37014

Yang  X.  et.al 

Fault Location for Underground Power Cable Using Distributed Parameter Approach 

IEEE Transactions on Power Systems, Vo. 23; No. 4;  Nov. 2008; 1809-1816 

This paper proposes an extensive fault location model for underground power cable in distribution system using voltage and current measurements at the sending-end. First, an equivalent circuit that models a faulted underground cable system is analyzed using distributed parameter approach. Then, the analysis of sequence networks in three-phase network is obtained by applying the boundary conditions. This analysis is used to calculate a fault distance in single section using voltage and current equations. The extension to multi-section is further analyzed based on Korean distribution systems. This method is an iterative process to determine a faulted section from the network. Finally, the case studies are evaluated with variations of fault distance and resistance, which also includes the evaluation of its robustness to load uncertainty. 

37015

Van Schaik N.  et.al 

Conditions of Discharge-Free Operation of XLPE Insulated Power Cable Systems 

IEEE Transactions on Dielectrics and Electrical Insulation, Vol.15; No.4; August 2008; 1120-1130 

A coherent methodology was developed for analysing the risk of partial discharge inception in the insulation of high voltage cables containing spherical voids located at the conductor screen interface and fissures located at the insulation screen interface. These two types of insulation defects present the two most important cases from the point of view of insulation integrity in high voltage cable systems. Our approach was based on the notion of sensitivity of dielectric stress to dimensional change of cable insulation and the notion of sensitivity of the size of discharge free defect to the change of electric field intensity. We investigated how modifications of insulation dimensions can affect the risk of discharge in typical defects. The obtained results revealed that so called slim design of HV cables requires that the size of voids is reduced by approximately a third to ensure discharge free operation. The size of fissures must be reduced approximately tenfold in comparison to the permissible size of similar fissures in a standard design to ensure discharge free operation at the interface with accessories. This poses a very high technological demand on new cable system designs of this type. Increasing the size of cable core creates an increased risk of partial discharge, mainly in fissures. Based on the dimensions of a typical 110 kV cable we showed that a reduction of fissure dimensions by approximately a quarter is required for a discharge free operation if the conductor size increases from 1000 mm2 to 2000 mm2. We have quantified this way the extent to which quality of the insulation extrusion process as well as precision of accessories assembly must improve, in order to assure discharge free operation of cable systems after typical design modifications.

37016

Thomas A et.al

A New Dielectric Response Model for Water Tree Degraded XLPE Insulation ¿ Part B: Dielectric Response Interpretation

IEEE Transactions on Dielectrics and Electrical Insulation, Vol.15; No.4; August 2008; 1144-1152 

Dielectric response measurements, in both time and frequency domains, can generate valuable information about the condition of cables affected by water tree degradation. However, the interpretation of how these dielectric response measurements relate to water tree density and length is a difficult task. This difficulty in assessing in particular the longest water tree length from dielectric response measurements is a substantial limitation, as it is well known that the remaining electrical strength of a water tree degraded cable is related to the longest tree length. This paper will detail a study whose goal was to enhance the understanding of how water tree degradation (in particular long vented trees) influences the dielectric response, and therefore seeks to reduce this interpretation limitation. The paper examines the application of a finite element model for water tree degraded insulation. This application involves using the dynamic electrical behavior as predicted by the model to generate frequency domain dielectric responses. The predicted electrical behaviour of both bow-tie and vented trees and the dielectric response that such trees will produce is examined and compared to actual Frequency Domain Spectroscopy (FDS) measurements on water tree degraded cable samples. It is shown that the developed model can accurately reproduce such measurement behavior, including the non-linear response. Because of the success of the model in reproducing actual dielectric response measurements of water tree degraded cables, it has proven itself to be a useful interpretive tool for water tree detection and assessment. 

37017

Thomas, A.J.  & Saha T.K.   

A New Dielectric Response Model for Water Tree Degraded XLPE Insulation ¿ Part A: Model Development with Small Sample Verification 

IEEE Transactions on Dielectrics and Electrical Insulation, Vol.15; No.4; August 2008; 1131-1143 

Water tree degradation in underground XLPE insulated cables is a growing, worldwide problem. This form of degradation is ultimately fatal for affected cables, and therefore the detection of damaging trees in power cable insulation is vital for distribution companies to avoid catastrophic failure. Dielectric response measurements, in both the time and frequency domains, can generate valuable information about the condition of the cable. However, the interpretation of how these dielectric response measurements relate to water tree density and length is a difficult task. This paper will present a new dielectric response model for water tree degraded XLPE insulation. The model is based on finite element analysis to determine the electrical behaviour of water tree degraded insulation. Preliminary simulations will verify the model development by comparing the results to small sample pulsed electro-acoustic (PEA) measurements performed by other researchers. The importance of a strong non-linearity mechanism for accurate modelling will also be elucidated. 

37018

Tozzi, M.  et.al 

PD Detection Limits in Extruded Power Cables Through Wide and Ultra-Wide Bandwidth Detectors 

IEEE Transactions on Dielectrics and Electrical Insulation, Vol.15; No.4; August 2008; 1183-1189 

The aim of this paper is to infer partial discharge (PD) detection limits in extruded cables as a function of the distance between PD source and detection point. The investigation is carried out for different types of detectors, from IEC 60270-compliant to ultra-wide bandwidth systems. For this purpose, a medium voltage cable has been modeled as a transmission line with frequency-dependent parameters accounting for skin effect, dielectric and semicon characteristics. Pulse propagation through the cable has been predicted for very long distances. Different filters have been used to simulate different detectors, emphasizing the behavior of these systems, particularly the features of sensitivity, noise rejection, PD source separation and PD source localization. 

