Generator Underexcitation Relaying

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How bad is it to have 40 elements with 0.5-0.6 second tripping times for large units? How quickly does tripping need to happen during an under excitation event to avoid damaging the unit?

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If you can't explain it to a six year old, you don't understand it yourself.

 

[RRaghunath]

0.6s delay is no issue.
The delay could even be 2s to avoid unnecessary trip of generator on '40' during a grid fault condition.
It is also a practice to wire under excitation coupled with under voltage for instantaneous trip.

Rompicherla Raghunath