Handbook of Electrical Engineering

FAULT CALCULATIONS AND STABILITY STUDIES 307 Stability studies will help to minimise these possibilities. When planning a stabil ...

308 HANDBOOK OF ELECTRICAL ENGINEERING Include typical transformers by their per-unit reactance. Neglect their resistance. Incl ...

FAULT CALCULATIONS AND STABILITY STUDIES 309 Francis Scheid,Theory and problems of numerical analysis. Schaum’s Outline Series. ...

12 Protective Relay Coordination 12.1 Introduction to Overcurrent Coordination Protective devices, usually relays or fuses, are ...

312 HANDBOOK OF ELECTRICAL ENGINEERING Figure 12.1 One-line diagram of an equivalent power system that has its own dedicated gen ...

PROTECTIVE RELAY COORDINATION 313 The large motors have long run-up times e.g. 10 to 20 seconds for high speed centrifugal gas ...

314 HANDBOOK OF ELECTRICAL ENGINEERING Reverse active power (32). Negative phase sequence (46). Stator earth fault current (51 ...

PROTECTIVE RELAY COORDINATION 315 a) The fault current supplied by the generator is initially high (approximately 5 to 8 times t ...

316 HANDBOOK OF ELECTRICAL ENGINEERING at the generator is used to measure the severity of the fault. The greater the fall in vo ...

PROTECTIVE RELAY COORDINATION 317 Figure 12.5 Definite time overcurrent relay with a two-stage characteristic. Figure 12.6 Inver ...

318 HANDBOOK OF ELECTRICAL ENGINEERING 12.2.2.4 Influence of the load characteristics Occasionally a power system may contain mo ...

PROTECTIVE RELAY COORDINATION 319 Figure 12.7 Effect of a large load variation on the response of overcurrent relays at the gene ...

320 HANDBOOK OF ELECTRICAL ENGINEERING Since the power from the prime-mover cannot be transmitted from the generator there will ...

PROTECTIVE RELAY COORDINATION 321 Conversion factor for referring the generator reactances to theCTandVTsecondary circuits:- Xse ...

322 HANDBOOK OF ELECTRICAL ENGINEERING power transfer into the generator being from other generators or utility sources in the n ...

PROTECTIVE RELAY COORDINATION 323 unearthed; but in such cases earthing of the power system is provided artificially at the busb ...

324 HANDBOOK OF ELECTRICAL ENGINEERING the current transformer to balance the ampere-turns across its windings. It is the normal ...

PROTECTIVE RELAY COORDINATION 325 is used. An undervoltage relay (27) is used to trip the generator if the voltage falls below a ...

326 HANDBOOK OF ELECTRICAL ENGINEERING In view of the need to continue operation it is possible to tolerate some relaxation in t ...

PROTECTIVE RELAY COORDINATION 327 Figure 12.9 Protection devices for a two-winding transformer with NER. Figure 12.10 Protection ...