Answer / sundar m

AVR is the Automatic Voltage Regulator which is used to keep
the alternator terminal voltage to be constant whenever
voltage drop occurs....by varying the excitation and the
power supplied to the alternator with turbine...If AVR fails
then the voltage level of the alternator fails to be
constant.so the machine will comes out of synchronism.....

Some protection systems are there...to trip the machine when
the AVR fails so dont think like intelligents....

Answer / guest

Total failure of the Alternator

Answer / 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

Answer / rakesh.a.d

When AVR fails,the excitation to the generator fails and the alternator acts as an induction generator taking reactive power from the grid

Answer / sheikh

AVR is Automatic voltage regulator. AVR is a vital part of Alternator if Avr has become failed than alternator should gone at shutdown on undervoltage or No volltage safety. its make clear that whenever your enginator reduce the Rpm by any other fault than alternator also going on undervoltage safety that time AVR cannot balanced the determined voltage or Set point voltage.

Answer / k.prakashchandra

Generally if there is failure of AVR , excitation will switch over manual mode .

Answer / k.prakashchandra

Further ,the ' loss of excitation relay ' should act to trip . If it does not and the prime mover is still working , then the gen will run as induction generator . It may disturb stability as the pf is very low .

Answer / kaizad

Generally big power plants have a feature by which the manual rehostate follow AVE. So when Ave trips there is no sudden variations in power and by manual actions can be taken to avoid generator transformer overfluxing by keeping V/for ratio constant

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