Quality Confirmation Tests for Power Transformer Insulation Systems

by Behrooz Vahidi, Ashkan Teymouri

Overview

This book focuses on oil-paper insulation included in power transformers, especially for EHV and UHV transformers. The importance on insulation ever increased due to a growing voltage rating of transformers. Within the last decades, although research on the transformer insulation and diagnosis methods has advanced a lot, the insulation of HV transformers remained more or less unchanged. The book is divided into five chapters; the first and second chapters explain the basics of oil insulation, while the third chapter focuses on paper insulation. The final two chapters deal with the methods and outcome of testing both techniques. The primary target audience for this book is graduate students and power system engineers.

Product Details

ISBN-13:	9783030196929
Publisher:	Springer International Publishing
Publication date:	05/28/2019
Edition description:	1st ed. 2019
Pages:	107
Product dimensions:	6.10(w) x 9.25(h) x (d)

About the Author

Behrooz Vahidi was born in Abadan, Iran. He received the B.S. degree in electrical engineering from Sharif University of Technology, Tehran, Iran, the M.S. degree in electrical engineering from Amirkabir University of Technology, Tehran, Iran, and the Ph.D. degree in electrical engineering from the University of Manchester Institute of Science and Technology, U.K. From 1980 to 1986 he worked in industry as a Chief Engineer in the field of high voltage. Since 1989 he has been with the Department of Electrical Engineering, Amirkabir University of Technology, where he is currently a Professor. He was selected as the Distinguished Researcher of Iran by the Ministry of Higher Education of Iran in 2011, and by the Iranian Association of Electrical and Electronics Engineers in 2012. He has authored or coauthored more than 450 papers, and one book (in Persian) on high-voltage engineering and power systems. His main fields of research are high voltage, electrical insulation, power system transients, lightning protection, and pulsed-power technology.

Ashkan Teymouri was born in Zanjan, Iran. He received the B.Sc. degree in Electrical Engineering from K.N.Toosi University of Technology, Tehran, Iran. He received the M.Sc. degree In Power System from Amirkabir University of Technology Tehran, Iran. Currently he is a Ph.D. student in Electrical Engineering (power system) at Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran. He collaborates with the Iran Transfo Company, Zanjan, Iran.

