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High Voltage Engineering - Fundamentals

552 Pages · 2004 · 4.48 MB · English

  • High Voltage Engineering - Fundamentals

    High Voltage Engineering


    Fundamentals High Voltage Engineering


    Fundamentals


    Second edition


    E. Kuffel


    Dean Emeritus,


    University of Manitoba,


    Winnipeg, Canada


    W.S. Zaengl


    Professor Emeritus,


    Electrical Engineering Dept.,


    Swiss Federal Institute of Technology,


    Zurich, Switzerland


    J. Kuffel


    Manager of High Voltage and Current Laboratories,


    Ontario Hydro Technologies,


    Toronto, Canada


    Newnes


    OXFORD AUCKLAND BOSTON JOHANNESBURG MELBOURNE NEWDELHI Newnes


    AnimprintofButterworth-Heinemann


    LinacreHouse,JordanHill,OxfordOX28DP


    225WildwoodAvenue,Woburn,MA01801-2041


    AdivisionofReedEducationalandProfessionalPublishingLtd


    Firstpublished1984byPergamonPress


    Reprinted1986


    Secondedition2000,publishedbyButterworth-Heinemann


    uf6d9E.KuffelandW.S.Zaengl1984


    uf6d9E.Kuffel,W.S.ZaenglandJ.Kuffel2000


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    ISBN0750636343


    TypesetbyLaserWords,Madras,India


    PrintedinGreatBritain Contents


    Preface to second edition xi


    Preface to first edition xv


    Chapter 1 Introduction 1


    1.1 Generation and transmission of electric energy 1


    1.2 Voltagestresses 3


    1.3 Testing voltages 5


    1.3.1 Testing with power frequency voltages 5


    1.3.2 Testing with lightningimpulsevoltages 5


    1.3.3 Testing with switchingimpulses 6


    1.3.4 D.C. voltages 6


    1.3.5 Testing with very low frequency voltage 7


    References 7


    Chapter 2 Generation of high voltages 8


    2.1 Direct voltages 9


    2.1.1 A.C. to D.C. conversion 10


    2.1.2 Electrostaticgenerators 24


    2.2 Alternatingvoltages 29


    2.2.1 Testing transformers 32


    2.2.2 Series resonant circuits 40


    2.3 Impulse voltages 48


    2.3.1 Impulse voltage generator circuits 52


    2.3.2 Operation, design and construction of impulse generators 66


    2.4 Control systems 74


    References 75


    Chapter 3 Measurement of high voltages 77


    3.1 Peak voltage measurements by spark gaps 78


    3.1.1 Sphere gaps 79


    3.1.2 Reference measuring systems 91 vi Contents


    3.1.3 Uniform field gaps 92


    3.1.4 Rod gaps 93


    3.2 Electrostaticvoltmeters 94


    3.3 Ammeter in series with high ohmic resistors and high ohmic resistorvoltage


    dividers 96


    3.4 Generating voltmeters and field sensors 107


    3.5 The measurement of peak voltages 109


    3.5.1 The Chubb–Fortescue method 110


    3.5.2 Voltage dividers and passiverectifier circuits 113


    3.5.3 Active peak-reading circuits 117


    3.5.4 High-voltagecapacitors for measuring circuits 118


    3.6 Voltagedividingsystems and impulse voltagemeasurements 129


    3.6.1 Generalized voltagegeneration and measuring circuit 129


    3.6.2 Demands upon transfer characteristics of the measuring system 132


    3.6.3 Fundamentals for thecomputation of the measuring system 139


    3.6.4 Voltage dividers 147


    3.6.5 Interaction between voltagedivider and its lead 163


    3.6.6 The divider’s low-voltagearm 171


    3.7 Fast digital transient recorders for impulsemeasurements 175


    3.7.1 Principles and historical development of transient digitalrecorders


    176


    3.7.2 Errors inherent in digitalrecorders 179


    3.7.3 Specification of ideal A/D recorder and parameters required for h.v.


    impulse testing 183


    3.7.4 Future trends 195


    References 196


    Chapter 4 Electrostatic fields and field stress control 201


    4.1 Electrical field distributionand breakdown strength of insulatingmaterials


    201


    4.2 Fields in homogeneous, isotropicmaterials 205


    4.2.1 The uniform field electrode arrangement 206


    4.2.2 Coaxial cylindrical and spherical fields 209


    4.2.3 Sphere-to-sphere or sphere-to-plane 214


    4.2.4 Two cylindrical conductors in parallel 218


    4.2.5 Field distortionsby conducting particles 221


    4.3 Fields in multidielectric,isotropicmaterials 225


    4.3.1 Simple configurations 227


    4.3.2 Dielectric refraction 232


    4.3.3 Stress control by floating screens 235


    4.4 Numerical methods 241


    4.4.1 Finite difference method (FDM) 242 Contents vii


