condition assessment of high voltage insulation in power system equipment pdf

IET POWER AND ENERGY SERIES 53 Condition Assessment of High Voltage Insulation in Power System Equipment www.EngineeringBooksPDF.com Other volumes in this series: Volume Volume Volume Volume Volume 10 Volume 11 Volume 13 Volume 14 Volume 15 Volume 16 Volume 18 Volume 19 Volume 21 Volume 22 Volume 24 Volume 25 Volume 26 Volume 27 Volume 29 Volume 30 Volume 31 Volume 32 Volume 33 Volume 34 Volume 35 Volume 36 Volume 37 Volume 38 Volume 39 Volume 40 Volume 41 Volume 43 Volume 44 Volume 45 Volume 46 Volume 47 Volume 48 Volume 49 Volume 50 Volume 51 Volume 52 Volume 905 Power circuit breaker theory and design C.H Flurscheim (Editor) Industrial microwave heating A.C Metaxas and R.J Meredith Insulators for high voltages J.S.T Looms Variable frequency AC-motor drive systems D Finney SF6 switchgear H.M Ryan and G.R Jones Conduction and induction heating E.J Davies Statistical technjiques for high voltage engineering W Hauschild and W Mosch Uninterruptible power supplies J Platts and J.D St Aubyn (Editors) Digital protection for power systems A.T Johns and S.K Salman Electricity economics and planning T.W Berrie Vacuum switchgear A Greenwood Electrical safety: a guide to causes and prevention of hazards J Maxwell Adams Electricity distribution network design, 2nd edition E Lakervi and E.J Holmes Artificial intelligence techniques in power systems K Warwick, A.O Ekwue and R Aggarwal (Editors) Power system commissioning and maintenance practice K Harker Engineers’ handbook of industrial microwave heating R.J Meredith Small electric motors H Moczala et al AC–DC power system analysis J Arrillaga and B.C Smith High voltage direct current transmission, 2nd edition J Arrillaga Flexible AC Transmission Systems (FACTS) Y-H Song (Editor) Embedded generation N Jenkins et al High voltage engineering and testing, 2nd edition H.M Ryan (Editor) Overvoltage protection of low-voltage systems, revised edition P Hasse The lighting flash V Cooray Control techniques drives and controls handbook W Drury (Editor) Voltage quality in electrical power systems J Schlabbach et al Electrical steels for rotating machines P Beckley The electric car: development and future of battery, hybrid and fuel-cell cars M Westbrook Power systems of electromagnetic transients simulation J Arrillaga and N Watson Advances in high voltage engineering M Haddad and D Warne Electrical operation of electrostatic precipitators K Parker Thermal power plant simulation and control D Flynn Economic evaluation of projects in the electricity supply industry H Khatib Propulsion systems for hybrid vehicles J Miller Distribution switchgear S Stewart Protection of electricity distribution networks, 2nd edition J Gers and E Holmes Wood pole overhead lines B Wareing Electric fuses, 3rd edition A Wright and G Newbery Wind power integration: connection and system operational aspects B Fox et al Short circuit currents J Schlabbach Nuclear power J Wood Power system protection, volumes www.EngineeringBooksPDF.com Condition Assessment of High Voltage Insulation in Power System Equipment R.E James and Q Su The Institution of Engineering and Technology www.EngineeringBooksPDF.com Published by The Institution of Engineering and Technology, London, United Kingdom © 2008 The Institution of Engineering and Technology First published 2008 This publication is copyright under the Berne Convention and the Universal Copyright Convention All rights reserved Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act, 1988, this publication may be reproduced, stored or transmitted, in any form or by any means, only with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms of licences issued by the Copyright Licensing Agency Enquiries concerning reproduction outside those terms should be sent to the publishers at the undermentioned address: The Institution of Engineering and Technology Michael Faraday House Six Hills Way, Stevenage Herts, SG1 2AY, United Kingdom www.theiet.org While the authors and the publishers believe that the information and guidance given in this work are correct, all parties must rely