Power Transformer Condition Monitoring and Diagnosis

2018·61.5 MB·English

by  Ahmed Abu-Siada

IETENERGY ENGINEERING 104
Power Transformer Condition
Monitoring and Diagnosis
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Power Transformer Condition
Monitoring and Diagnosis
Edited by
Ahmed Abu-Siada
The Institution of Engineering andTechnology
PublishedbyTheInstitutionofEngineeringandTechnology,London,UnitedKingdom
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Contents
Abouttheeditor xi
Preface xiii
Listofacronyms xv
1 Dissolved gasanalysis, measurementsandinterpretations 1
CarlosGamez
1.1 Introduction 1
1.2 Insulating liquids 2
1.2.1 Mineral oil 3
1.3 The transformer as a chemical reactor 3
1.3.1 Gasproductionmechanisms 5
1.4 Oil analysis 7
1.4.1 Gaschromatography 8
1.5 Oil sampling 9
1.5.1 Bottle sampling 12
1.5.2 Syringe sampling 13
1.6 Interpretation techniques 14
1.6.1 Fault types 16
1.6.2 Techniques that rely onthe gas profile 17
1.6.3 Techniques that rely onratios 23
1.6.4 Techniques that rely onrates of change 28
1.6.5 Putting it all together 29
1.7 Future of oil analysis 33
1.7.1 Online monitors 33
1.7.2 Larger datasets 34
1.7.3 Analysis automation 34
References 35
2 Partial discharges: keysfor condition monitoring
anddiagnosisof powertransformers 39
Ricardo Albarrac´ın, Guillermo Robles, Jorge Alfredo Ardila-Rey,
AndreaCavallini and Renzo Passaglia
Abstract 39
2.1 Introduction 39
2.2 Dielectric materials used in power transformers 40
vi Power transformercondition monitoring and diagnosis
2.3 Effects of ageing ininsulation systems of power transformers 43
2.3.1 Thermal stress 43
2.3.2 Mechanical stress 45
2.3.3 Electrical stress 46
2.3.4 Ambient stress 48
2.4 Condition monitoring techniques in power transformers 49
2.4.1 Electrical measurements 49
2.4.2 Apparentcharge estimation: quasi-integration
and calibration 51
2.4.3 PDdetection in transformers 54
2.4.4 Unconventional methods of partial discharge
measurementsin power transformers 58
2.4.5 Methods of partial discharge analysis 63
2.5 Conclusions 77
Acknowledgements 78
References 79
3 Moisture analysis for power transformers 87
Bele´nGarc´ıa,AlexanderCe´spedes and Diego Garc´ıa
3.1 Introduction 87
3.2 Moisture in transformer insulation 88
3.2.1 Risksassociated to the presence of highlevels
of moisture in transformers 88
3.2.2 Sources of moisture contamination in transformers 89
3.3 Moisture dynamics in transformers 90
3.3.1 Adsorption and desorption of moisture in cellulosic
insulation 92
3.3.2 Moisture distribution within transformer solid insulation 94
3.3.3 Solubility of water in oil 95
3.3.4 Moisture equilibrium between paper and oil 96
3.3.5 Moisture equilibrium in alternative fluids 98
3.3.6 Moisture dynamics in a transformer under operation 100
3.4 Monitoring of moisture content in oil 101
3.4.1 Periodical sampling of oil 101
3.4.2 On-line measure of oil moisture with capacitive sensors 102
3.4.3 Interpretation of the moisture content of oil 104
3.5 Estimation of the moisture content of solid insulation
from moisture inoil measures 106
3.5.1 Determination of moisture content of paper
using the equilibrium charts 106
3.5.2 Improved methodologiestoestimate the moisture
content of paper from the measures of moisture
content of oil 107
Contents vii
3.6 Dielectric responsemethodsfor the estimation of moisture
in solid insulation 108
3.6.1 Theoretical principles 108
3.6.2 Frequency dielectric spectroscopy 110
3.6.3 Recovery voltage method 115
3.6.4 Polarisation and depolarisation currents 117
3.7 Conclusions, future trendsand challenges 119
References 120
4 AssessingDPvalue of apower transformer considering
thermal ageing andpaper moisture 125
Ricardo David Medina Velecela,Andres Arturo Romero Quete,
Enrique Esteban Mombello, Giuseppe Ratta´
and Diego Xavier Morales Jada´n
Abstract 125
4.1 Introduction and preliminary issues 126
