Generator over Fluxing Relay (24G
 

[LEFT]
[B][I][U][F**T=&quot]Generator over Fluxing Relay (24G)[/F**T][/U][/I][/B]
[B]

-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.[/B]
[B]-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.[/B]
[B]-Over Fluxing may also be occurring when the utility system frequency decreases to a low value by any reas**.[/B]


[URL="http://3.bp.blogspot.com/_CZnqYQLLQtc/TR936cGYLUI/AAAAAAAAAHk/fWe1cQjG6DI/s1600/Over_flux.JPG"][IMG]http://3.bp.blogspot.com/_CZnqYQLLQtc/TR936cGYLUI/AAAAAAAAAHk/fWe1cQjG6DI/s400/Over_flux.JPG[/IMG][/URL]



[B]There are two sets of the V/Hz relays are provided for Generator Protecti**:-[/B]
[U][F**T=Impact]

A) Relay 24G (#2) for alarm[/F**T][/U]
[B]A definite time element #2 of the relay will be used to provide an alarm.[/B]
[U][F**T=Impact]B) Relay 24G (#1 & INV) for trip[/F**T][/U]
[B]Operati** of the relay 24G will trip the switchyard breaker.[/B]
[B]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.[/B]

[B][U][F**T=&quot]Data for setting calculati**s[/F**T][/U][/B]
[B][I]Short-time V/Hz withstand level at full load -----120%[/I][/B]
[B][I]C**tinuous V/Hz withstand level at full load-----105%[/I][/B]
[B][I]AVR V/Hz limiter setting -----------------------------105%[/I][/B]


[U][F**T=Impact]

Setting of generator V/Hz alarm relay 24G (#2)[/F**T][/U]
[B][I][U]1)V/Hz alarm setting[/U][/I][/B]
[B]Setting < c**tinuous V/Hz withstand level at full load = 105 %[/B]
[B][I][U]2)V/Hz alarm delay[/U][/I][/B]
[B]Setting = 30 cycles (0.6 Sec.)[/B]

[U][F**T=Impact]


Setting of generator V/Hz alarm relay 24G (INV)[/F**T][/U]
[B][I][U]1) V/Hz trip setting for inverse time element[/U][/I][/B]
[B]Setting = 107 %[/B]
[B][I][U]2) V/Hz Reset rate for inverse time element[/U][/I][/B]
[B]Reset rate = Practical recommendati** is minimum setpoint of the relay [/B]
[B]Setting = 1 Sec.[/B]
[B] [/B]
[B]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. “ [/B]


[U][F**T=Impact]Setting of generator V/Hz alarm relay 24G (#1)[/F**T][/U]
[B][I][U]1)V/Hz alarm setting[/U][/I][/B]
[B]Setting < short V/Hz withstand level at full load = 120 %[/B]
[B][I][U]
[/U][/I][/B]
[B][I][U]2)V/Hz alarm delay[/U][/I][/B]
[B]Setting = 50 cycles (1 Sec.)[/B][/LEFT]

مشكور على المعلومات