37019

Wagenaars, P.

Accurate Estimation of the Time-of-Arrival of Partial Discharge Pulses in Cable Systems in Service

IEEE Transactions on Dielectrics and Electrical Insulation, Vol.15; No.4; August 2008; 1190-1199

Accurate location of the origins of partial discharges in power cable systems, based on arrival times, is imperative for the identification and assessment of defects. This paper evaluates different time-of-arrival algorithms in order to determine which method yields most accurate location under different circumstances. These methods are based on trigger level, Akaike Information Criterion, energy criterion, Gabor's signal centroid and phase in frequency domain. Several criteria are defined by which the algorithms are evaluated. These criteria include the sensitivity to noise, pulse shape and effect of load impedance. The sensitivity of the methods upon varying these quantities is evaluated analytically and by means of simulations. Further, the methods are tested on a medium-voltage cable system by injecting PD pulses in a cable with one joint. Each algorithm is applied to the measured pulses and the resulting location is compared with the known joint location. From the results the energy criterion method and the phase method show the best performance. 

37020

Jim Jun Guo   

High Frequency Attenuation in Transmission Class Solid Dielectric Cable 

IEEE Transactions on Power Delivery, Vol.23; No.4; Oct. 2008; 1713-1719 

High frequency attenuation in shielded distribution cable is well understood; however, this cannot be said of transmission class solid dielectric cable, which has a more complicated structure, including additional semiconducting ldquobeddingrdquo layers and a moisture barrier in the form of metal tape or corrugated metallic sheath. These additional elements cause new sources of high frequency loss relative to solid dielectric distribution cable. We report measurements of high frequency loss for transmission class solid dielectric cable with a corrugated copper sheath and for cable with a metal tape moisture barrier and wire screen (concentric neutral). Analytic approximations have been developed for the various sources of high frequency loss in these cable structures, and the analytic approximations have been checked using finite element analysis. Good agreement has been achieved between the computed and measured loss. 

37021

Cataliotti A.  et.al 

Power Line Communication in Medium Voltage Systems: Characterization of MV Cables 

IEEE Transactions on Power Delivery, Vol.23; No.4; Oct. 2008; 1896-1902 

The aim of this paper is to illustrate the development of a theoretical and experimental study on the characterization of medium voltage (MV) cables in the frequency range 25-200 kHz. Two transmission line configurations, line-ground and line-line, were considered in order to evaluate the main parameters, such as the characteristic impedance and the attenuation constant alpha. A simplified model of the line-ground configuration is proposed which allows one to evaluate the characteristic impedance and the attenuation constant by means of geometrical dimensions. The model was verified by experimental measurements on commonly used MV cables, RG7H1R, with an aluminium core of different sections, 95 mm² and 185 mm². Moreover, the experimental tests were carried out for the line-line configuration.

 

37022

Popovic L.M.   

Influence of Metal Installations Surrounding the Feeding Cable Line on the Ground Fault Current Distribution in Supplied Substations 

IEEE Transactions on Power Delivery, Vol.23; No.4; Oct. 2008; 2583-2590 

This paper presents the method for taking into consideration the influence of metallic installations surrounding the feeding line on the ground fault current distribution in supplied substations. When a ground fault occurs in a substation supplied by a cable line, these installations can significantly participate in reducing the part of the ground fault current emanating through the grounding system of this substation into the surrounding earth. Since only this part of the ground fault current creates potentials on the grounding system, this also means the reduction of all potential differences (touch and step voltages) appearing during the ground fault inside and in the vicinity of the supplied substation. However, current analytical expressions for the determination of the cable line reduction factor do not take into consideration this favorable effect. It is also not possible to determine it by direct measurements. This paper presents a method which enables us to achieve this by using the results of reduction factor measurements and by modeling surrounding metallic installations as a single equivalent conductor, cylindrical in form and parallel with the cable line. 

37023

Tripathi P. C. 

Cables / Cabling Systems in Large Thermal Power Plants 

Electrical India, Vol. 48, NO. 9, Sept 2008; 64-66 p 

This article deals with this current trends in cables / cabling system for electrical system of large thermal power plant.  Segment technical parameters of flame retardant low smoke (FRLS) cable and free survival (ES) C able are presented.  Types of Fire Sealing system and the latest trends in cabling are also included.  The performance  of electrical cables in fire situations is becoming more important considering the loss incurred due to fires in large thermal power stations.  Investigations and studies done by various consultants and users, reveal that fire rarely starts from cables due to internal overheating – as adequate design margins are provided.  But it is the cable insulation and sheath that help in propagating the fire particularly at places where cable densit7y is high.

37024

Prasad G. L. 

Development of New Range of special Alloy Conductors. 

Electrical India, Vol. 48, No. 10, October 2008, P. 70-72,74,76 

A new Aluminum alloy conductor having higher conductivity has been developed.  BY using these special alloy conductors, electric utility can achieve significant saving in both transmission and distribution lines.  A Sterlite Technologies AL-59 alloy conductor which has won the Best Product Award from IEEMA has found extensive use in electricity globally. 

37025

Dutta S.   & Singh S. P.  