4.2 State of the art 126
4.3 Theoretical framework 127
4.3.1 Paper as power transformer solid insulation
system 127
4.3.2 Paper degradation process 127
4.3.3 Degradation accelerators 129
4.3.4 Paper humidity 129
4.3.5 Assessingof depolymerization process 131
4.4 Proposedmethod 133
4.4.1 Problem description 133
4.4.2 Oil moisture estimation 133
4.4.3 New approach for degree or polymerization
assessing 134
4.5 Casestudy 135
4.5.1 Results 136
4.6 Conclusions 139
References 140
5 Frequency responseanalysis 143
Mehdi Bagheri and ToanPhung
Abstract 143
5.1 Introduction 143
5.2 Transformer winding deformation 144
5.2.1 Deformation types and short-circuit current 144
5.2.2 Transformer transportation causingactive part
displacement 146
viii Power transformercondition monitoring and diagnosis
5.3 Methods to recognize winding deformation 148
5.3.1 Short-circuit impedance 148
5.3.2 Transfer function 151
5.4 Sweep frequency response analysis 152
5.5 Standard connection methods 153
5.5.1 End-to-end measurement 153
5.5.2 Inductive interwinding measurements 153
5.5.3 Capacitive interwinding measurements 153
5.5.4 End-to-end short-circuit measurements 153
5.6 FRAsignature assessment 155
5.6.1 Visual assessment of FRAsignature 155
5.6.2 Statistical assessment of FRAsignature 162
5.7 Factors affectingfrequency response signature 166
5.7.1 Winding inductance, capacitance 166
5.7.2 Series capacitance under buckling 178
5.7.3 Shunt capacitance under buckling 178
5.7.4 Tap-changer 178
5.7.5 Paper insulation deterioration 183
5.7.6 Temperature and moisture content 187
5.8 Online transformer winding deformation diagnosis 199
5.8.1 Methods for online transformer active part
assessment 199
5.8.2 Online FRAsetup 203
5.8.3 Online FRA(OFRA)progressand influence
of bushing tap 205
References 207
6 Monitoring of power transformers bymechanical
oscillations 211
Michael Beltle
6.1 Introduction 211
6.2 Physics of mechanical oscillations 212
6.2.1 Oscillations of the core 212
6.2.2 Oscillations of the windings 213
6.3 Measurement of vibrations 214
6.3.1 Comparison of tank wall and in-oil measurement 216
6.4 Sensitivity of surface tank measurements 217
6.4.1 Laboratory setup 217
6.4.2 Field test: sensor positions 219
6.5 Superimposingeffects ontank wall measurements 220
6.5.1 Effects of on-loadtap-changer position 220
6.5.2 Effects of transformer load and operating temperature 221
6.6 Practical case studies 223
6.6.1 Mechanical oscillations over time 223
Contents ix
6.7 Behaviourof mechanical oscillations at DC superimposition 225
6.7.1 DC-couplingpath into power transformers 225
6.7.2 Saturation and its effect on magnetostriction 226
6.7.3 Test setup forDC superimposed effects 227
6.7.4 DC-detection usingvibration measurement 229
6.7.5 Dependency of DC-driven vibration and transformer
noise 231
6.7.6 Case studyon transformers impacted by DC 233
6.8 Conclusion 234
References 235
7 Lifecycle managementof power transformers
in anewenergy era 239
CarlosGamez
7.1 Introduction 239
7.2 Achanging landscape 240
7.2.1 Renewable energy sources 243
7.2.2 Energy storage 246
7.3 Impact onasset management strategies 246
7.3.1 Operation, maintenance and replacement
of ageing assets 247
7.4 The advent of artificial intelligence 248
7.5 Analysis automation as an aid to lifecycle management 251
7.5.1 Condition attributes 252
7.5.2 Measurements 253
7.5.3 Analysis rules 253
7.5.4 Implementation tool 254
7.6 The digital substation 254
7.6.1 Value proposition 254
7.6.2 Technical standards 255
7.6.3 Hardware and software technologies 255
7.6.4 Businessprocesses 256
7.7 Summary 256
References 257
8 Power transformer asset management andremnant life 259
NorazharAbu Bakar
Abstract 259
8.1 Introduction 259
8.2 Transformer health condition 261
8.3 Proposedapproach 263
8.4 Fuzzy-logic model development 264
8.4.1 Furan criticality 265
8.4.2 COratio criticality 267