Preface ...................................................... xiii
Acknowledgments ................................................ xv
About the Author ............................................. xvii
1 The Basics ................................................... 1
1.1 Three-Phase History ..................................... 1
1.2 Three-Phase System Advantages ........................... 1
1.3 Theory .................................................. 2
1.4 Magnetism ............................................... 2
1.5 Voltage and Current ..................................... 5
1.6 Resistance .............................................. 7
1.7 Inductance .............................................. 8
1.8 Capacitance ............................................. 8
1.9 Circuits ................................................ 9
1.10 Time Constants ......................................... 10
1.11 Reactance .............................................. 12
1.12 Series Impedance ....................................... 13
1.13 Parallel Impedance ..................................... 17
1.14 Transformers ........................................... 19
1.15 Electrical Systems ..................................... 21
1.16 Generating Station Electrical Configurations ........... 22
1.17 Three-Phase Basics ..................................... 24
1.18 Power Transformer Connections .......................... 30
1.19 Instrument Transformer Connections ..................... 35
1.20 Bibliography ........................................... 37
2 Electrical Studies .......................................... 39
2.1 Conversions ............................................ 39
2.1.1 Ohmic ........................................... 39
2.1.2 Megavolt-Amps (MVA) ............................. 40
2.2 Transformer Tap Optimization ........................... 43
2.3 Conductor Parameters ................................... 45
2.3.1 Buses ........................................... 46
2.3.2 Insulated Cable ................................. 48
2.3.3 Overhead Aluminum Conductor Steel Reinforced
(ACSR) Cable .................................... 50
2.4 Study Accuracy ......................................... 53
2.5 Voltage Studies ........................................ 53
2.5.1 Bus Voltage Drop ................................ 53
2.5.2 Line Voltage Drop ............................... 53
2.5.1 Capacitive Voltage Rise ......................... 55
2.5.4 Collapsing Delta ................................ 55
2.6 Power Transfer Calculations ............................ 55
2.7 Two-Generator System ................................... 57
2.8 Ohmic Short Circuit Calculations ....................... 58
2.8.1 No Transformer .................................. 58
2.8.2 Parallel Sources ................................ 58
2.9 The Per-Unit System .................................... 59
2.9.1 Basic Formulas .................................. 60
2.9.2 Corrected Voltage Base .......................... 61
2.9.3 Per-Unit Z to Amps .............................. 61
2.9.4 Amps to Per-Unit R and X ........................ 63
2.9.5 New MVA Base .................................... 63
2.9.6 Per Unit to Ohms ................................ 64
2.9.7 Amps to Per-Unit Z .............................. 65
2.10 Per-Unit Short Circuit Calculations .................... 65
2.10.1 Transformer Short Circuits ...................... 65
2.10.2 Transformer Three-Phase and Phase-to-Phase
Fault Procedures ................................ 65
2.10.3 Sequence Impedances ............................. 70
2.10.4 Transformer Ground Fault Procedure .............. 71
2.10.5 Alternative Ground Fault Procedure .............. 73
2.10.6 Generator Three-Phase Short Circuits ............ 73
2.10.7 Generator De-Excitation ......................... 75
2.10.8 Motor Contribution .............................. 77
2.11 Bibliography ........................................... 78
3 Auxiliary System Protection ................................. 79
3.1 Switchgear Overcurrent Coordination .................... 79
3.2 Overcurrent Schematic .................................. 81
3.3 Current Transformer (CT) Safety Ground ................. 82
3.4 Motor Overcurrent ...................................... 83
3.5 Motor Control Center (MCC) Source Overcurrent .......... 87
3.6 Bus Tie Overcurrent .................................... 87
3.7 Transformer Secondary Side Overcurrent ................. 92
3.8 Transformer Primary Side Overcurrent ................... 92