Optimal Rescheduling of Generators for Congestion Management Based on Particle Swarm Optimization 

IEEE Transactions on Power Systems, Vo. 23; No. 4;  Nov. 2008; 1560-1569 

Power system congestion is a major problem that the system operator (SO) would face in the post-deregulated era. Therefore, investigation of techniques for congestion-free wheeling of power is of paramount interest. One of the most practiced and an obvious technique of congestion management is rescheduling the power outputs of generators in the system. However, all generators in the system need not take part in congestion management. Development of sound formulation and appropriate solution technique for this problem is aimed in this paper. Contributions made in the present paper are twofold. Firstly a technique for optimum selection of participating generators has been introduced using generator sensitivities to the power flow on congested lines. Secondly this paper proposes an algorithm based on particle swarm optimization (PSO) which minimizes the deviations of rescheduled values of generator power outputs from scheduled levels. The PSO algorithm, reported in this paper, handles the binding constraints by a technique different from the traditional penalty function method. The effectiveness of the proposed methodology has been analyzed on IEEE 30-bus and 118-bus systems and the 39-bus New England system.

37026

Martinez-Tarifa J.M.  et.al 

Frequency-Domain Model for Calculation of Voltage Distribution Through Random Wound Coils and Its Interaction With Stray Capacitances 

IEEE Transactions on Energy Conversion, Vo. 23; No. 3;  Sept. 2008; 742-751 

Modern pulsewidth-modulation (PWM) low-voltage drives are recognized as one of the most demanding applications for a motor. Pulses facing motor terminals are responsible for turn-to-turn high electrical stresses that lead to unexpected failures in stator windings. In this paper, an accurate new model for frequency-domain voltage distribution calculation through random wound coils is presented. In addition to checking its applicability for varnished coils, the role of stray capacitances in turn-by-turn voltage propagation is analyzed as well. Model accuracy is proved using experimental data in an experimental test cell. Finally, the same model is applied successfully to real random wound coils inserted in a motor stator core, and the ability to change turn-to-turn electrical stresses by means of changes in stray capacitances values will be quantified. 

37027

Fuchs E.F.  et.al 

Analysis of Critical-Speed Increase of Induction Machines via Winding Reconfiguration With Solid-State Switches 

IEEE Transactions on Energy Conversion, Vo. 23; No. 3;  Sept. 2008; 774-780 

Commonly used speed-control concepts permit speed ranges up to two–three times the base speed via voltage to frequency ($V$/$f$ ), that is, field-weakening control. This paper teaches the extension of the speed-control range up to nine times the base speed through online reconfiguration of the motor windings via electronic switches. The switchover of the windings, either from a winding with $p_{1}$ poles to $p_{2}$ poles, or from series to parallel connection of the number of turns per phase—so-called ($V$/ $N$·$f$) control—lasts less than a 60-Hz cycle. Such fast switchover causes small transients only, and therefore, this concept is applicable to most variable-speed drives.

37028

Hall D.  et.al 

Transient Electromechanical Modeling for Short Secondary Linear Induction Machines 

IEEE Transactions on Energy Conversion, Vo. 23; No. 3;  Sept. 2008; 789-795 

Linear induction motors are under development for a variety of demanding applications including aircraft launchers and magnetically levitating trains. These applications require machines that can produce large forces, operate at high speeds, and can be controlled precisely to meet performance requirements. The design and implementation of these systems require fast and accurate techniques for performing system simulation and control system design. We present techniques for modeling and controlling linear induction machines based on a direct and quadrature (DQ) representation of the system dynamics. Simulation results using the DQ representation of the machine dynamics are presented and compared to test data from a Subscale Integration Test Bed developed for the U.S. Navy's Electromagnetic Aircraft Launch System program.

37029

Boglietti A. et.al 

Induction Motor Equivalent Circuit Including the Stray Load Losses in the Machine Power Balance 

IEEE Transactions on Energy Conversion, Vo. 23; No. 3;  Sept. 2008; 796-803 

In this paper, the stray load losses due to the air gap spatial harmonics effects on the rotor squirrel cage are considered and a simplified induction motor equivalent circuit able to include them in the machine power balance is reported. In the proposed model, an additional resistance appears in series with the stator impedance. This additional parameter has been defined on the basis of power balance considerations applied to the induction motor classical theory. The complete theoretical analysis together with the guidelines to measure the equivalent circuit parameters are reported in detail. Finally, the proposed approach has been experimentally verified using five total enclosed fan cooled induction motors.

37030

Bueno, E.J.  et.al 

Design of a Back-to-Back NPC Converter Interface for Wind Turbines With Squirrel-Cage Induction Generator 

IEEE Transactions on Energy Conversion, Vo. 23; No. 3;  Sept. 2008; 932-945 

As the number of wind power applications with power electronic interfaces in the grid increases, it is becoming unacceptable to disconnect the generating units every time disturbances occur, especially under voltage dips, as was a common practice in the past. Keeping the converter online during unbalanced voltage, and guaranteeing the actual standards of the converter connected to the grid, is becoming a very critical issue. From these goals, the design of a robust back-to-back neutral point clamped (three levels) voltage source converter of 150 kVA is developed in this paper. The converter is divided into two main parts: the power electronic system and the control electronic system. Concerning the first part, on the one hand, the paper presents the designs of active and passive components as insulated gate bipolar transistor, free-wheeling diodes, clamping diodes, grid filter, dc-bus capacitors, etc.; and on the other hand, the converter requirements are analyzed to ride through real grid conditions, i.e., unbalanced voltage dips. Concerning the control electronic system, the chosen electronic structure and the task distribution between the two processors used are shown. 