upon their own skill and judgement when making use of them Neither the authors nor the publishers assume any liability to anyone for any loss or damage caused by any error or omission in the work, whether such error or omission is the result of negligence or any other cause Any and all such liability is disclaimed The moral rights of the authors to be identified as authors of this work have been asserted by them in accordance with the Copyright, Designs and Patents Act 1988 British Library Cataloguing in Publication Data James, R E Condition assessment of high voltage insulation in power system equipment - (Power & energy series; v 53) Electric insulators and insulation - Testing High Voltages I Title II Su, Q III Institution of Engineering and Technology 621.3’1937 ISBN 978-0-86341-737-5 Typeset in India by Newgen Imaging Systems (P) Ltd, Chennai Printed in the UK by Athenaeum Press Ltd, Gateshead, Tyne & Wear www.EngineeringBooksPDF.com Contents Preface xi Introduction 1.1 Interconnection of HV power system components 1.1.1 Alternating voltage systems 1.1.2 Direct-voltage systems 1.2 Insulation coordination 1.3 High-voltage test levels 1.3.1 Power-frequency voltages 1.3.2 Lightning-impulse voltages 1.3.3 Switching surges 1.3.4 Very fast transient tests (VFTT) 1.3.5 Direct-voltage tests 1.4 Power system developments 1.4.1 Reliability requirements 1.4.2 Condition of present assets 1.4.3 Extension of power system life 1.4.4 New systems and equipment 1.5 Future insulation monitoring requirements 1.6 Summary 1.7 References 1.8 Problems 2 10 13 13 14 14 14 15 15 15 16 16 17 17 17 18 Insulating materials utilized in power-system equipment 2.1 Review of insulating materials 2.1.1 Gases 2.1.2 Vacuum 2.1.3 Liquids 2.1.4 Solids 21 22 22 25 25 27 www.EngineeringBooksPDF.com vi Condition Assessment of High-Voltage Insulation 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 Characterization of insulation condition 2.2.1 Permittivity (ε) and capacitance (C) 2.2.2 Resistivity (ρ) and insulation resistance (IR) 2.2.3 Time constants 2.2.4 Dielectric dissipation factor 2.2.5 Partial discharges (PD) 2.2.6 Physical and chemical changes Modes of deterioration and failure of practical insulating materials 2.3.1 Dielectric losses 2.3.2 Partial discharges – sources, forms and effects 2.3.3 Ageing effects Electrical breakdown and operating stresses Development of insulation applications Summary References Standards related to insulating materials Problems 33 33 33 34 34 35 35 36 37 39 46 48 50 50 51 53 54 Introduction to electrical insulation design concepts 3.1 Overview of insulation design requirements 3.1.1 Electrical requirements 3.1.2 Physical limitations 3.1.3 Working environment 3.1.4 Mechanical requirements 3.1.5 Thermal conditions 3.1.6 Processing 3.1.7 Reliability 3.2 Electric stress distributions in simple insulation systems 3.2.1 Multiple dielectric systems 3.2.2 Edge effects 3.2.3 Multiple electrode configurations 3.3 Electric stress control 3.4 Summary 3.5 References 3.6 Problems 55 55 56 56 56 57 58 58 59 60 61 64 66 68 69 69 70 Insulation defects in power-system equipment: Part 4.1 Suspension and post insulators 4.1.1 Suspension (string) insulators 4.1.2 Post insulators 4.2 High-voltage bushings 4.3 High-voltage instrument transformers 4.3.1 Oil-impregnated current transformers 4.3.2 Dry-type current transformers 4.3.3 Capacitor-type voltage transformers – CVT 71 71 71 73 74 77 78 80 81 www.EngineeringBooksPDF.com List of contents 4.4 4.5 4.6 4.7 4.8 4.9 4.10 4.11 4.12 High-voltage power capacitors High-voltage surge arresters High-voltage circuit breakers Gas-insulated systems (GIS) High-voltage cables 4.8.1 Oil–paper cables 4.8.2 Extruded cables Summary References Standards related to Chapter Problems Insulation defects in power-system equipment: Part 5.1 Electrical rotating machines 5.1.1 Low-voltage motors 5.1.2 High-voltage machines 5.1.3 Possible insulation failure mechanisms in rotating machines 5.1.4 CIGRE summary of expected machine insulation degradation 5.1.5 Future of machine insulation 5.2 Transformers and reactors 5.2.1 Windings 5.2.2 Transformer insulation structures 5.3 Summary 5.4 