Answer Posted / jagan

When AVR fails a protection called Field Failure protection will come into picture and trip the generator.
When AVR trips the machine draws reactive power from grid n continue to run as Induction Generator but above synchronous speed which might damage the turbine.
It has 2 time delays
If Failure of field is associated with under voltage which might happen due to severe fault near the generator and AVR might trip not able to maintain the voltage, the generator is tripped instantaneously.
If the AVR fails and there is no U/V, a delay of 1-2 sec is incorporated hoping the AVR might restore. 
PROTECTION ENGINEER 11 YEARS EXP

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