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Khaled Hamza · #1 01-01-2011, 07:05 PM

Generator over Fluxing Relay (24G)

-The relay measures the ratio of voltage to frequency (V/Hz) as this ratio is proporti**al to the flux-density level of the electromagnetic machine.
-Over Fluxing (Over Excitati**) may be occur when a Generator is ** an isolated operati** with the AVR in service and the generator speed decreasing from the synchr**ous speed.
-Over Fluxing may also be occurring when the utility system frequency decreases to a low value by any reas**.

There are two sets of the V/Hz relays are provided for Generator Protecti**:-

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
Operati** of the relay 24G will trip the switchyard breaker.
An inverse time element of the relay will be used to provide a trip c**tact and a definite time element #1 is also used to further shape the protecti** curves.

Data for setting calculati**s
Short-time V/Hz withstand level at full load -----120%
C**tinuous 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 < c**tinuous 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 recommendati** is minimum setpoint of the relay
Setting = 1 Sec.

NOTE!! “If the generator is synchr**ized immediately after tripping by V/Hz relay operati**, the generator will be damaged under V/Hz c**diti** before limitati** 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.)