References 5.5 Problems Basic methods for insulation assessment 6.1 Generation and measurement of test high voltages 6.1.1 Power-frequency voltages 6.1.2 High-frequency voltages 6.1.3 Very-low-frequency voltages (VLF) 6.1.4 Direct voltages 6.1.5 Hybrid test circuits 6.1.6 Lightning impulse voltages 6.1.7 Switching surge voltages 6.1.8 High-voltage equipment for on-site testing 6.2 Non-destructive electrical measurements 6.2.1 Insulation resistance (IR) measurements 6.2.2 Measurements of the dielectric dissipation factor (DDF) 6.2.3 Measurement of partial discharges by electrical methods 6.2.4 Dielectric response measurements www.EngineeringBooksPDF.com vii 82 83 84 86 87 87 90 93 93 95 96 97 97 97 98 100 103 103 104 104 106 118 118 120 121 122 122 127 128 128 129 129 133 133 135 135 137 140 147 viii Condition Assessment of High-Voltage Insulation 6.3 6.4 6.5 6.6 6.7 Physical and chemical diagnostic methods 6.3.1 Indicators of in-service condition of oil–paper systems 6.3.2 Analysis of SF6 samples from GIS 6.3.3 Surface deterioration of composite insulators 6.3.4 Water treeing in XLPE cable insulation 6.3.5 Ultrasonic methods for detection of partial discharges 6.3.6 Miscellaneous techniques Summary References Standards related to basic test methods Problems Established methods for insulation testing of specific equipment 7.1 Overhead line and substation insulators 7.1.1 Porcelain and glass insulators (overhead lines) 7.1.2 Ceramic and glass insulators (post type – indoor and outdoor) 7.1.3 Composite insulators for overhead lines (string and post units) 7.2 Overhead line and substation hardware 7.3 Surge arresters 7.4 Switchgear 7.4.1 Circuit breakers 7.4.2 Self-protected switchgear 7.4.3 Disconnectors (isolators) 7.4.4 Metal-enclosed switchgear 7.4.5 Transformer tap changers 7.5 Bushings 7.6 High-voltage instrument transformers 7.6.1 Current transformers 7.6.2 Inductive voltage transformers 7.6.3 Capacitor voltage transformers 7.7 High-voltage power capacitors 7.8 High-voltage rotating machines 7.8.1 Stator bars 7.8.2 Assembled machine 7.9 High-voltage cables 7.9.1 Oil-impregnated cables 7.9.2 Extruded cables 7.10 Distribution and power transformers 7.10.1 Power-frequency overvoltage withstand tests 7.10.2 Partial-discharge tests 7.10.3 Summary of transformer HV test requirements www.EngineeringBooksPDF.com 150 150 153 153 153 154 154 154 154 157 158 159 160 161 161 162 162 163 164 164 166 166 166 167 167 168 168 169 170 171 171 172 172 173 173 173 175 175 177 180 List of contents 7.11 7.12 7.13 7.14 7.15 7.16 7.10.4 Additional tests Dielectric testing of HVDC equipment Miscellaneous items Summary References Standards related to Chapter Problems ix 182 182 184 184 184 185 188 Sensors for insulation condition monitoring 8.1 Ultra-high-frequency sensors 8.2 Optical-fibre sensors 8.2.1 Basic physics of optical-fibre sensing 8.2.2 Optical-fibre PD sensors 8.2.3 Optical-fibre temperature sensors 8.2.4 Advantages and disadvantages of optical-fibre sensors 8.3 Directional sensors for PD measurements 8.3.1 Directional coupler sensor 8.3.2 Directional field sensor 8.4 Summary 8.5 References 8.6 Problems 189 189 190 193 194 196 Online insulation condition monitoring techniques 9.1 The main problems with offline condition monitoring 9.2 Noise-mitigation techniques 9.2.1 Noise gating 9.2.2 Differential methods 9.2.3 Noise identification by signal waveform analysis 9.2.4 Multiple terminal PD measurements 9.3 Non-electrical online condition monitoring 9.3.1 Temperature monitoring of the insulations 9.3.2 Online DGA 9.3.3 Acoustic-based techniques for PD detection 9.4 Online acoustic/electric PD location methods for transformers 9.4.1 Acoustic transducers and winding terminal measurements 9.4.2 Application of internal combined acoustic and VHF/UHF transducers 9.5 Electrical online condition monitoring 9.5.1 Online dielectric dissipation factor and capacitance measurements 9.5.2 Online leakage current measurement 9.5.3 Electrical online PD detection 9.6 Summary 207 207 208 209 211 214 215 219 219 219 222 224 www.EngineeringBooksPDF.com 199 200 200 201 203 203 205 224 224 225 227 228 230 236 Artificial-intelligence