A group of machines (wind turbines) connected with 33KV
feeder and each machines are having individual VCB. The 33KV
feeder connected with 110KV/33KV substation. The 33KV feeder
tripped by over current at Substation and fault recorded at
Substation as OC-R&Y phase. Same time the group of machines
VCB tripped by over voltage, the fault recorded voltage was
above 66KV by numerical Under/Over voltage relay. While grid
drop time, this much of voltage hike is possible?

Answer Posted / k.prakashchandra

The load throw-off may result in run-away speed being equal
to twice the normal speed ,hence the voltage may also become
twice. Over voltage relay should be set at not more than
120%.You can employ the AVR so that the voltage does not
increase with the speed.

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