37031

Fusco G.   & Russo M.   

Adaptive Voltage Regulator Design for Synchronous Generator 

IEEE Transactions on Energy Conversion, Vo. 23; No. 3;  Sept. 2008; 946-956 

This paper presents the adaptive design of an automatic voltage regulator (AVR) control scheme for synchronous generators that is capable of providing satisfactory voltage control performance in the presence of unknown variations of the power system operating conditions. The design is articulated in four steps: voltage and current phasor estimation, estimation of the parameters of the Thevenin equivalent circuit adopted to represent the power system response using a steady-state model, determination of the sampled-data transfer function of the system, and AVR design developed according to discrete-time techniques. A suitable procedure is described to derive the sampled-data transfer function of the system starting from models of the power system, synchronous generator, and exciter. The obtained transfer function depends on the estimated parameters yielded by a recursive least-squares algorithm subject to constraints deriving from the Thevenin circuit. The AVR design is based on the pole-assignment technique while the phasors estimation is performed by two Kalman filters. Finally, the results of accurate numerical simulations conducted for a test network are reported, comparing the performance of the proposed adaptive control scheme to the one of a PID controller with fixed parameters.

37032

Liese M. &  Brown  M.   

Design-Dependent Slot Discharge and Vibration Sparking on High Voltage Windings 

IEEE Transactions on Dielectrics and Electrical Insulation, Vol.15; No.4; August 2008; 927-932 

Partial discharge effects are widely acknowledged as a damage mechanism for deteriorating high voltage windings of electrical machines. Vibration sparking is another but scarcely known. Not only is vibration sparking significantly more damaging to electrical machine windings, unlike partial discharge deterioration it can occur at any position within the winding. Deteriorated winding insulation at the low voltage ends can only be detected via offline monitoring as online monitoring is not sufficient. Prevention of vibration sparking requires a reliably earthed outer corona layer of the winding bars or sufficiently large resistances of the outer corona layers. However the slot design needs to take account of both vibration sparking and partial discharge in order to mitigate these deterioration mechanisms.

37033

H. V. K. Shetty, A. M. Parikh and Vijayraj 

A Review of Recent Developments in Arial flux Permanent magnet machines. 

Electrical India, Vol. 48, No. 11, Nov 2008, P 224 

Axial flux permanent magnet (PM) machines, in the range 1.0 – 200 kW are being developed for many application such as wind turbines, traction, lifts, pumps, conveyors etc.  due to their attractive features.  A vast literature exists elaborating various topologies of axial PM machines.  An overview of developments of axial flux machines is presented in this paper wherein the advantages of axial flux over radial flux machin e have been highlighted.

37034

Pedra, J.  

On the Determination of Induction Motor Parameters From Manufacturer Data for Electromagnetic Transient Programs

IEEE Transactions on Power Systems, Vo. 23; No. 4;  Nov. 2008; 1709-1718

In this paper, an inaccuracy of the method for induction motor parameter determination used in EMTP type simulation programs (ATP, EMTP96, EMTDC) is discussed. The paper presents a numerical method for the estimation of induction motor double-cage model parameters from standard manufacturer data, i.e., full load mechanical power (rated power), full load power factor, maximum torque, starting torque, starting current and full load efficiency. The nonlinear equations to obtain the motor parameters have been solved with a modified Newton method that always converges if the problem is well defined (that is, a solution exists). The method has been tested with 608 motors from different manufacturers. The manufacturer parameters that have a greater influence on convergence are the maximum torque and the starting current. The cases where the method does not converge have been studied and the range of variation of the maximum torque or starting current which determines where the data are well defined (that is, a solution exists) has been calculated.

37035

Liu Z.J.   &  Li J.T.  

Accurate Prediction of Magnetic Field and Magnetic Forces in Permanent Magnet Motors Using an Analytical Solution

IEEE Transactions on Energy Conversion, Vo. 23; No. 3;  Sept. 2008; 717-726

This paper presents an analytical model suitable for analyzing permanent magnet motors with slotted stator core. By including the effect of the interaction between the pole transitions and slot openings, the model is able to predict the airgap field and magnetic forces with high accuracy, which cannot be achieved using the previously available analytical methods. The results of electromagnetic forces, i.e., the cogging torque and unbalanced magnetic pull, computed analytically agree well with numerical simulations using the finite-element method. The model is used to analyze the magnetic forces developed in permanent magnet brushless motors when the design parameters vary in wide ranges. The model is useful in design and optimization of permanent magnet motors.

37036

Wei Hua  et.al 

Analysis and Optimization of Back EMF Waveform of a Flux-Switching Permanent Magnet Motor 

IEEE Transactions on Energy Conversion, Vo. 23; No. 3;  Sept. 2008; 727-733 

Flux-switching permanent magnet (FSPM) motors have a doubly salient structure, the magnets being housed in the stator and the stator winding comprising concentrated coils. They have attracted considerable interest due to their essentially sinusoidal phase back electromotive force (EMF) waveform. However, to date, the inherent nature of this desirable feature has not been investigated in detail. Thus, a typical three-phase FSPM motor with 12 stator teeth and ten rotor poles is considered. It is found that, since there is a significant difference in the magnetic flux paths associated with the coils of each phase, this results in harmonics in the coil back EMF waveforms being cancelled, resulting in essentially sinusoidal phase back EMF waveforms. In addition, the influence of the rotor pole-arc on the phase back EMF waveform is evaluated by finite-element analysis, and an optimal pole-arc for minimum harmonic content in the back EMF is obtained and verified experimentally.

