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| Generator over Fluxing Relay (24G) Posted: 01 Jan 2011 11:06 AM PST Generator over Fluxing Relay (24G) -The relay measures the ratio of voltage to frequency (V/Hz) as this ratio is proportional to the flux-density level of the electromagnetic machine. -Over Fluxing (Over Excitation) may be occur when a generator is on an isolated operation with the AVR in service and the generator speed decreasing from the synchronous speed. -Over Fluxing may also be occurring when the utility system frequency decreases to a low value by any reason.  There are two sets of the V/Hz relays are provided for Generator Protection:- A) Relay 24G (#2) for alarm A definite time element #2 of the relay will be used to provide an alarm. B) Relay 24G (#1 & INV) for trip Operation of the relay 24G will trip the switchyard breaker. An inverse time element of the relay will be used to provide a trip contact and a definite time element #1 is also used to further shape the protection curves. Data for setting calculations Short-time V/Hz withstand level at full load -----120% Continuous V/Hz withstand level at full load-----105% AVR V/Hz limiter setting -----------------------------105% Setting of generator V/Hz alarm relay 24G (#2) 1)V/Hz alarm setting Setting < continuous V/Hz withstand level at full load = 105 % 2)V/Hz alarm delay Setting = 30 cycles (0.6 Sec.) Setting of generator V/Hz alarm relay 24G (INV) 1) V/Hz trip setting for inverse time element Setting = 107 % 2) V/Hz Reset rate for inverse time element Reset rate = Practical recommendation is minimum setpoint of the relay Setting = 1 Sec. NOTE!! "If the generator is synchronized immediately after tripping by V/Hz relay operation, the generator will be damaged under V/Hz condition before limitation value. " Setting of generator V/Hz alarm relay 24G (#1) 1)V/Hz alarm setting Setting < short V/Hz withstand level at full load = 120 % 2)V/Hz alarm delay Setting = 50 cycles (1 Sec.) |
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