techniques 263 discussed in this chapter, the maintenance schedule can be optimized and a longer service life in HV equipment and cables achieved This would delay the investment in new equipment and, at the same time, keep the network performance at an acceptable level The fault-diagnosis technique has been implemented in a computer program ICM-2.0 with a large data-storage capacity With a PC Pentium IV 2.0 GHz, the analysis of each set of DGA results takes about second The program also has a user-friendly interface and has been used by several utilities in Australia and New Zealand 10.5 References Dornerburg, E., Strittmatter, W., ‘Monitoring oil cooling transformers by gas analysis’, Brown Boveri Review, May 1974;61:238–47 Kelly, J.J., ‘Transformer fault diagnosis by gas-gas analysis’, IEEE Transactions on Industry Applications, December 1980;16(4):777–82 Rogers, R., ‘IEEE and IEC codes to interpret incipient faults in transformer, using gas in oil analysis’, IEEE Transactions on Electrical Insulation, October 1978;13(5):349–54 Lin, C E., Ling, J M., and Huang, C L., ‘An expert system for transformer fault diagnosis and maintenance using dissolved gas analysis’, IEEE Transactions on Power Delivery, January 1993;8(1):231–38 Tomsovic, K., Tapper, M., and Ingvarsson, T., ‘A fuzzy information approach to interpreting different transformer diagnostic methods’, IEEE Transactions on Power Delivery, July 1993;8(3):1638–46 Huang, Y.C., Yang, H.T., and Huang, C.L., ‘Developing a new transformer diagnosis system through evolutionary fuzzy logic’, IEEE Transactions on Power Delivery, April 1997;12(2):761–7 Wang, Z., Liu, Y., and Griffin, P.J., ‘A combined ANN and expert system tool for transformer fault diagnosis’, presented at the IEEE PES Winter Meeting, PE-411-PWRD-0-12-1997, New York, February 1998 IEC 60599-1999, ‘Interpretation of the analysis of gases in transformers and other oil-filled electrical equipment in-service’ Zadeh L., Fuzzy Sets, Information and Control, vol (Academic Press, New York, 1965), pp 338–53 10 IEEE Std C57.104-1991, IEEE Guide for the Interpretation of Gases Generated in Oil-Immersed Transformers, Transformer Committee of IEEE PES, 1991 11 Bell, S.R., The Cauchy Transform, Potential Theory, and Conformal Mapping (CRC Press, Boca Raton, Fl., 1992) 12 Su Q., and Mi, C., ‘Fuzzy diagnosis of transformer and generator faults’, presented at AUPEC’96, Melbourne University, Melbourne, October 1996, pp 389–94 13 Su, Q., Mi, C., et al., ‘A fuzzy dissolved gas analysis method for the diagnosis of multiple incipient faults in a transformer’, IEEE Transactions on Power Systems, May 2000;15(2)593–598 264 Condition Assessment of High-Voltage Insulation 14 Su, Q., ‘Reliability centered maintenance of electrical plant – some important issues’, presented at AUPEC’97, UNSW, Sydney, September–October 1997, pp 615–20 15 Su, Q., ‘Insulation condition assessment of large generators’, presented at the International Power and Energy Conference, Melbourne, 1999, pp 123–8 10.6 Problems Based on the fuzzy-logic method explained in this chapter, derive the IEC ratio codes and calculate the fuzzy logic elements F(0)…F(7) for the transformers whose DGA test results are given in the following table Fill in the derived and calculated results in the following tables No H2 CH4 C2 H C H4 C H6 95 120 300 110 17 490 0.1/0.2 mm Chapter Q.1: Q.2: Q.3: Q.4: (i) Speed differences Internal water cooling in large turbine generators (ii) Semiconducting tapes or similar (iii) Refer to Chapter Air stress due to applied voltage following local erosion of the earthed screen = 6.6 kVpk/mm The 0.5 mm air gap b/d = 5.4 kVpk/mm thus PDs are possible Hydrogen stress in gap for b/d = 10 kVpk/mm, thus applied voltage required for PDs = 9.6 kV (RMS) to ground (ii) From equation (Figure 5.4) for α = voltage across line end discs = 11% of line voltage For α = voltage is 26 per cent of line voltage Oil b/d stress for mm gap = 25 kV/mm (Figure 2.3(c)) requiring a voltage between the line discs of 225 kV For α = line voltage expected to cause b/d = 225 × 100/11 = 2049 kV Assuming safety factor of approximately 1.3 choose test level