121. The windings for an alternator are
slots, four poles, span 1 to 8
II. 72 slots, six poles, span 1 to 10
III. 96 slots, six poles, span 1 to 12.
windings having pitch factors of more than 0.9 are
I and II only
(B) II and III only
I and II only
(D) I, II and III.
122 to 124 refer to data given below:
A 500 kVA ,2300 volt three phase
star connected alternator has a full load armature-resistance drop per phase of
50 volts and a combined armature reactance plus armature-reaction drop of 500
volts per phase
percent regulation of the alternator at unity power factor is
percent regulation of the alternator at 0.866 power factor lagging is
percent regulation of the alternator at 0.8 power factor leading is
(C) – 26.4
(D) – 13.2.
imaginary or fictitious part of synchronous reactance takes care of
of the above.
an alternator, the use of short pitch coils of 160° will indicate the absence
(B) fifth harmonic
(C) seventh harmonic
(D) ninth harmonic.
a generator designed for operation at 60 Hz is operated at 50 Hz
operating voltage must be derated to (50/60)
of its original value
operating voltage must be derated to (50/60)2 of its original value
kVA rating can be upgraded to (60/50) of the
the generator will not take any load.
of generator’s winding
(B) reduces power factor
life of the machine
not have any significant effect.
shaft of 500 MW alternator is supported in
(A) ball bearings
(B) roller bearings
(C) needle bearings
voltage of field system for an alternator is usually
than 200 V
200 V and 440 V
(C) 400 V
(D) more than 1 kV.
131. Maximum electric power output of a
synchronous generator is
(A) Xs / VtEf
(B) V2t / Xs
(C) E2f / Xs
(D) VtEf / Xs
electrical angle between the field axis and axis of armature reaction of a
loaded synchronous generator with armature current lagging behind the
excitation emf by ψ is
ψ + 90
(C) 90 – ψ
(D) ψ + 180.
synchronous generators G1and G2 are
equally sharing the KVAR of the load while operating in parallel. Keeping the
terminal voltage fixed in order to shift part of the KVAR load from G2 to G1
The field current of G1 is lowered
field current of G2 is raised
field current of G1 is raised and of G2 lowered
field current of G1 is lowered and of G2 is raised.
synchronous generator is operating with excitation adjusted for unity power
factor current at constant load. When on increasing the excitation the power
(A) will lag
(C) will become zero
(D) none of the above.
changing the speed of an alternator from 4000 rpm to 2000 rpm, the generated
emf phase will become