    4.4.2 Finite element method (FEM) 246


    4.4.3 Charge simulation method (CSM) 254


    4.4.4 Boundary element method 270


    References 278


    Chapter 5 Electrical breakdown in gases 281


    5.1 Classical gas laws 281


    5.1.1 Velocity distributionof a swarm of molecules 284


    5.1.2 The free path (cid:1) of molecules and electrons 287


    5.1.3 Distributionof free paths 290


    5.1.4 Collision-energy transfer 291


    5.2 Ionization and decay processes 294


    5.2.1 Townsend first ionizationcoefficient 295


    5.2.2 Photoionization 301


    5.2.3 Ionization by interaction of metastables with atoms 301


    5.2.4 Thermal ionization 302


    5.2.5 Deionization by recombination 302


    5.2.6 Deionization by attachment–negativeion formation 304


    5.2.7 Mobilityof gaseous ions and deionization by diffusion 308


    5.2.8 Relation between diffusion and mobility 314


    5.3 Cathode processes – secondary effects 316


    5.3.1 Photoelectric emission 317


    5.3.2 Electron emission by positiveion and excited atom impact 317


    5.3.3 Thermionic emission 318


    5.3.4 Field emission 319


    5.3.5 Townsend second ionization coefficient (cid:2) 321


    5.3.6 Secondary electron emission by photon impact 323


    5.4 Transitionfrom non-self-sustaineddischarges to breakdown 324


    5.4.1 The Townsend mechanism 324


    5.5 The streamer or ‘Kanal’ mechanism of spark 326


    5.6 The sparking voltage–Paschen’s law 333


    5.7 Penning effect 339


    5.8 The breakdown field strength (E ) 340


    b


    5.9 Breakdown in non-uniformfields 342


    5.10 Effect of electron attachment on the breakdown criteria 345


    5.11 Partial breakdown, corona discharges 348


    5.11.1 Positive or anode coronas 349


    5.11.2 Negative or cathode corona 352


    5.12 Polarity effect – influence of space charge 354


    5.13 Surge breakdown voltage–timelag 359 viii Contents


    5.13.1 Breakdown under impulsevoltages 360


    5.13.2 Volt–timecharacteristics 361


    5.13.3 Experimental studies of time lags 362


    References 365


    Chapter 6 Breakdown in solidand liquid dielectrics 367


    6.1 Breakdown in solids 367


    6.1.1 Intrinsicbreakdown 368


    6.1.2 Streamer breakdown 373


    6.1.3 Electromechanical breakdown 373


    6.1.4 Edge breakdown and treeing 374


    6.1.5 Thermal breakdown 375


    6.1.6 Erosion breakdown 381


    6.1.7 Tracking 385


    6.2 Breakdown in liquids 385


    6.2.1 Electronic breakdown 386


    6.2.2 Suspended solid particle mechanism 387


    6.2.3 Cavity breakdown 390


    6.2.4 Electroconvection and electrohydrodynamicmodel of dielectric


    breakdown 391


    6.3 Static electrification in power transformers 393


    References 394


    Chapter 7 Non-destructive insulation test techniques 395


    7.1 Dynamic properties of dielectrics 395


    7.1.1 Dynamic properties in the time domain 398


    7.1.2 Dynamic properties in the frequency domain 404


    7.1.3 Modelling of dielectricproperties 407


    7.1.4 Applications to insulationageing 409


    7.2 Dielectricloss and capacitance measurements 411


    7.2.1 The Schering bridge 412


    7.2.2 Current comparator bridges 417


    7.2.3 Loss measurement on complete equipment 420


    7.2.4 Null detectors 421


    7.3 Partial-discharge measurements 421


    7.3.1 The basic PD test circuit 423


    7.3.2 PD currents 427


    7.3.3 PD measuring systems within the PD test circuit 429


    7.3.4 Measuring systems for apparent charge 433


    7.3.5 Sources and reduction of disturbances 448


    7.3.6 Other PD quantities 450


    7.3.7 Calibration of PD detectors in a complete test circuit 452 Contents ix


    7.3.8 Digital PD instruments and measurements 453


    References 456


    Chapter 8 Overvoltages, testing procedures and insulation coordination 460


    8.1 The lightningmechanism 460


    8.1.1 Energy in lightning 464


    8.1.2 Nature of danger 465


    8.2 Simulated lightningsurges for testing 466


    8.3 Switching surge test voltage characteristics 468


    8.4 Laboratory high-voltagetesting procedures and statisticaltreatment of results


    472


    8.4.1 Dielectric stress–voltagestress 472


    8.4.2 Insulation characteristics 473


    8.4.3 Randomness of the appearance of discharge 473


    8.4.4 Types of insulation 473


    8.4.5 Types of stress used in high-voltagetesting 473


    8.4.6 Errors and confidence in results 479


