of accuracy and computational time. The comparison shows that the developed technique requires less computational time than MCS method, with reasonable accuracy, and thus, validates the usefulness of proposed analytical method. The impact of renewable energy penetration on a SAPS is also analyzed using the proposed method.
38416
Liangyu Ma et.al
An Intelligent Power Plant Fault Diagnostics for Varying Degree of Severity and Loading Conditions
IEEE Transactions on Energy Conversion, Vol.25; No.2; June 2010; 546 – 554
Practical fault diagnosis of a thermal system is very important in ensuring safe and reliable operation of a power plant. However, it is a difficult task due to the structural complexity of a thermal system, varying degree of severity of a fault, and the wide range of operation of the power generating unit. An artificial neural network combined with optimal zoom search is proposed in this paper for recognizing varying degrees of faults in a power plant thermal system operating at different load level. The zoom search technology is based on the similarity rules of the feature variables to a same fault with different severity when the system topological structure does not change with fault or with different loading conditions. Two different types of symptoms, a trend symptom and a semantic symptom, are calculated and jointly used for on-line fault recognition, which results in a faster and more stable fault diagnosis. A feedforward neural network structure is adopted and an improved training method is introduced. A high-pressure feedwater heater system is taken as a target system for investigation. Several simulation tests for diagnosing a multidegree fault under different operating conditions are carried out on a 300-MW power plant simulator to demonstrate the validity of the method.
38417
Wei-Shih Liu et.al
Analysis, Design, and Control of Bidirectional Cascoded Configuration for a Fuel Cell Hybrid Power System
IEEE Trans. on Power Electronics, Vol.25; No.6; May 2010; 1565 - 1575
This paper presents a cascoded configuration combining a fuel cell (FC), a battery, and an ultracapacitor module (UCM) to create a hybrid power system. A cascoded configuration is constructed using a modified bidirectional flyback converter, which connects the battery and UCM in cascode to efficiently provide hybrid power. An active FC voltage control strategy is presented to manage the power flows of the proposed cascoded system. In this paper, the simulated hybrid power of the motion of an electric vehicle is illustrated in different situations. The experimental results show that the power flows using the proposed control strategy verify the theoretical analysis. In addition, the overall efficiency of the proposed hybrid power system at overload operation is much higher than the conventional one, and it can achieve 96%.
38418
Chung I.Y
Control Methods of Inverter-Interfaced Distributed Generators in a Microgrid System
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 1078 – 1088
Microgrids are a new concept for future energy distribution systems that enable renewable energy integration and improved energy management capability. Microgrids consist of multiple distributed generators (DGs) that are usually integrated via power electronic inverters. In order to enhance power quality and power distribution reliability, microgrids need to operate in both grid-connected and island modes. Consequently, microgrids can suffer performance degradation as the operating conditions vary due to abrupt mode changes and variations in bus voltages and system frequency. This paper presents controller design and optimization methods to stably coordinate multiple inverter-interfaced DGs and to robustly control individual interface inverters against voltage and frequency disturbances. Droop-control concepts are used as system-level multiple DG coordination controllers, and L1 control theory is applied to device-level inverter controllers. Optimal control parameters are obtained by particle-swarm-optimization algorithms, and the control performance is verified via simulation studies.
38419
Mitolo M. et.al
Of International Terminology and Wiring Methods Used in the Matter of Bonding and Earthing of Low-Voltage Power Systems
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 1089 – 1095
The worldwide global market requires electrical engineers to have a deep understanding of the bonding and earthing practices adopted in different countries around the world. This knowledge is essential to obtain effective designs and high safety standards and can promote the elimination of technical obstacles that can still create market barriers. The full comprehension of the “grounding” theory requires the command of key technical concepts regarding the earthing methods, which may cause confusion when used in the North American technical realm rather than in the International Electrotechnical Commission (IEC) world. This issue is further worsened by the lack of literature in this matter, as well as of harmonization documents between national codes and international standards. This paper, by analyzing the protection against indirect contact in ac (50/60-Hz) low-voltage power systems by automatic disconnection of supply, seeks to clarify both the terminologies and each type of grounding system adopted in IEC standards, with the intent to create a common reference for practicing engineers in the matter of bonding and earthing of power systems. Major differences encountered between sizing procedures adopted in IEC standards and the North American National Electrical Code are also examined.