37037

Bayindir R. Et.al

Fault Detection and Protection of Induction Motors Using Sensors

IEEE Transactions on Energy Conversion, Vo. 23; No. 3;  Sept. 2008; 734-741

Protection of an induction motor (IM) against possible problems, such as overvoltage, overcurrent, overload, overtemperature, and undervoltage, occurring in the course of its operation is very important, because it is used intensively in industry as an actuator. IMs can be protected using some components, such as timers, contactors, voltage, and current relays. This method is known as the classical method that is very basic and involves mechanical dynamic parts. Computer and programmable integrated circuit (PIC) based protection methods have eliminated most of the mechanical components. However, the computer-based protection method requires an analog-to-digital conversion (ADC) card, and the PIC-based protection method does not visualize the electrical parameters measured. In this study, for IMs, a new protection method based on a programmable logic controller (PLC) has been introduced. In this method, all contactors, timers, relays, and the conversion card are eliminated. Moreover, the voltages, the currents, the speed, and the temperature values of the motor, and the problems occurred in the system, are monitored and warning messages are shown on the computer screen. Experimental results show that the PLC-based protection method developed costs less, provides higher accuracy as well as safe and visual environment compared with the classical, the computer, and the PIC-based protection systems.

37038

Samoylenko N et.al 

Dynamic Performance of Brushless DC Motors With Unbalanced Hall Sensors 

IEEE Transactions on Energy Conversion, Vo. 23; No. 3;  Sept. 2008; 752-763 

Brushless dc (BLDC) motors controlled by Hall-effect sensors are widely used in various applications and have been extensively researched in the literature, mainly under the assumption that the Hall sensors are ideally placed 120 electrical degrees apart. However, this assumption is not always valid; in fact, sensor placement may be significantly inaccurate, especially in medium- and low-precision BLDC machines. This paper shows that misplaced Hall sensors lead to unbalanced operation of the inverter and motor phases, which increases the low-frequency harmonics in torque ripple and degrades the overall drive performance. The paper also presents several average-filtering techniques that can be applied to the original Hall-sensor signals to mitigate the effect of unbalanced placement during steady-state and transient operations. The proposed methodology is demonstrated by modeling and hardware, and is shown to achieve dynamic performance similar to that of a BLDC motor with accurately positioned Hall sensors.

37039

Kyo-Beum Lee   & Blaabjerg F.   

Simple Power Control for Sensorless Induction Motor Drives Fed by a Matrix Converter 

IEEE Transactions on Energy Conversion, Vo. 23; No. 3;  Sept. 2008; 752-763 

This paper presents a new and simple method for sensorless control of matrix converter drives using a power flowing to the motor. The proposed control algorithm is based on controlling the instantaneous real and imaginary powers into the induction motor. To improve low-speed sensorless performance, the nonlinearities of a matrix converter drive such as commutation delays, turn-ON and turn-OFF times of switching devices, and on-state switching device voltage drop are modeled using a PQ power transformation and compensated using a reference power control scheme. The proposed sensorless control method is applied for the induction motor drive using a 3 kW matrix converter system. Experimental results are shown to illustrate the feasibility of the proposed strategy.

37040

Jong-Wook Kim   

On-Load Motor Parameter Identification Using Univariate Dynamic Encoding Algorithm for Searches 

IEEE Transactions on Energy Conversion, Vo. 23; No. 3; Sept. 2008;  804-813 

Parameter identification of an induction motor has long been studied either for vector control or fault diagnosis. This paper addresses parameter identification of an induction motor under on-load operation. For estimating electrical and mechanical parameters in the motor model from the on-load data, unmeasured initial states and load torque profile have to be also estimated for state evaluation. Since gradient of cost function for the auxiliary variables are hard to be derived, direct optimization methods that rely on computational capability should be employed. In this paper, the univariate dynamic encoding algorithm for searches (uDEAS), recently developed by the authors, is applied to the identification of whole unknown variables with measured voltage, current, and velocity data. Profiles of motor parameters estimated with uDEAS are reasonable, and estimation time is 2 s on average, which is quite fast as compared with other direct optimization methods.

37041

Guha S.  &  Kar N.C.   

Saturation Modeling and Stability Analysis of Synchronous Reluctance Generator 

IEEE Transactions on Energy Conversion, Vo. 23; No. 3; Sept. 2008;  814-823 

A new method of representing magnetic saturation in synchronous reluctance generator has been proposed in this paper. A linearized model of synchronous reluctance generator has been developed applying the proposed saturation model to perform the steady-state stability analysis. The effect of $d$ - and $q$-axis saturation on the steady-state stability of a synchronous reluctance generator has been investigated using the proposed linearized machine model. Effects of different loading conditions such as active power, reactive power, and power factor on the steady-state stability have also been looked into. Moreover, the effect of $d$- and $q$-axis saturation on the transient stability analysis has been investigated in the case of a three-phase symmetrical ground fault at the machine terminals.