3.9 Residual Ground Protection ............................. 94
3.10 High Impedance Grounding ............................... 96
3.10.1 Induced Voltages ................................ 97
3.10.2 Transient Voltage Mitigation .................... 99
3.10.3 Primary to Secondary Capacitive Coupling ....... 103
3.10.4 Neutral Grounding .............................. 103
3.10.5 Grounded Wye-Broken Delta Grounding ............ 106
3.11 Transformer High-Speed Protection ..................... 111
3.11.1 Current Differential Protection ................ 112
3.12 Bus Transfer Schemes .................................. 114
3.13 Bibliography .......................................... 118
4 Generator Protection ....................................... 119
4.1 Generator Relay Data .................................. 119
4.2 High Voltage Switchyard Configurations ................ 122
4.3 High Voltage Switchyard Protection Concerns ........... 125
4.4 Generator Protective Functions ........................ 128
4.4.1 Backup Impedance (21) .......................... 128
4.4.2 Volts/Hz (24) .................................. 131
4.4.3 Sync Check (25) ................................ 138
4.4.4 Reverse Power (32) ............................. 140
4.4.5 Loss of Field (40) ............................. 142
4.4.6 Negative Phase Sequence (46) ................... 146
4.4.7 Inadvertent Energization (50/27) ............... 149
4.4.8 Breaker Failure (50BF) ......................... 151
4.4.9 Pole Flashover (50NF) .......................... 152
4.4.10 Overvoltage (59) ............................... 153
4.4.11 Loss of Potential (60) ......................... 154
4.4.12 Stator Ground (64) ............................. 154
4.4.13 Out of Step (78) ............................... 158
4.4.14 Overfrequency and Underfrequency (81) .......... 161
4.4.15 Lockout Relay (86) ............................. 165
4.4.16 Generator Differential (87) .................... 166
4.5 Bibliography .......................................... 166
5 Electrical Apparatus Calculations .......................... 167
5.1 Buses ................................................. 167
5.2 Cable ................................................. 168
5.2.1 Withstand Seconds .............................. 168
5.2.2 Fusion Seconds ................................. 168
5.2.3 Line Loss ...................................... 170
5.3 Switchgear Circuit Breakers ........................... 170
5.3.1 Alternating Current (AC) Hi-Pot Testing ........ 170
5.3.2 Circuit Breaker Duty ........................... 172
5.4 Generators ............................................ 174
5.4.1 Acceptance Direct Current (DC) Hi-Pot .......... 174
5.4.2 Routine DC Hi-Pot .............................. 175
5.4.3 Temperatures ................................... 176
5.4.4 X/R Ratio ...................................... 178
5.5 Metering .............................................. 179
5.5.1 Theory ......................................... 179
5.5.2 Watt Demand .................................... 180
5.5.3 Watts .......................................... 181
5.6 Motors ................................................ 181
5.6.1 Acceptance DC Hi-Pot ........................... 181
5.6.2 Routine DC Hi-Pot .............................. 183
5.6.3 Locked Rotor Amps .............................. 183
5.6.4 Unbalanced Voltages ............................ 184
5.6.5 X/R Ratio ...................................... 184
5.6.6 Switching Transients ........................... 185
5.6.7 Reliability .................................... 187
5.6.8 Voltage Drop ................................... 188
5.7 Transformers .......................................... 188
5.7.1 Current Transformer Burden ..................... 188
5.7.2 Power Transformer Losses ....................... 190
5.7.3 Power Transformer X/R Ratio .................... 192
5.8 Bibliography .......................................... 192
6 Electrical Operating Guidelines ............................ 195
6.1 Operation of Large Generators ......................... 195
6.1.1 Purpose ........................................ 195
6.1.2 Startup Operation .............................. 196
6.1.3 Shutdown Operation ............................. 197
6.1.4 On-Line Operation .............................. 197
6.1.5 System Separation .............................. 198
6.1.6 Field Grounds .................................. 199
6.1.7 Voltage Regulators ............................. 200