38420
Mitolo M
Effects of High Fault Currents on Ground Grid Design
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 1118 – 1124
Due to increased load demands and reduced incentives to build new transmission lines, energy companies are increasing power flows on the existing transmission assets, which will increase the fault current levels (for both three-phase and phase-to-ground faults) throughout the power system. New generation sources to be added at the transmission and distribution network will increase fault current intensities. It is crucial for the users of industrial facilities to be aware of increased ground-fault current magnitude at the service entrance and of the actual condition of the grid. The protection that ground grids provide against step and touch potentials is only good up to the expected level and duration of ground-fault currents, as originally communicated by the electric utility in the design phase. In addition, thermal and mechanical stresses to the customer's ground grid and ground grid connections can increase the grid's resistance to ground and, at the same time, fault potentials. In order to prevent these problems from occurring, a ground grid assessment, utilizing field and utility updated data, should be carried out on a regular basis. This paper will illustrate a European Committee for Electrotechnical Standardization (CENELEC) approach to ground grid design, aimed to maximize the electrical safety under ground fault. In addition, case studies will be included, showing how high fault currents have damaged ground grids and what repairs are possible.
38421
Malpani R. et.al
High Precision Frequency Estimation Using Internet-Based Phasor Measurement Unit
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 607 - 614
This paper presents a measurement technique suited for real-time transfer, monitoring and processing of state variables in power distribution networks, in terms of synchronized phasors. The proposed technique, different from commercial phasor measurement units (PMUs), is based on general purpose data acquisition hardware and uses network time protocol (NTP) for accurate time-stamping of the measurements. A least square approximation scheme for accurate frequency estimation is proposed, and with this scheme, it has been proved that the range of frequency with zero estimation error increases with the increase in number of re-samplings.
38422
Yixin Cai et.al
Statistical Feature Selection From Massive Data in Distribution Fault Diagnosis
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 642 – 648
Selecting proper features to identify the root cause is a critical step in distribution fault diagnosis. Power engineers usually select features based on experience. However, engineers cannot be familiar with every local system, especially in fast growing regions. With the advancing information technologies and more powerful sensors, utilities can collect much more data on their systems than before. The phenomenon will be even more substantial for the anticipating Smart Grid environments. To help power engineers select features based on the massive data collected, this paper reviews two popular feature selection methods: 1) hypothesis test, 2) stepwise regression, and introduces another two: 3) stepwise selection by Akaike's Information Criterion, and 4) LASSO/ALASSO. These four methods are compared in terms of their model requirements, data assumptions, and computational cost. With real-world datasets from Progress Energy Carolinas, this paper also evaluates these methods and compares fault diagnosis performance by accuracy, probability of detection and false alarm ratio. This paper discusses the advantages and limitations of each method for distribution fault diagnosis as well.
38423
Veliz F.F.C et.al
A Comparison of Load Models for Composite Reliability Evaluation by Nonsequential Monte Carlo Simulation
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 649 – 656
This paper presents a comparison of Markov load models for composite reliability evaluation by nonsequential Monte Carlo simulation. The proposed models represent the whole system load curve. The first model (M1) is an aggregated Markov model that represents all different states present in the load curve, without using any clustering technique. The second model (M2) consists of a hybrid Markov model, where all different levels of the load curve are also represented but it tries to preserve some chronology of the load curve. The third model (M3) consists of a non-aggregated Markov model. The frequency and duration (F&D) indices are calculated by the conditional probability method for all models. The indices calculated using these models are compared with the indices obtained when the usual clustered aggregated Markov model (M0) is used. The indices obtained by sequential Monte Carlo simulation with a chronological system load curve are used as comparison reference in order to validate the presented models.
38424
Yi-Shan Zhang & Hsiao-Dong Chiang
Fast Newton-FGMRES Solver for Large-Scale Power Flow Study
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 769 - 776
A fast Newton-FGMRES method for power flow calculations is proposed in this paper. Three accelerating schemes to speed up the Newton-FGMRES method are proposed. Numerical studies show that the proposed fast Newton-FGMRES method consistently outperforms the traditional Newton-GMRES method and Newton-LU method on two practical power systems-one with 12 000 buses, another with 21 000 buses. For the 21 000-bus system, the fast Newton-FGMRES method can be 45.7% faster than the traditional Newton-LU method.
