Generator over Fluxing Relay (24G)
[FONT="]Generator over Fluxing Relay (24G)[/FONT]
-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.
[FONT="]Data for setting calculations[/FONT]
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.)
-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.
#-Link-Snipped-#
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.
[FONT="]Data for setting calculations[/FONT]
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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