1. A synchronous
motor which works on a leading power factor and does not drive a mechanical
load is called as
(A) static
condenser
(B) condenser
(C) synchronous
condenser
(D) none of the
above
Ans: C
2. A synchronous
motor develops maximum power when load angle is
(A) 45°
(B) 60°
(C) 90°
(D) 120°
3. In a synchronous
motor, the breakdown torque is
(A) directly
proportional to applied voltage
(B) directly
proportional to the square of the applied voltage
(C) inversely
proportional to applied voltage
(D) none of the
above
Ans: A
4. The maximum
torque which a synchronous motor will develop at rest for any angular position
of the rotor, at rated stator supply voltage and frequency, is known as
(A) locked-rotor
torque
(B) synchronous
torque
(C) pull up torque
(D) reluctance
torque
Ans: A
5. Exciters of
synchronous machines are
(A) d.c. shunt
machines
(B) d.c. series
machines
(C) d.c. compound
machines
(D) any of the
above
Ans: A
6. The coupling
angle or load angle of synchronous motor is defined as the angle between the
(A) rotor and
stator teeth
(B) rotor and the
stator poles of opposite polarity
(C) rotor and the
stator poles of the same polarity
(D) none of the
above
Ans: B
7. The maximum
constant load torque under which a synchronous motor will pull into synchronism
at rated rotor supply voltage and frequency is known as
(A) pull-up torque
(B) pull-in torque
(C) pull-out torque
(D) none of the
above
Ans: B
8. A synchronous
machine with low value of short-circuit ratio has
(A) lower stability
limit
(6) high stability
limit
(C) good speed
regulation
(D) good voltage
regulation
(e) none of the
above
Ans: A
9. The construction
of a synchronous motor resembles
(A) a series motor
(B) an induction
motor
(C) an alternator
(D) a rotary
converter
Ans: C
10. Which of the
following resistances can be measured by conducting insulation resistance test
on a synchronous motor ?
(A) Phase to phase
winding resistance
(B) Stator winding
to earthed frame
(C) Rotor winding
to earthed shaft
(D) All of the
above
Ans: D
11. Due to which of
the following reasons a synchronous motor fails to pull into synchronism after
applying D.C. field current ?
(A) High field
current
(B) Low short
circuit ratio
(C) High core
losses
(D) Low field
current
Ans: D
12. In a
synchronous motor, the maximum power developed depends on all of the following
except
(A) rotor
excitation
(B) maximum value
of coupling angle
(C) direction of
rotation
(D) supply voltage
Ans: C
13. If the
synchronous motor, properly synchronised to the supply is running on no load
and is having negligible loss
then
(A) the stator
current will be zero
(B) the stator
current will be very small
(C) the stator
current will be very high
(D) the back e.m.f.
will be more than the supply voltage
Ans: A
14 The armature
current of the synchronous motor
(A) has large
values for low excitation i niy
(B) has large
values for high excitation only
(C) has large
values for low and high excitation
(D) any of the
above
Ans: C
15. The maximum
power developed in a synchronous motor will depend on
(A) the rotor
excitation only
(B) the supply
voltage only
(C) the rotor
excitation and supply volt-age both
(D) the rotor
excitation, supply voltage and maximum value of coupling angle (90°)
Ans: D
16. A
rotary converter can also be run as a
(A) d.c. shunt
motor
(B) d.c. series
motor
(C) synchronous
motor
(D) induction motor
Ans: C
17. The maximum
speed variation in a 3-phase synchronous motor is
(A) 10 per cent
(B) 6 per cent
(C) 4 per cent
(D) zero
Ans: D
18. In a 3-phase
synchronous motor, the negative phase sequence exists when the motor is
(A) supplied with
unbalanced voltage
(B) under-loaded
(C) over-loaded
(D) none of the
above
Ans: A
19. The duration of
sudden snort-circuit test on a synchronous motor is usually about
(A) one hour
(B) one minute
(C) one second
(D) none of the
above
Ans: C
20. If the field
winding of an unloaded salient pole synchronous motor is open circuited, the
motor will
(A) stop
(B) run as
induction motor
(C) function as
static condenser
(D) burn with dense
smoke
Ans: A