38425
Tao Xia & Yilu Liu
Single-Phase Phase Angle Measurements in Electric Power Systems
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 844 – 852
Computation of phase angles using the discrete Fourier transform (DFT) algorithm has been proven to be sufficiently accurate in a variety of power system applications when the input signal is three-phase voltage and the voltage frequency is near the nominal value. However, the performance of the DFT algorithm in time of the singe-phase voltage input with a large frequency excursion so far has not been well explored, much less documented. This paper briefly discusses the importance of the synchronized phase angle measurement in power systems, and brings up the necessity of research on single-phase measurement systems. The performance of the DFT algorithm in power system phase angle measurements is thoroughly analyzed. Corresponding rectifying methods, including quasi-positive-sequence DFT and offset compensation, are proposed and examined by relevant numerical simulations and necessary laboratory tests. The results of the simulations and tests show a perfect match between the derived equations and the phase angle data, and thus verify the effectiveness of the proposed algorithm, which is believed to be able to greatly improve the performance of DFT in the aspect of phase angle calculation when severe power system upsets with remarkable frequency excursions are present.
38426
Karimi H. et.al
Multivariable Servomechanism Controller for Autonomous Operation of a Distributed Generation Unit: Design and Performance Evaluation
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 853 - 865
A linear time-invariant (LTI) robust servomechanism controller for islanded (autonomous) operation of a distributed generation (DG) unit and its local load is proposed. The DG unit utilizes a voltage-sourced converter (VSC) as the interface medium. The controller design is obtained by introducing a new optimal controller design procedure, in conjunction with a proposed non-conservative robustness constraint. The proposed controller utilizes 1) an internal oscillator for frequency control and 2) a robust servomechanism controller (RSC) to regulate the island voltage. Despite uncertainty of the load parameters, the proposed controller guarantees robust stability and pre-specified performance criteria, e.g., fast transient response and zero steady-state error. The theoretical aspects of the proposed robust servomechanism controller including the existence conditions, design of the controller, and robust stability analysis of the closed-loop system are studied. Moreover, the performance of the robust servomechanism controller based on 1) simulation studies in the MATLAB software environment, and 2) experiments in a laboratory-scale setup, is presented in this paper. In particular, reference signal tracking and robustness of the closed-loop system with respect to the load parameter uncertainty are investigated. Both computer simulation studies and experimental results confirm that the proposed robust controller provides the specified performance characteristics of the closed-loop system.
38427
Kshatriya N.et.al
Optimized Partial Eigenstructure Assignment-Based Design of a Combined PSS and Active Damping Controller for a DFIG
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 866 – 876
The paper applies the method of eigenstructure assignment for the design of a controller for a wind generation scenario in Northern Scotland based on doubly-fed induction generators (DFIGs). The designed controller serves the combined purpose of a conventional power system stabilizer (PSS) and an active damping controller and provides a contribution to both network and shaft damping. This novel approach is superior because all available degrees of freedom are fully exploited by selecting not only the new eigenvalue locations but also certain elements of the left eigenvectors. These elements are obtained by solving a multiobjective nonlinear optimization problem (MONLOP). Examples are presented to demonstrate that optimizing the eigenvectors yields a better performing controller in comparison with one designed using mere eigenvalue relocation.
38428
Rommes J et.al
Computing Rightmost Eigenvalues for Small-Signal Stability Assessment of Large-Scale Power Systems
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 929 – 938
Knowledge of the rightmost eigenvalues of system matrices is essential in power system small-signal stability analysis. Accurate and efficient computation of the rightmost eigenvalues, however, is a challenge, especially for large-scale descriptor systems. In this paper we present an algorithm, based on subspace accelerated Rayleigh quotient iteration (SARQI), for the automatic computation of the rightmost eigenvalues of large-scale (descriptor) system matrices. The effectiveness and robustness of the algorithm is illustrated by numerical experiments with realistic power system models, and we also show how SARQI can be used to compute eigenvalues closest to any damping ratio and repeated eigenvalues. The algorithm can be used for stability analysis in any other field of engineering.