6.1.8 Moisture Intrusion ............................. 200
6.1.9 Routine Operator Inspections ................... 201
6.1.10 Generator Protection ........................... 202
6.1.10.1 Differential (87) ..................... 202
6.1.10.2 Stator Ground (64) or (59G) ........... 202
6.1.10.3 Bus Ground Detectors (64B) or (59BG) .. 203
6.1.10.4 Loss of Excitation (40) ............... 204
6.1.10.5 Overexcitation (24) ................... 204
6.1.10.6 Reverse Power (32) .................... 205
6.1.10.7 Negative Phase Sequence (46) .......... 205
6.1.10.8 Backup Impedance (21) or Voltage
Restraint Overcurrent (51V) ........... 206
6.1.10.9 Out of Step (78) ..................... 207
6.1.10.10 Overfrequency and Underfrequency
(81) ................................. 207
6.1.10.11 Sync Check (25) ...................... 208
6.1.10.12 Inadvertent Energization (50/27) ..... 208
6.1.10.13 Pole Flashover (50NF) ................ 209
6.1.10.14 Main and Auxiliary Transformer
Differential (87) .................... 209
6.1.10.15 Feeder Differential (87) ............. 209
6.1.10.16 Overall Unit Differential (87) ....... 209
6.1.10.17 Auxiliary and Main Transformer
Sudden Pressure (63) ................. 210
6.1.10.18 Zone 1 Impedance (21) ................ 210
6.1.10.19 Breaker Failure (50BF) ............... 211
6.1.10.20 Transformer Overcurrent (51) ......... 211
6.1.10.21 DC Low Voltage (27DC) ................ 211
6.1.10.22 DC High Voltage (59DC) ............... 211
6.2 Operation of Large Power Transformers ................. 212
6.2.1 Purpose ........................................ 212
6.2.2 Operator Inspections ........................... 212
6.2.3 Sudden Pressure Relays ......................... 213
6.2.4 Transformer Differential or Sudden Pressure
Relay Operations ............................... 213
6.2.5 Emergency Cooling and Loading .................. 214
6.2.6 Oil Pump Operation ............................. 214
6.3 Operation of Large Electric Motors .................... 215
6.3.1 Purpose ........................................ 215
6.3.2 Operator Inspections ........................... 215
6.3.3 Starting Duty .................................. 216
6.3.4 Heaters ........................................ 216
6.3.5 Protection ..................................... 216
6.3.5.1 Instantaneous Phase Overcurrent
Tripping .............................. 216
6.3.5.2 Time Phase Overcurrent Tripping ....... 217
6.3.5.3 Feeder Ground Tripping ................ 217
6.4 Operation of Auxiliary System Switchgear .............. 218
6.4.1 Purpose ........................................ 218
6.4.2 Operator Inspections ........................... 218
6.4.3 Protection ..................................... 219
6.4.3.1 Load Feeder Overcurrent Protection .... 219
6.4.3.2 Load Feeder Ground Protection ......... 219
6.4.3.3 Source and Tie Overcurrent
Protection ............................ 219
6.4.3.4 High Side Source Transformer
Overcurrent Protection ................ 220
6.4.3.5 Source and Tie Residual Ground
Protection ............................ 220
6.4.3.6 Source Transformer Neutral Ground
Protection ............................ 221
6.4.3.7 Alarm-Only Ground Schemes ............. 221
6.4.4 Switchgear Bus Transfers ....................... 222
6.4.4.1 Paralleling Two Sources ............... 222
6.4.4.2 Drop Pickup Transfers ................. 222
6.4.4.3 Automatic Bus Transfer Schemes ........ 223
6.6 Bibliography .......................................... 223
7 Electrical Maintenance Guidelines .......................... 225
7.1 Generator Electrical Maintenance ...................... 225
7.1.1 Purpose ........................................ 225
7.1.2 Routine On-Line Slip-Ring Brush-Rigging
Inspections .................................... 226
7.1.1 Inspection of Rotor Grounding Brushes and
Bearing Insulation ............................. 228
7.1.4 Routine Unit Outages ........................... 228
7.1.5 Overhauls ...................................... 229
7.1.6 Vibration ...................................... 231
7.2 Transformer Electrical Maintenance .................... 232
7.2.1 Purpose ........................................ 232
7.2.2 Inspections .................................... 232
7.2.3 Transformer Testing ............................ 233
7.2.4 Avoiding Pyrolitic Growth in Tap Changers ...... 234
7.2.5 Internal Inspection ............................ 235
7.2.6 Electrostatic Voltage Transfer ................. 235
7.2.7 Dissolved Gas Analysis (DGA) ................... 236
