The monograph deals with the issues of the impact of operational exposures on the transformers' internal structures and electrical machines. It also focuses on the possibility of assessing their condition using high-frequency methods. It presents, with reference to the literature on the subject, original results of the authors' own research, including: analyses of high-frequency and resonance phenomena occurring in the windings of transformers and electrical machines subjected to fast-changing voltage surges arising in electrical networks, experimental studies using high-frequency methods and computer simulation studies.
Monografia dotyczy zagadnień oddziaływania narażeń eksploatacyjnych na struktury wewnętrzne transformatorów i maszyn elektrycznych oraz możliwości oceny ich stanu metodami wysokoczęstotliwościowymi. Przedstawione zostały w niej, z uwzględnieniem literatury przedmiotu, oryginalne wyniki badań własnych autorów, w tym: analizy zjawisk wysokoczęstotliwościowych i rezonansowych występujących w uzwojeniach transformatorów i maszyn elektrycznych poddawanych działaniu szybkozmiennych udarów napięciowych powstających w sieciach elektrycznych, badania eksperymentalne z zastosowaniem metod wysokoczęstotliwościowych oraz komputerowe badania symulacyjne.
- Contents
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Summary 7
Streszczenie 8
Symbols and abbreviations 9
1. Modern condition assessment techniques 13
1.1. Exploitation stresses 14
1.2. Diagnostics methods of electrical equipment 15
1.2.1. Transformer diagnostics methods 16
1.2.2. Electrical machines diagnostics methods 18
2. Diagnostics based on high frequency analysis 20
2.1. High frequency analysis of transformers 21
2.2. High frequency analysis of machine windings 25
3. Modelling and simulations of windings for high frequency analysis 28
3.1. Introduction 28
3.2. General characteristic of digital models of windings 29
3.3. Model with distributed parameters of windings 33
3.3.1. Transients in time domain 33
3.3.2. Transients in frequency domain 35
3.4. Lumped parameters model 36
3.5. Multiconductor transmission line model 42
3.6. Parameters of equivalent circuit of windings 49
4. Transfer function based fault discrimination criteria 54
4.1. Introduction 54
4.2. Transfer function based analysis 58
4.3. Transfer function for the deformed transformer windings 61
4.4. Transfer function-based fault discrimination criteria 68
4.4.1. Theoretical basis 68
4.4.1.1. Experimental setup 75
4.4.1.2. Measurement results 77
4.5. Application of high frequency method to assessment of electrical machine winding failures 85
4.5.1. Asynchronous motor 86
4.5.2. Windmill generator winding 91
4.5.3. Results of numerical modelling 95
5. Very fast voltage stresses of transformers insulating systems 98
5.1. Very fast transients 99
5.2. Lightning impulse 100
5.3. Impact of vacuum circuit breakers 102
5.4. Steep frontwave mitigation methods 103
5.4.1. Traditional methods preventing fast transients impact on transformers 103
5.4.2. SmartChoke based transient suppression 104
5.5. Impact of impulse voltage steep-front 111
5.6. Impact of winding patterns 115
6. Analysis of transient voltage distributions in transformer windings at different voltage stimuli 122
6.1. Introduction 122
6.2. Transients in time domain 124
6.2.1. Initial distributions in transformer windings 124
6.2.2. Influence of oil temperature on voltage distributions in transformer windings 126
6.2.3. Initial voltage distributions in transformer windings at different voltage stimulus 127
6.2.3.1. Influence of winding construction on transients 134
6.2.3.2. Initial voltage distributions in windings of power transformer at ultra fast stresses 138
6.2.4. Influence of surge magnitude on transient voltages in windings 143
6.3. Frequency characteristics of voltages in windings at different insulation conditions 144
6.3.1. Model windings and measurement setup 144
6.3.2. Influence of oil temperature on frequency characteristics of transformer windings of different constructions 145
7. Impact of resonance overvoltages in transformers on internal insulation systems 152
7.1. Introduction 152
7.2. Investigations of internal overvoltages in the winding of 110 kV 153
7.3. Investigations of frequency dependences of overvoltages inside the winding 159
7.4. Internal overvoltages in the winding of 15 kV generated by selected stimulus 165
7.5. Simulation of resonance overvoltages in the transformer windings 167
7.6. Spatial resonances in windings 169
7.7. Analysis of selected damages of transformers caused by resonance overvoltages 172
8. Application of transfer function to recognition of resonance overvoltages in transformer winding 175
8.1. Introduction 175
8.2. Transfer based recognition of resonance overvoltage prone zones 176
8.3. Investigations of frequency dependences of overvoltages inside the windings 177
8.4. Transfer function based recognition of resonance overvoltage sensitive zones 179
8.5. Simulation of resonance overvoltages in the transformer windings 181
9. Transfer overvoltages and frequency signatures of windings for transformers with steel and amorphous core 184
9.1. Introduction 184
9.2. Characteristic of experimental transformers 185
9.3. Measurement results 188
9.3.1. The 20 kVA transformer with silicon steel core 188
9.3.2. The 160 kVA transformer with silicon steel core 191
9.3.3. The 33 kVA transformer with amorphous magnetic core 193
10. Assessment of manufacturing processes based on FRA 198
10.1. Introduction 198
10.2. Theory and measuring technique 198
10.3. Results of investigations 200
Literature 207
Index 221