38429
Gomez F
Rotor Angle Instability Prediction Using Post-Disturbance Voltage Trajectories
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 947 – 956
A new method for predicting the rotor angle stability status of a power system immediately after a large disturbance is presented. The proposed two-stage method involves estimation of the similarity of post-fault voltage trajectories of the generator buses after the disturbance to some pre-identified templates and then prediction of the stability status using a classifier which takes the similarity values calculated at the different generator buses as inputs. The typical bus voltage variation patterns after a disturbance for both stable and unstable situations are identified from a database of simulations using fuzzy C-means clustering algorithm. The same database is used to train a support vector machine classifier which takes proximity of the actual voltage variations to the identified templates as features. Development of the system and its performance were demonstrated using a case study carried out on the IEEE 39-bus system. Investigations showed that the proposed method can accurately predict the stability status six cycles after the clearance of a fault. Further, the robustness of the proposed method was examined by analyzing its performance in predicting the instability when the network configuration is altered.
38430
Ruisheng Diao et.al
Design of a Real-Time Security Assessment Tool for Situational Awareness Enhancement in Modern Power Systems
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 957 - 965
Detailed security analysis for N-k contingencies (k = 1, 2, 3, ...) in a real-time setting is still a great challenge due to the significant computational burden. This paper takes advantage of phasor measurement units (PMUs) and decision trees (DTs) to develop a real-time security assessment tool to assess four important post-contingency security issues, including voltage magnitude violation (VMV), thermal limit violation (TV), voltage stability (VS) and transient stability (TS). The proposed scheme is tested on the Salt River Project (SRP) power system represented by a series of operating conditions (OCs) during a representative day. The properly trained DTs demonstrate excellent prediction performance. Robustness tests for the offline trained DTs are performed on a group of changed OCs that were not included for training the DTs and the idea of tuning critical system attributes for preventive controls is also presented to improve system security.
38431
Gurrala G. & Sen I.
Power System Stabilizers Design for Interconnected Power Systems
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 1042 – 1051
This paper proposes a method of designing fixed parameter decentralized power system stabilizers (PSS) for interconnected multi-machine power systems. Conventional design technique using a single machine infinite bus approximation involves the frequency response estimation called the GEP(s) between the AVR input and the resultant electrical torque. This requires the knowledge of equivalent external reactance and infinite bus voltage or their estimated values at each machine. Other design techniques using P-Vr characteristics or residues are based on complete system information. In the proposed method, information available at the high voltage bus of the step-up transformer is used to set up a modified Heffron-Phillip's model. With this model it is possible to decide the structure of the PSS compensator and tune its parameters at each machine in the multi-machine environment, using only those signals that are available at the generating station. The efficacy of the proposed design technique has been evaluated on three of the most widely used test systems. The simulation results have shown that the performance of the proposed stabilizer is comparable to that which could be obtained by conventional design but without the need for the estimation and computation of external system parameters.
38432
Troy N et.al
Base-Load Cycling on a System With Significant Wind Penetration
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 1088 – 1097
Certain developments in the electricity sector may result in suboptimal operation of base-load generating units in countries worldwide. Despite the fact they were not designed to operate in a flexible manner, increasing penetration of variable power sources coupled with the deregulation of the electricity sector could lead to these base-load units being shut down or operated at part-load levels more often. This cycling operation would have onerous effects on the components of these units and potentially lead to increased outages and significant costs. This paper shows the serious impact increasing levels of wind power will have on the operation of base-load units. Those base-load units which are not large contributors of primary reserve to the system and have relatively shorter start-up times were found to be the most impacted as wind penetration increases. A sensitivity analysis shows the presence of storage or interconnection on a power system actually exacerbates base-load cycling until very high levels of wind power are reached. Finally, it is shown that if the total cycling costs of the individual base-load units are taken into consideration in the scheduling model, subsequent cycling operation can be reduced.
38433
Shyh-Jier Huang & Hsing-Ho Wan
A Method to Enhance Ground-Fault Computation
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 1190 – 1191
This letter presents a simple criterion for reviewing balanced three-phase fault and unbalanced ground-fault current using the ratio of zero sequence impedance to positive sequence impedance as seen from the fault location, which can be employed to enhance the power system design and protection. The method has been verified by real power systems in Taiwan with satisfactory results.