    8.4.7 Laboratory test procedures 479


    8.4.8 Standard test procedures 484


    8.4.9 Testing with power frequency voltage 484


    8.4.10 Distributionof measured breakdown probabilities (confidence in


    measured P(cid:6)V(cid:8)) 485


    8.4.11 Confidence intervals in breakdown probability(in measured values)


    487


    8.5 Weightingof the measured breakdown probabilities 489


    8.5.1 Fitting of the best fit normal distribution 489


    8.6 Insulationcoordination 492


    8.6.1 Insulation level 492


    8.6.2 Statistical approach to insulationcoordination 495


    8.6.3 Correlation between insulationand protection levels 498


    8.7 Modern power systems protection devices 500


    8.7.1 MOA – metal oxide arresters 500


    References 507


    Chapter 9 Design and testing of external insulation 509


    9.1 Operation in a contaminated environment 509


    9.2 Flashover mechanism of polluted insulators under a.c. and d.c. 510


    9.2.1 Model for flashover of polluted insulators 511


    9.3 Measurements and tests 512


    9.3.1 Measurement of insulatordimensions 513 x Contents


    9.3.2 Measurement of pollutionseverity 514


    9.3.3 Contamination testing 517


    9.3.4 Contamination procedure for clean fog testing 518


    9.3.5 Clean fog test procedure 519


    9.3.6 Fog characteristics 520


    9.4 Mitigationof contamination flashover 520


    9.4.1 Use of insulatorswith optimized shapes 520


    9.4.2 Periodic cleaning 520


    9.4.3 Grease coating 521


    9.4.4 RTV coating 521


    9.4.5 Resistive glaze insulators 521


    9.4.6 Use of non-ceramic insulators 522


    9.5 Design of insulators 522


    9.5.1 Ceramic insulators 523


    9.5.2 Polymeric insulators(NCI) 526


    9.6 Testing and specifications 530


    9.6.1 In-service inspectionand failure modes 531


    References 531


    Index 533 Preface to Second Edition


    The first edition as well as its forerunnerof Kuffel and Abdullah published in


    1970andtheirtranslationsintoJapaneseandChineselanguageshaveenjoyed


    wide international acceptance as basic textbooks in teaching senior under-


    graduate and postgraduate courses in High-Voltage Engineering. Both texts


    havealsobeenextensivelyusedbypractisingengineersengagedinthedesign


    and operation of high-voltage equipment. Over the years the authors have


    received numerous comments from the text’s users with helpful suggestions


    forimprovements.Thesehavebeenincorporatedinthepresentedition. Major


    revisions and expansion of several chapters have been made to update the


    continued progress and developments in high-voltage engineering over the


    past two decades.


    As in the previous edition, the principal objective of the current text is to


    cover the fundamentals of high-voltage laboratory techniques, to provide an


    understanding of high-voltage phenomena, and to present the basics of high-


    voltage insulation design together with the analytical and modern numerical


    tools available to high-voltage equipment designers.


    Chapter 1 presents an introduction to high-voltage engineering including


    the concepts of power transmission, voltage stress, and testing with various


    typesofvoltage.Chapter2providesadescriptionoftheapparatususedinthe


    generation of a.c., d.c., and impulse voltages. These first two introductory


    chapters have been reincorporated into the current revision with minor


    changes.


    Chapter 3 deals with the topic of high-voltage measurements. It has under-


    gone major revisions in content to reflect the replacement of analogue instru-


    mentation with digitally based instruments. Fundamental operating principles


    of digital recorders used in high-voltage measurements are described, and the


    characteristicsofdigitalinstrumentationappropriateforuseinimpulsetesting


    are explained.


    Chapter 4 covers the application of numerical methods in electrical stress


    calculations. It incorporates much of the contents of the previous text, but the


    section on analogue methods has been replaced by a description of the more


    current boundary element method.


    Chapter 5 of the previous edition dealt with the breakdown of gaseous,


    liquid, and solid insulation. In the new edition these topics are described in


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