Handbook of Electrical Engineering

328 HANDBOOK OF ELECTRICAL ENGINEERING Figure 12.11 Protection devices for a three-winding transformer. The number of these prot ...

PROTECTIVE RELAY COORDINATION 329 generated by the production facility. Drilling rig DC systems are fed from a 600 V unearthed s ...

330 HANDBOOK OF ELECTRICAL ENGINEERING Very and extremely inverse relays are used in systems where the fault level downstream is ...

PROTECTIVE RELAY COORDINATION 331 Figure 12.12 Various standard inverse time characteristics of a time-dependent overcurrent rel ...

332 HANDBOOK OF ELECTRICAL ENGINEERING winding. Instantaneous protection is applied to respond to major three-phase faults at or ...

PROTECTIVE RELAY COORDINATION 333 cable, and to coordinate with the protective devices downstream e.g. an exceptionally large co ...

334 HANDBOOK OF ELECTRICAL ENGINEERING Figure 12.14 Protection devices for a high voltage feeder cables. 12.6 Busbar Protection ...

PROTECTIVE RELAY COORDINATION 335 to open the incomer and bus-section circuit breakers so that the fault does not develop and sp ...

336 HANDBOOK OF ELECTRICAL ENGINEERING 12.7 High Voltage Induction Motor Protection Most oil industry plants use high voltage in ...

PROTECTIVE RELAY COORDINATION 337 Figure 12.15 Protection devices for high voltage motors. 12.7.1 Overloading or thermal image A ...

338 HANDBOOK OF ELECTRICAL ENGINEERING Figure 12.16 Operating time of a motor thermal image relay. The motor is assumed to be ru ...

PROTECTIVE RELAY COORDINATION 339 When thetcand thethfunctions are plotted with log-log scales they exhibit slight curvature at ...

340 HANDBOOK OF ELECTRICAL ENGINEERING 12.7.4 Core balance earth fault Earth faults that occur within the stator windings will u ...

PROTECTIVE RELAY COORDINATION 341 Figure 12.18 Motor run-up, thermal and instantaneous relay curves. The cold and hot thermal im ...

342 HANDBOOK OF ELECTRICAL ENGINEERING may not present a problem to the motor but the driven machine could be damaged if it is a ...

PROTECTIVE RELAY COORDINATION 343 Note: For small motors, e.g. 22 kW and below, the earth loop impedance including the feeder ca ...

344 HANDBOOK OF ELECTRICAL ENGINEERING Figure 12.20 Thermal and instantaneous curves of a motor relay. Hot and cold characterist ...

PROTECTIVE RELAY COORDINATION 345 12.8.4 Core balance earth fault This function is occasionally required because the earth loop ...

346 HANDBOOK OF ELECTRICAL ENGINEERING 12.9.1 Time-delayed overcurrent A time-delayed overcurrent (51) relay would normally be u ...

PROTECTIVE RELAY COORDINATION 347 Table 12.1. The value of the exponent ‘a’ for different relay curves Type Range ofa Preferred ...