6. POWER TRANSMISSION & DISTRIBUTION
38434
Dilek M et.al
A Robust Multiphase Power Flow for General Distribution Networks
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 760 – 768
This paper presents a sweep-based three-phase power flow method for solving general distribution networks that can be heavily meshed and include transformers around the meshes/loops. A load-stepping technique is proposed for solving common convergence problems of sweep-based load-flow solvers when dealing with overloaded radial sections. The proposed power-flow algorithm is based on the iterative solution of radial subsystems assembled together with the mesh equations to comply with Kirchhoff equations. The proposed method is robust and efficient for the solution of heavily loaded systems. Examples are presented for illustration.
38435
Chun-Lien Su
Stochastic Evaluation of Voltages in Distribution Networks With Distributed Generation Using Detailed Distribution Operation Models
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 786 – 795
Distributed generation (DG) connected to distribution networks affects the currents or power flows in the networks; thus, node voltages that are strongly related to power flows also are changed. As the voltage must be within permitted limits to comply with utility and customer requirements, this effect should be assessed prior to DG connection. At the distribution level there are a number of attributes that can influence the voltage profiles; therefore, this assessment requires detailed distribution operation models. To provide reliable voltage evaluation results, a new probabilistic methodology is proposed in this paper. The distribution system operation uncertainties including daily time varying load, stochastic DG power production, network configuration, and voltage control devices operation are all taken into account. A probabilistic load flow method based on an efficient algorithm is used to handle uncertainties in loads and DG output power and voltage control devices operation. Accordingly, a probabilistic network reconfiguration model is employed to take stochastic network configurations for service restoration or load balancing into consideration. The proposed probabilistic method provides a better knowledge of the voltage effects and can be used for evaluating the level of DG that might be accepted on a distribution network. The models developed can also be used for assessing impact of voltage mitigation equipment on distribution operating performance. Test results of a modified IEEE feeder test system demonstrate the performance of the proposed method.
7. PROTECTION & PROTECTIVE DEVICES
38436
Chun-Yu Hsieh
A Low-Dropout Regulator With Smooth Peak Current Control Topology for Overcurrent Protection
IEEE Transactions on Power Electronics, Vol.25; No.6; May 2010; 1386 – 1394
The proposed low-dropout (LDO) regulator with a smooth peak current control (SPCC) circuit can be simultaneously controlled by using an error amplifier to regulate output voltage and a peak current controller as a means to limit its current level. The SPCC circuit can be switched smoothly between these two control mechanisms by detecting the information of load current and the dropout voltage. Measured results show that overcurrent protection can make the pass device operate as a current source while the load current exceed the peak current level. Moreover, the control mechanism can return to error amplifier control when load current becomes smaller than the limiting current, thus ensuring output voltage to be close to the rated value. Output voltage is stable and varies smaller than 15 mV when a 160 mA load current step or a 2 V supply voltage step is placed on this LDO regulator.
38437
Licheng Jin
Model Predictive Control-Based Real-Time Power System Protection Schemes
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 988 – 998
The objective of power system controls is to keep the electrical flow as well as voltage magnitudes within acceptable limits in spite of the load and network topology changes. The control of voltage level is accomplished by controlling the production, absorption as well as flow of reactive power at various locations in the system. This paper presents an approach to determine a real-time system protection scheme to prevent voltage instability and maintain a desired amount of post-transient voltage stability margin (an index of system security) following the occurrence of a contingency by means of reactive power control. This approach is based on the model predictive control (MPC) theory. According to an economic criterion and control effectiveness, a control switching strategy consisting of a sequence of amounts of the shunt capacitors to switch is identified for voltage restoration. The effect of the capacitive control on voltage recovery is measured via trajectory sensitivity. The sensitivity of voltage stability margin with respect to the capacitive control is used to construct a security constraint for post-fault operation in the MPC formulation. The efficacy of the proposed approach is illustrated through applications to the WECC system for enhancing the voltage performance and to the 39-bus New England system for preventing voltage collapse.