37042

Valenciaga F.  et.al 

High-Order Sliding Control for a Wind Energy Conversion System Based on a Permanent Magnet Synchronous Generator 

IEEE Transactions on Energy Conversion, Vo. 23; No. 3; Sept. 2008;  860-867 

This paper presents the output power control of a wind energy conversion system (WECS) based on a permanent magnet synchronous generator (PMSG). It is assumed that the considered wind module integrates a stand-alone hybrid generation system, jointly with a battery bank, a variable ac load, and other generation subsystems. The operation strategy of the hybrid system determines two possible operation modes for the WECS, depending on the power requirements of the load and the wind availability. The paper deals with the design of a combined high-order sliding mode (HOSM) controller for the power control of the WECS on both operational modes. The main features of the obtained controller are its chattering-free behavior, its finite-time reaching phase, its simplicity, and its robustness with respect to external disturbances and unmodeled dynamics. The performance of the closed-loop system is assessed through representative computer simulations.

37043

Cavallini A.  et.al 

A Novel Method to Diagnose PWM-fed Induction Motors 

IEEE Transactions on Dielectrics and Electrical Insulation, Vol.15; No.5; October 2008; 1313-1321 

A novel method for measurement and interpretation of PD phenomena in inverter-fed motors is discussed in this paper. The interpretation of PD measurements is carried out resorting to the direct-quadrature (dq) transform of the three voltages at motor terminals at the instant a PD event occurs. New tools (the dq loci, dq Hq and dq Hn patterns) are proposed to infer PD activity in a statistical way, similar to that used under AC supply. The method has been validated through tests on motorettes. In addition, measurements on low-voltage inverter-fed motors subjected to repetitive surges till breakdown are reported to support the capability of the method to infer onsetting faults. Measurements are performed through a reliable and lightweight (thus suitable for, e.g., automotive or avionics applications) antenna coupler characterized by excellent signal-to-nose ratio.

37044

Xiang Peng  et.al 

New Method for Stator Slot Wedge Testing of Large Generators 

IEEE Transactions on Dielectrics and Electrical Insulation, Vol.15; No.4; August 2008; 933-940 

When large generators become operational, the stator bars in the slots are subjected to the electromagnetic force during normal operation. After the generators have been operating for a long time, the electromagnetic force may cause the stator bars to vibrate due to the existence of loose stator slot wedges in large generators. This leads to mechanical abrasion of the groundwall insulation and accelerates the deterioration of the generator, and can even cause generators to fail if the slot wedges are not treated. In order to ensure large generators continue working reliably, it is essential to detect loose slot wedges in the stator slots. This paper describes the modeling of slot wedges with different fixing styles in large generators to study the process by which slot wedges become loose, and also presents an analysis of the looseness of slot wedges based on their vibration characteristics corresponding to the loosening process of the stator slot wedge. Moreover, a series of tests were performed with a nondestructive detection system developed based on this analysis to check the tightness of slot wedges in the laboratory. The results showed that loose stator slot wedges of large generators could be detected either by their vibration frequency or by their displacement amplitude. This verified the correctness of the slot wedge loosening process and the validity of the detection system. 

37045

Mohiddon Md.A.   & Yadav K.L.  

Effect of Calcium Doping on Dielectric and Pyroelectric Properties of PLZT 

IEEE Transactions on Dielectrics and Electrical Insulation, Vol.15; No.5; October 2008; 1236-1241 

Effect of calcium doping on structural, dielectric and pyroelectric properties of Pb0.92-xLa0.08Cax(Zr0.65Ti0.35)0.98O3 (PLCZT) composition derived by the solid state reaction method was studied. Rhombohedral perovskite phase was confirmed in all the PLCZT samples. Calcium doping did not show any structural change in PLCZT (8/65/35) up to 2.5 % doping, however grain size and crystallite size was found to increase up to 1%, but no systematic variation of transition temperature was found with Ca doping. P-E hysteresis loop parameters (Ec and Pr) and pyroelectric properties were found to decrease with Ca doping up to 1% and there after increased.

37046

Hirose Hideo Hikita et.al 

Diagnosis of Electric Power Apparatus using the Decision Tree Method 

IEEE Transactions on Dielectrics and Electrical Insulation, Vol.15; No.5; October 2008; 1252-1260  

To diagnose the electric power apparatus, the decision tree method can be a highly recommended classification tool because it provides the if-then-rule in visible, and thus we may have a possibility to connect the physical phenomena to the observed signals. The most important point in constructing the diagnosing system is to make clear the relations between the faults and the corresponding signals. Such a database system can be built up in the laboratory using a model electric power apparatus, and we have made it. The next important thing is the feature extraction. We used ø - V - n patterns and POW patterns for feature variables, and feature extraction is made by the extended moments, usual moments, and the parameters in the underlying distributions such as the generalized normal distribution and the Weibull distribution. By simple arrangements, we will be able to classify the faults and noise with high accuracy such that the misclassification rate is lower than 5%. If we set appropriate pre-processing procedure carefully, we might have a possibility of classification accuracy of less than 2%. Therefore, the decision tree with adequate feature extraction is considered to be a promising method as one of the classification tools.

