Protection of industrial power systems: 2nd

Preface to the second edition Preface to the first edition Simple protection devices Direct-acting trip Thermal trip Time-limit fuses Thermal overload devices Oil dashpots Fuses Moulded-case circuit-breakers Relays Induction relays Typical applications Attracted-armature relays Typical applications Moving-coil relays Thermal relays Timing relays Design Static relays Current and voltage transformers for protection Current transformers Construction Design Burden Operation Open-circuited current transformer Short-time factor Accuracy limit factor Specification of current transformers ix xi 1 2 2 3 6 6 7 15 19 19 22 27 29 30 33 34 34 37 41 41 41 42 43 44 46 47 47 48 vi Contents Rated secondary current Secondary winding impedance Primary windings Application Effect of CT magnetising current on relay setting Residual connection Quadrature or air-gap current transformers Summation current transformer Voltage transformers Accuracy Protection Residual connection Capacitor voltage transformers Fault calculations Impedance Fault level Generators Cables Source impedance Motors Practical example Current distribution Earth faults Time-graded overcurrent protection Settings Time-multiplier setting Application Discrimination with fuses Typical calculation Earth-fault protection Directional protection Directional relays Very inverse characteristic Extremely inverse characteristic High multiples of setting Unit protection Relays Application Protection of a motor CT knee-point voltage Overall setting 49 49 50 50 51 52 52 52 52 53 54 54 55 56 56 56 62 66 69 69 69 77 78 81 82 83 86 90 91 95 96 97 98 99 100 102 105 106 109 110 110 Contents vii The residual connection Busbar protection Phase and earth-fault schemes Settings Current setting Duplicate-busbar protection Mesh-connected substation Biased differential protection Transformer protection Types of fault Differential protection Magnetising inrush Tap-changing Biased systems High-speed biased systems Earth-fault protection Protection of an earthed-star winding Protection of the delta winding Buchholz protection Overcurrent protection Instantaneous high-set overcurrent protection Overload protection Protection of a typical industrial installation Restricted earth-fault protection Balanced earth-fault protection Overcurrent protection Standby earth-fault protection Feeder protection Differential protection Factors affecting the design Practical systems Teed feeder differential protection Transformer-feeder protection Intertripping Auxiliary equipment Electronic relays Impedance protection Motor protection Abnormal conditions Overload protection Phase unbalance 111 112 117 118 120 122 122 122 126 126 127 128 129 131 131 132 134 136 136 138 138 139 139 141 143 143 146 148 148 149 154 157 158 160 161 163 163 167 170 170 171 viii Contents Stalling Insulation failure Settings Static relays Differential protection Loss of supply Synchronous motors 10 Generator protection Insulation failure Earthing by resistor Earthing by transformer Stator protection Earth-fault protection Rotor earth-fault protection Unsatisfactory operating conditions Overcurrent protection Overload Failure of prime mover Loss of field Overspeed Overvoltage Protection of generator/transformer units Unit transformers Parallel operation (public supply) 11 Control circuits Batteries Power factor correction 12 Testing Works tests Tests on site Commissioning tests CT magnetising characteristic curves Relay characteristic check Static relays Insulation tests Tripping circuit check Routine maintenance tests Test equipment Care of protection relays 172 172 175 178 178 179 181 183 183 183 184 184 185 186 188 189 191 191 192 192 193 193 196 196 197 200 201 207 207 208 208 212 216 222 222 223 223 223 224 Index 227