7.2.8 Dielectric Breakdown Test ...................... 237
7.2.9 Insulators and Bushings ........................ 237
7.2.10 Sudden-Pressure Relays ......................... 237
7.2.11 Spare Transformer Maintenance .................. 238
7.2.12 Phasing Test ................................... 238
7.3 Motor Electrical Maintenance .......................... 238
7.3.1 Purpose ........................................ 238
7.3.2 Electrical Protection .......................... 238
7.3.2.1 Instantaneous Phase Overcurrent
Tripping (50) ......................... 239
7.3.2.2 Time Phase Overcurrent Tripping (51) .. 240
7.3.2.3 Feeder Ground Tripping (51G) .......... 241
7.3.3 Testing ........................................ 241
7.3.4 Internal Inspections ........................... 242
7.3.5 On-Line and Off-Line Routine Inspections ....... 243
7.3.6 Motor Monitoring and Diagnostics ............... 244
7.4 Switchgear Circuit Breaker Maintenance ................ 244
7.4.1 Purpose ........................................ 244
7.4.2 General—Switchgear Circuit Breakers (200
Volts to l5kV) ................................. 245
7.4.3 Inspection and Testing Frequencies ............. 246
7.4.4 Mechanical Inspection .......................... 246
7.4.5 Electrical Testing ............................. 247
7.4.6 Operational Tests .............................. 250
7.4.7 Cubicle Inspection ............................. 250
7.4.8 Rack-In Inspection ............................. 250
7.4.9 Generator DC Field Breakers .................... 251
7.5 Insulation Testing of Electrical Apparatus ............ 251
7.5.1 Purpose ........................................ 251
7.5.2 Apparatus 440 Volts and Higher ................. 252
7.5.3 Normal Routine Maintenance ..................... 252
7.5.4 Avoiding a Forced Outage or Load Restriction ... 253
7.5.5 DC High Potential Testing ...................... 253
7.5.6 Generator and Motor Stator Winding Test
Values ......................................... 256
7.5.7 Generator Rotor Field Test Values .............. 256
7.5.8 Generator Neutral Buses or Cables .............. 257
7.5.9 Cable 5 kV and Higher .......................... 257
7.6 Bus and Motor Control Center (MCC) Maintenance ........ 257
7.6.1 Purpose ........................................ 257
7.6.2 Bus Inspections ................................ 258
7.6.3 Bus Testing .................................... 258
7.6.4 MCC Position Inspections ....................... 259
7.6.5 MCC Position Testing ........................... 259
7.7 Protective Relay Testing .............................. 259
7.7.1 Purpose ........................................ 259
7.7.2 General ........................................ 259
7.7.3 Testing Schedule (440 Volts to 765 kV) ......... 259
7.7.4 Relay Routine Tests ............................ 260
7.7.5 Primary Overall Test of Current Transformers
(CTs) .......................................... 260
7.7.6 Documentation .................................. 261
7.7.7 Multifunction Digital Relay Concerns ........... 261
7.8 Battery Inspection and Maintenance .................... 261
7.8.1 Purpose ........................................ 261
7.8.2 General ........................................ 262
7.8.3 Floating Charges ............................... 263
7.8.4 Inspection Schedules ........................... 263
7.8.5 Safety Precautions ............................. 265
7.8.6 Operation and Troubleshooting .................. 266
7.9 Personnel Safety Grounds .............................. 267
7.9.1 Purpose ........................................ 267
7.9.2 General ........................................ 267
7.9.3 Special Grounding Considerations ............... 268
7.9.4 Maintenance .................................... 270
7.9.5 Electrical Testing ............................. 270
7.10 Generator Automatic Voltage Regulators and Power
System Stabilizers .................................... 271
7.10.1 Purpose ........................................ 271
7.10.2 Automatic Voltage Regulators ................... 271
7.10.3 Power System Stabilizers ....................... 271
7.10.4 Certification Tests ............................ 272
7.10.5 Routine Tests .................................. 272
7.10.6 Generating Station Responsibilities ............ 273
7.10.7 Excitation Engineering Responsibilities ........ 273
7.11 Bibliography .......................................... 273
Index ......................................................... 275
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