Table of Contents

Contents

Chapter 1: Unused Mineral Insulating Oil

1.1..... Introduction. 2

1.2..... Mineral Oil 2

1.3..... Classification of mineral oil based on application 3

1.3.1...... Transformers oil 4

1.3.2...... Switchgear oil in low temperatures 4

1.4..... Additives. 9

1.5..... Special cases. 11

1.6..... Analysis of potentially corrosive sulphur 11

1.7..... Oil contamination 12

References. 12

Chapter 2: In-service Mineral Insulating Oil

2.1..... Introduction. 14

2.2..... Oil monitoring and purification 14

2.3..... Oil ageing and degradation 15

2.4..... Oil tests. 15

2.4.1...... Color and appearance 15

2.4.2...... Breakdown voltage 16

2.4.3...... Water content 16

2.4.4...... Water in the insulation system 17

2.4.5...... Acidity. 21

2.4.6...... Dielectric dissipation factor (DDF) and resistivity 21

2.4.7...... Additives and oxidation stability 24

2.4.8...... Sludge and sediment 25

2.4.9...... Interfacial tension 25

2.4.10.... Particle content 25

2.4.11.... Flash point 27

2.4.12.... Compatibility of insulating oil 27

2.4.13.... Pour point 28

2.4.14.... Density. 28

2.4.15.... Viscosity. 28

2.4.16.... PCB.. 28

2.4.17.... Corrosive sulphur 28

2.4.18.... Dibenzyl disulphides (DBDS) 29

2.4.19.... Passivators. 29

2.5..... In-service oil monitoring 30

2.5.1...... Uninhibited oil monitoring 30

2.5.2...... Inhibited oil monitoring 30

2.6..... Time schedule of sampling and testing in-service oil 31

2.7..... Available on-site tests 31

2.8..... Classification of operating oil 32

2.9..... Corrective actions 32

2.10... Purification. 32

2.10.1.... Physical purification 33

2.10.2.... Chemical purification (refinement) 35

2.10.3.... Substitution of additives 36

2.10.4.... Cleaning PCB contaminated oil 36

2.11... Replacing oil in electrical equipment 36

2.12... Adding passivators 37

2.13... Determining water concentration in the oil 38

References. 39

Chapter 3: Chemical Indicators

3.1..... Introduction. 42

3.2..... Insulation paper life determination 42

3.3..... Cellulose. 43

3.4..... Cellulose molecular structure 44

3.5..... Cellulosic insulation 44

3.6..... Degree of polymerization 46

3.7..... Oil impregnated insulation paper 47

3.8..... Ageing of oil impregnated insulation paper 47

3.9..... Ageing mechanism.. 48

3.9.1...... Pyrolysis. 49

3.9.2...... Hydrolysis. 50

3.9.3...... Oxidation. 51

3.10... Influence from acids 52

3.11... Ageing of oil 52

3.12... Oil oxidation. 53

3.13... Degradation products in oil impregnated insulation systems 53

3.14... Degradation products from cellulosic insulation 54

3.14.1.... Water 54

3.14.2.... Acids. 54

3.14.3.... Furans. 54

3.14.4.... Carbon oxides 55

3.14.5.... Hydrocarbons 55

3.15... Degradation products of oil 56

3.15.1.... Acids. 56

3.15.2.... Sludge. 56

3.16... Chemical indicators 56

3.17... Furan compounds 57

3.17.1.... Furans origin. 57

3.18... The relationship between DP and furans 57

3.19... Stability. 58

3.20... Furans disadvantages 59

3.21... CO₂ and CO.. 59

3.22... The combination of CO₂/CO ratio and 2-furfural 60

3.23... Methanol 61

References. 69

Chapter 4: Dissolved Gas Analysis (DGA)

4.1..... Introduction. 74

4.2..... Total flammable dissolved gas in the transformer 76

4.3..... Allowable concentration of gases in a transformer 76

4.4..... Gas ratio methods 77

4.4.1...... Dürrenberg method 77

4.4.2...... Rogers ratio. 78

4.4.3...... IEC Ratio method 79

4.5..... Duval triangle method 80

4.6..... Detection of partial discharge using DGA 82

4.7..... Impact of DGA accuracy on fault detection 82

References. 83

Chapter 5: Other Tests

5.1..... Introduction. 86

5.2..... Partial discharge (PD) 86

5.2.1...... Corona discharge 87

5.2.2...... Surface discharge 87

5.2.3...... Discharge in composite insulation materials 88

5.2.4...... Electric discharge in cavities 88

5.2.5...... Electric treeing 89

5.3..... Partial discharge measurement 90

5.4..... Insulation monitoring by PD measurement 91

5.5..... Comparison of electrical and audio detection methods 94

5.6..... Partial discharge formation in transformers 95

5.7..... Dielectric response analysis 95

5.8..... Polarization. 96

5.9..... Polarization and depolarization currents 98

5.10... Insulation spectroscopy in time domain 99

5.11... FDS test 102

5.12... Returning voltage method 104

5.13... Isothermal relaxation current 106

5.14... Frequency response analysis (FRA) 107

5.15... Frequency response analysis theory 108

5.16... Application of FRA in power transformers 109

5.17... FRA test features 109

5.18... Frequency response measurement methods 110

5.18.1.... Swept frequency method (SFM) 110

5.18.2 Low voltage impulse methods (LVI) 112

5.19... Comparison of LVI and SFM methods 112

5.20... Detectable defects by FRA 113

References. 114

Subject Index. 117