8. TESTING
38438
Sugimoto T et.al
Corona Charging and Current Measurement Using Phi-Type Corona Electrodes
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 1175 – 1180
In order to develop a noncontact surface resistivity measurement technique, the corona charging of a test material with simultaneous measurement of an induction current caused by a traveling surface charge was investigated using phi-type electrodes. The phi-type electrode consists of a high-voltage needle electrode that penetrates a circular hole of a grounded planar electrode. The phi-type electrode is positioned above an electrically isolated test material. The purpose of the electrode design is to supply static charge to the test surface, to produce a ground potential close to the charged test material, and then to measure the induction current or the surface potential caused by the propagated surface charge. Test materials with surface resistivities from 106 to 1012 Ω/0 were prepared by coating conductive polymer layers onto polyvinyl chloride disks. Two setups were prepared for higher surface resistivity (Model H) and lower surface resistivity (Model L). For Model H, a surface voltmeter was used to measure the slow propagation of surface charge. The rise time of the surface potential increased linearly with the surface resistivity from 3 x 109 to 1 x 1012 Ω/0 . The Model L had two induction probes to measure the fast propagation of surface charge. The rate of the total induction charges was a function of the surface resistivity from 3 x 106 to 3 x 109 Ω/0. Experimental results obtained from both the H and L models agreed with the predicted results. The phi-type electrode was veri- - fied as effective for noncontact surface charge measurements.
38439
Hodgson, D. L. & Shipp D.
Arc-Flash Incident Energy Reduction Using Zone Selective Interlocking
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 1243 – 1251
As a result of new requirements in the National Fire Protection Association (NFPA) 70E standard, many facilities are performing arc-flash hazard analyses to better understand how to protect personnel from the possibility of being injured in an arc-flash incident. In many cases in the petrochemical industry, it is unsafe or not practical to shut down electrical equipment to do work. This paper explores practicable options that a facility has to reduce incident energy levels in existing low-voltage systems where the arc-flash hazard analysis results in unacceptably high levels. It also explores a case study in the Gulf of Mexico, where an offshore oil production platform was able to cost effectively reduce incident energy levels from approximately 170 to under 15 calories / cm2 by implementing a zone selective interlocking system into their low-voltage switchgear. The selection process logic involving equipment, personnel considerations, and commissioning are all addressed.
9. TRANSFORMERS
38440
Margueron X. et.al
Current Sharing Between Parallel Turns of a Planar Transformer: Prediction and Improvement Using a Circuit Simulation Software
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 1064 – 1071
As a consequence of the increase of power needs in low-voltage applications, wiring several windings in parallel to sustain large currents has become common. This choice may have a serious impact on the transformer reliability. In practice, due to additional currents that we call “circulation currents,” highly localized extra losses occur. Although hot points resulting from these currents can destroy the component, the related losses are generally not taken into account by analytical approaches. In planar transformers, windings are made of printed circuit board layers, and circulation currents lead to severe unbalance of current sharing between parallel layers. This paper presents an analytical method enabling the evaluation of the currents in every layer using only a circuit simulation software such as Pspice or PSIM. For a designer, this method is very intuitive and fast compared with the use of finite element method simulations. Several extensions of the modeling method used here are also presented.
38441
Ku T.T. & Lin C.H.
Design of PLC-Based Identifier to Support Transformer Load Management in Taipower
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 1072 – 1077
To support transformer load management, a narrow-band power line carrier (PLC)-based identifier has been designed and developed for the determination of customers served by each distribution transformer. The transmission characteristics of a PLC signal over low-voltage distribution lines is simulated by using the mathematical model of distribution transformers, line conductors, and customer loading at high frequencies of the carrier signal. After completing the development of PLC-based identifier, a field test has been executed to verify the performance of the identifier to determine the connectivity of the distribution transformer and the customers served without requiring power service interruption. With the customer account numbers updated by the PLC identifier, the monthly energy consumption and the service type of customers served by each distribution transformer are retrieved from the customer information system. The daily power profile and peak loading of the distribution transformers are then derived according to the energy consumption and the typical load patterns of the customers served.
38442
Saleh S. A.& Rahman M. A.
Testing of a Wavelet-Packet-Transform-Based Differential Protection for Resistance-Grounded Three-Phase Transformers
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 1109 - 1117
This paper presents an extension of real-time tests of a wavelet-packet-transform-based technique for the differential protection of three-phase power transformers. The proposed technique is implemented using a DS1102 digital signal processor board and tested on two different three-phase power transformers with neutral resistance grounded. Different magnetizing inrush and internal fault currents are investigated with current transformer (CT) saturation for different loading conditions, including capacitive loads. The results show a complete independence from transformer parameters, load types, grounding method, or CT saturation. Furthermore, the proposed technique has high speed, good accuracy, small required memory, and reliable responses with reduced computational burden. In all cases of the investigated internal faults, the proposed algorithm is capable of identifying the fault and generating a trip signal in less than a quarter cycle based on a 60-Hz system.
