Failure of AVR means AVR will not deliver the excitation
voltaage to the exciter winding.Hance Excitor winding will
not be able to generate any excitor voltage.So there will
be no any field votage to rotor field winding and due to
this even if DG continious running but there will be no out
AVR-AUTOMATIC VOLTAGE REGULATOR. AS THE NAME IMPLIES IT IS
USED FOR THE REGULATION OF VOLTAGE & VOLTAGE BUILD UP
PURPOSES.IT CONSISTS OF (VOLTAGE SENSING UNIT,VOLTAGE BUILD
UP CKT,PULSE WIDTH MODULATION CKT,etc...,).OBVIOUSLY IF AVR
FAILS THERE WILL BE NO VOLTAGE.SO DG RUNS WITHOUT VOLTAGE
AND THERE WILL BE NO LOAD.
1. If the avr is not giving any output voltage ie DC to the
excitor then no voltage build up will be there.
2. If the avr is not changing the dc voltage as per load
demand then voltage variation will be observed.Which means
the automatic rerulation function of avr wrt load is not
working.Hence avr needs replacement.
it depends upon which type of avr is that .. if its an
static one than it will get tripped and no dc output and dg
set will not generate any voltage. but if avr having no
interlock with excitor than if avr fails than it will only
affect the regulation of voltage as excitation voltage is
already generating and being given to alternator so output
will be there but non-regulated