37047

Rui-jin Liao  et.al 

Thermal Aging Micro-scale Analysis of Power Transformer Pressboard 

IEEE Transactions on Dielectrics and Electrical Insulation, Vol.15; No.5; October 2008; 1281-1287 

In order to analyze the thermal aging mechanism of the insulation paper inside the power transformer, a series of accelerated thermal aging tests were performed on pressboard. Subsequently, the Atomic Force Microscope (AFM) together with Scanning Electron Microscope (SEM) and X-ray Diffraction (X-RD) were utilized to observe the micro surface of the thermal-aged pressboard. The experiments and analysis indicate that either the links among the D-glucopyranose units or the hexagonal mesh structures of the D-glucopyranose units were broken under thermal stress; the number of D-glucopyranose units after 6 weeks of aging was 0.8-1 per nm2, only about one third of un-aged value. The wall of a cellulose cell was deteriorated and thinned by thermal stress. At the same time, the cracks expanded gradually on the surface of the cellulose, which shortened the average width of cellulose fiber from about 40 μ of un-aged sample to about 25 μ after 6 weeks of aging. Meanwhile, the relative crystallinity and the size of the crystallite in the pressboard decreased nonlinearly with the thermal aging time.

37048

Lamarre L.  & David E.   

Temperature Dependence of the Resistance of Modern Epoxy Mica Insulation of HV Rotating Machines 

IEEE Transactions on Dielectrics and Electrical Insulation, Vol.15; No.5; October 2008; 1305-1312 

This work presents the temperature dependence of the dielectric properties of two types of epoxy mica insulation systems. Polarization and depolarization currents, insulation resistance, capacitance and polarization index were measured over a temperature range of 20 to 100 °C on whole rotating machine stator bars. An analytical relationship of the correction of the resistance as a function of temperature was derived from the experimental results.

37049

Lan L. &  Gorur R.S.  

Computation of ac Wet Flashover Voltage of Ceramic and Composite Insulators 

IEEE Transactions on Dielectrics and Electrical Insulation, Vol.15; No.5; October 2008; 1346-1352 

This paper presents a theoretical method for calculating the flashover voltage of ceramic and composite insulators under wet conditions. The insulator surface is assumed to be clean. A 3-Dimensional computer package (Coulomb) was used to calculate the electric field of wet surfaces. The surface wettability has been varied from hydrophobic to hydrophilic using the Swedish Transmission Research Institute (STRI) method of classification. The calculated results are in good agreement with published data.

37050

Abderrazzaq M.H.   

Characterizing the Internal Strain in Composite Insulation under Dry and Wet Conditions 

IEEE Transactions on Dielectrics and Electrical Insulation, Vol.15; No.5; October 2008; 1353-1359 

This paper investigates the internal mechanical strain, developed within composite and polyester resin dielectrics, under dry and wet conditions. The paper characterizes this strain by a set of colored images, caused by relative retardation orthogonal components of the polarized white light used to illuminate the specimens in the microscope. An image-editing tool is used to analyze the structure of the strain-generated colors by assigning an intensity value to each pixel of the Red, Green and Blue components of the image. Each point in the image is identified by a set of three numbers ranging from 0 to 255. The Microsoft Excel is employed to process the results and to provide a simple comparison among various cases of the analyzed data. The change in the color map between dry and wet conditions for each examined specimen is used as an indicator of strain pattern variation, and consequently, as a tool to characterize the impact of water absorption on composites. This approach offers a quantitative data from strain images without a need for a complex mathematical procedure. On the other hand, the paper focuses on the resin as an absorber and transmitter of moisture, and tries to verify this hypothesis by subjecting the specimens of polyester resin, cast in different ways, to the same tests as that for the composite ones. Despite the dependence of the obtained results on the materials used and conditions applied, there is a clear effect of the moisture as an aging element on reducing the mechanical stress developed within the dielectric material.

37051

Andersson J.

Properties of Interfaces between Silicone Rubber and Epoxy

IEEE Transactions on Dielectrics and Electrical Insulation, Vol.15; No.5; October 2008; 1360-1367

An experimental set-up was designed for testing the impact of adhesion defects at interfaces between silicone rubber and epoxy in composite insulators. Test samples were aged in this set-up by discharges appearing under a presence of tangential electric field at the interfaces exposed to humid conditions. This combination of stresses simulated realistic conditions, in which ageing at the interface could possibly accelerate further deterioration of the adhesion between silicone rubber and epoxy. The test samples were prepared by joining both the materials with and without application of primer. Without the primer, bonding between epoxy and silicone rubber was reduced. The interfacial strength after the ageing was investigated by means of a modified peel test, whereas the changes of the dielectric properties were assessed by dielectric response measurements. Furthermore, the resulting degradation was analysed with infrared spectroscopy and optical microscopy. The analyses showed that the combined stresses affected to some extend both the epoxy and the silicone rubber. However, the interfacial mechanical strength was not reduced significantly, which is an indicator for possibility to tolerate existence of small interfacial defects in real composite insulators.

37052

Ali M. &  Hackam R.   