10. OTHERS
38443
Shimizu K
Emission Spectroscopy of Pulsed Power Microplasma for Atmospheric Pollution Control
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 1125 - 1131
Pollution of the atmosphere from various sources, including factories and automobiles, is a serious problem worldwide and should be controlled and reduced. Nonthermal plasma is studied by various groups and has been applied for exhaust gas treatment and indoor air purification. Microplasma, which is atmospheric pressure nothermal plasma, has recently been studied by many researchers. Although nonthermal-plasma diagnosis by emission spectroscopy has been applied by many authors, the mechanisms are not sufficiently understood. In this paper, the diagnosis of the microplasma discharge in N2 gas and N2/No mixture are presented. An experimental Marx generator with MOSFET switches was used to generate pulsed output voltages of up to 1.8 kV. Emission spectra were observed by a spectrometer with intensified charge-coupled device camera and a photomultiplier tube. The formation of radicals was confirmed by NO γ band, N2 x second positive band, and N2 first negative system. Time evolution of light emission that is measured by the photomultiplier tube showed differences between the NO γ band and the N2 second positive band. This condition is suggested to be the result of different light emission mechanisms; the N2 second positive band is excited by direct electron impact, and the NO γ formula formulatype="inline" γ band is excited by collisions of N2 metastables.
38444
Yu D. et.al
Dynamic Induction Charging of Particles With Finite Conductivity
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 1159 - 1165
Despite the common belief that, in the process of induction charging, the actual charging time constant and the material-based relaxation time constant are equal, there is no proof that these parameters are related at all. The purpose of this paper is to determine the actual induction charging time constant for practical types of particles having both finite conductivity and permittivity. All investigations were based on numerical simulations done for idealized geometric models of the problem. The model was developed for the transient case and solved by using the COMSOL commercial software, which is based on the finite-element method. Spherical and rough particles with various contact areas with the ground electrode were considered. The surface conduction of the particle was neglected. The effect of the particle contact area, conductivity, and permittivity on the actual charging time constant was investigated, and the results were compared with that predicted by the classic relaxation time constant, as defined by the material properties. It was found that the actual time constant is not equal to the relaxation time constant but is directly affected by the value of the contact area between the particle and ground electrode.
38445
Yoshioka Y et.al
Automatic Control Method of NO Removal by a Combination of Ozone Injection and Exhaust Gas Recirculation
IEEE Transactions on Industry Applications, Vol.46; No.3; May-June 2010; 1166 – 1174
NOx from diesel exhaust gases can efficiently be removed by a combination of ozone injection and exhaust gas recirculation (EGR). To industrialize the system, it is necessary to develop a NO control system because the NO concentration largely changes by an engine output power. In this paper, we constructed a NO control system without using any NOx sensor. As for the control method, we adopted two control methods: 1) an ozone control under a predetermined rate of the EGR and 2) an energy minimum control. The details of the automatic control methods are introduced in this paper. NO control experiments were carried out using a 2.4-kVA diesel engine generator, and the NO emissions were succes sfully controlled by the system.
38446
Chattopadhyay D.
Modeling Greenhouse Gas Reduction From the Australian Electricity Sector
IEEE Transactions on Power Systems, Vol.25; No.2; May 2010; 729 – 740
The Australian electricity sector is expected to undergo major changes to reduce the current sectoral CO2 emission of 190 million tons to 96 million tons by 2050. This paper summarizes two major modeling studies that have been undertaken since 2006 to understand the full set of investment, price and financial impact on existing generators, especially coal-based generators. We have used a long-term capacity and dispatch optimization model to comprehensively analyze both least-cost and market-led expansion of the system to accommodate alternative emission reduction targets from a shallow cut to a deep cut. The modeling results demonstrate the cost of meeting the target can be over $30 billion in NPV terms. A mix of clean coal technologies, gas and nuclear technologies is expected to displace the existing stock of conventional coal which varies significantly depending on the emission reduction target. The analysis also show that mandatory renewable targets or technology standards are inefficient policies in comparison to a market-based policy such as the proposed emissions trading scheme.
38447
Hyndman R.J. & Shu Fan
Density Forecasting for Long-Term Peak Electricity Demand
IEEE Transactions on