Effects of Saline Water and Temperature on Surface Properties of HTV Silicone Rubber

IEEE Transactions on Dielectrics and Electrical Insulation, Vol.15; No.5; October 2008; 1368-1378

Silicone Rubber (SIR) after immersion in saline solutions as a function of time (0 to 3000 h) at different temperatures is reported. The hydrophobicity is determined by measuring the static contact ¿ between the tangent to the droplet of distilled water and the horizontal surface of the HTV SIR. The conductivity of the saline solution was varied from 0.005 to 100 mS/cm and the temperature from 0 to 98 °C. The contact angle which gives a measure of the hydrophobicity of the surface decreased sharply during immersion. The contact angle decreased from the original value of 100±4.6° to low value of 15° after 3000 h of immersion at 98 °C in a solution of 0.005 mS/cm. The lower the conductivity, the larger was the decrease in the contact angle. The changes in the weight of the HTV SIR due to the uptake of water and the average surface roughness (ASR) are determined during the immersion. The increase/decrease in the weight and surface roughness of the HTV SIR are correlated with the contact angle and hence with the loss of hydrophobicity. The surface free energies Υsd, Υsh and Υs, the interfacial energy of HTV SIR and water Υsl, and the energy of adhesion Wsiof water on HTV SIR are determined as a function of time during the immersion and related to the loss of hydrophobicity.

37053

Kindersberger J. &  Lederle C.   

Surface Charge Decay on Insulators in Air and Sulfurhexafluorid ¿ Part I: Simulation 

IEEE Transactions on Dielectrics and Electrical Insulation, Vol.15; No.4; August 2008; 941-948 

The decay of surface charges on polymeric insulators in air and SF6 is studied. Surface charges decay by three mechanisms, by volume and surface resistivity of the insulator as well as by neutralization from the gas. These mechanisms are investigated. In particular the mechanism of gas neutralization is explained in detail. It is shown that within a certain volume ions generated by natural radiation lead to a neutralization of surface charges on specimens and can contribute significantly to surface charge decay. Relevant gas parameters like ion pair generation, ion mobility and ion-ion recombination coefficient are given for air and SF6. The decay of surface charges generated by corona discharge is simulated by taking the three mechanisms into consideration. The intention of the simulation is to quantify the effect of the individual mechanisms of the decay of surface charges and to provide the patterns needed to interpret the experimental result given in part II of this study.

37054

Kindersberger, J. & Lederle C.  

Surface Charge Decay on Insulators in Air and Sulfurhexafluorid ¿ Part II: Measurements

IEEE Transactions on Dielectrics and Electrical Insulation, Vol.15; No.4; August 2008; 949-957 

The decay of surface charges on polymeric insulators in air and SF6 is studied. Surface charge decay by three mechanisms, i.e. by volume and surface resistivity of the insulator as well as charge neutralization by gas ions has been simulated individually in part I. In this part the simulations of the surface charge decay are verified by experiments with insulating plates made of polytetrafluorethylen (PTFE), silicone rubber (SIR) and epoxy resin (EP). The surface charge distribution is generated by corona discharge and the charge decay is simulated by taking all three mechanisms into consideration. The influence of the test setup and particularly the size of the storage volumes on the charge decay are shown in air and SF6.

37055

Hikita M.  et.al 

Insulation Characteristics of Gas Mixtures including Perfluorocarbon Gas 

IEEE Transactions on Dielectrics and Electrical Insulation, Vol.15; No.4; August 2008; 1015-1022 

This paper describes discharge properties of N2 and CO2-based gas mixtures including a perfluorocarbon (PFC) gas such as CF4, C3F8 and c-C4F8 under non-uniform field. The mixture ratio between a base gas of N2 or CO2 and the additive PFC gas was fixed as 9:1; namely, 90%N2/10%PFC or 90%CO2/10%PFC gas mixture. The PFC gases have even smaller global warming potential (GWP) than SF6 gas and have good insulation properties as SF6 gas. Thus, PFC gas mixture is expected to be a SF6 substitute without highly pressurizing the gas over the conventional pressure of 0.5 to 0.6 MPa. In this study, in order to compare the partial discharge (PD) inception voltage VPD and breakdown voltage VB properties between N2 and CO2-based gas mixtures, as well as between the additive gas of PFC and SF6 gas, we investigated these properties of the gas mixtures with a needle to plane electrode under ac high voltage application. The gas pressure was changed from 0.1 to 0.6 MPa. As a result, it was found that VPD and VB characteristics of N2 and CO2-based gas mixtures differed considerably, especially the gas pressure dependence of VB (so-called the N shape characteristics). VB characteristics of N2-based gas mixture including c-C4F8 proved to be excellent within the test conditions over the wide gas pressure region, showing the maximum breakdown voltage. In terms of VPD properties, CO2-based gas mixture had an advantage over N2-based gas mixture due to higher VPD. Furthermore, we discussed the synergy effects of VPD and VB for N2 and CO2-based gas mixtures using the index Rn which was defined to- - quantify the degree of the effect. Rn for CO2-based gas mixture was higher than that of N2-based gas mixture.

37056

Goshima H. et.al 

Fundamental Insulation Characteristics of High-Pressure CO2Gas for Gas-Insulated Power Equipment - Effect of Coating Conductor on Insulation Performance and Effect of Decomposition Products on Creeping Insulation of Spacer – 

IEEE Transactions on Dielectrics and Electrical Insulation, Vol.15; No.4; August 2008; 1023-1030 

Currently, environmental problems such as global warming are important issues, and SF6 has been identified as a greenhouse gas with a long atmospheric lifetime. Therefore, in the long term, it is preferable to reduce the amount of SF6 used as an insulating gas. It is thus important to discuss the possibility of using more environmentally friendly gases as alternative insulation for gas-insulated apparatus. In this paper, we describe the fundamental insulation breakdown characteristics of high-pressure CO2 gas at gas pressures of up to 1.0 MPa under simulated practical conditions, including the insulation breakdown characteristics of a high-voltage conducto