MCQ type questions
Sub: Induction, Synchronous and Special Electrical Machines
Topic: MCQ type question-
answers.
By Palash Das
Lecturer in Electrical Engineering; Bundwan Polytechnic.
1.In synchronous machine, poles are made up of thick steel laminations. In salient pole type rotor
a) Poles are projected out from the surface of the rotor
b) The unslotted portions of the cylinder acts itself as a poles
c) both a) and b)
d) None of these
Ans: a
2. The diameter and axial length of rotors of smooth
cylindrical type rotors are
a.Small diameter,
small axial length
b. Large diameter, large axial length
c. Large diameter, small axial length
d. Small diameter, large axial length
Ans: d
Note: Reverse in Salient pole
type rotor machine.
3.For high speed alternators or turbo alternators, which
type of rotor is generally used?
a. Salient pole type
b. Projected pole type
c. Smooth cylindrical type
d. Both (a) & (b)
Ans: c
Note: For low or medium type of
alternators Salient pole type rotor used
4. The phasor addition of stator and rotor mmfs is possible
in a smooth cylindrical synchronous generator because
a. Mmfs of stator and rotor are stationary with respect to
each other
b. Mmf of stator is stationary and that of rotor is rotating
c. Mmf of stator is rotating and that of rotor is stationary
d. None of these
Ans: a
5. The prime mover used in cylindrical rotor type machine is
a) Water turbine
b) I. C. Engines
c) both (a) and (b)
d) Steam turbine
Ans:d
Note:For projected type or Salient pole
type rotor alternators water turbine may be used as a prime moved.
6. In the brushless excitation system of synchronous
generator, the feedback of output voltage of alternator is taken and given to
the
a. Rotating armature a.c. excitor
b. Diode rectifier
c. Main alternator field
d. Magnetic amplifier
Ans: d.
7. During the one complete revolution of the conductor in a
4 pole synchronous generator, induced emf will experience
a. Two times maxima and two times zero
b. Two times maxima and four times zero
c. Eight times maxima and eight times zero
d. Four times maxima and four times zero
Ans: d
8. In a synchronous generator, one pole is responsible for
a. 90 degree electrical of induced emf
b. 180 degree electrical of induced emf
c. 360 degree electrical of induced emf
d. 720 degree electrical of induced emf
Ans: b.
9. Graph of armature current drawn by synchronous motor is
against field current is plotted then the resulted graph is known as
a. V-curves
b. Inverted V-curves
c. Both (a) & (b)
d. None of the above
Ans: a
10. The plot of power factor against field current in a synchronous motor is known as
a) V- curve
b) Inverted V - curve
c) Z - curve
d) None of these
Ans: b
11. The value of load angle δ and the internal machine angle
∅ for maximum power developed in synchronous motor is equal to
a. 0°electrical, 0° electrical
b. 0° electrical, 90° electrical
c. 90° electrical, 0° electrical
d. 90° electrical, 90° electrical
Ans: d
12.Oscillations of the rotor about its new equilibrium
position, due to sudden application or removal of load in synchronous motor is
called
a. Hunting
b. Galloping
c. Swinging
d. Both (a) and (c)
Ans: d
13.Hunting in a synchronous motor results in
a. Loss of synchronism
b. Mechanical and electrical stresses on motor
c. Large current drawn by motor
d. All of the above
Ans: d
14.In a synchronous motor, the phenomenon of hunting caused
by the sudden application or removal of load is prevented by
a. Using damper winding
b. Using a capacitor
c. Using an inductor
d. All of the above
Ans: a
15.An over excited synchronous motor operating on no load
condition is called as
a. Synchronous capacitor
b. Synchronous condensor
c. Hunting
d. Both (a) and (b)
Ans: d
16.The synchronous motor as a synchronous condenser is used
to
a. Improve power factor
b. Reduce hunting
c. Both (a) and (b)
d. None of the above
Ans: a.
17. The starting torque of an induction motor is maximum
when
a) Rotor resistance equals rotor reactance
b) Rotor resistance is twice the rotor reactance
c) Rotor resistance is half the rotor reactance
d) Rotor resistance is R2 times the rotor reactance
Ans: a
18. The synchronous speed of an induction motor is defined
as
a) Natural speed at which a magnetic field rotates
b) The speed of a synchronous motor
c) The speed of an induction motor at no load
d) None of these
Ans: a
19. The emf induced in the rotor of an induction motor is
proportional to
a) Voltage applied to stator
b) Relative velocity between flux and rotor conductors
c) Both (a) and (b) above
d) Slip
Ans: c
20. Starters are used in induction motor because
a) Its starting torque is high
b) It is run against heavy load
c) It can not run in reverse direction
d) Its starting current is five times or more than its rated
current
Ans: d
21.In an induction motor, rotor runs at a speed
a) Equal to the speed of stator field
b) Lower than the speed of stator field
c) Higher than the speed of stator field
d) Having no relation with the speed of stator field
Ans: b
22.In an induction motor, rotor slots are usually not quite
parallel to the shaft but are given a slight skew
a) To reduce the magnetic hum
b) To reduce the locking tendency of the rotor
c) Both (a) and (b) above
d) To increase the speed of the motor
Ans: c
23. In
an induction motor, the rotor input is 600 W and slip is 4%. The rotor copper
loss is
a) 700w
b)625w
c) 600w
d) 24 w
Ans:
Note: (i) The rotor input power Pir=Pg,
rotor copper loss Pc, gross mechanical power developed Pmd and slip has
below-mentioned relation.Pg : Pcu : Pmd = 1 : s : (1-s)
(ii) Pcu= sPg
24. The slip
frequency of an induction motor is
a) The frequency of rotor currents
b) The frequency of stator currents
c) Difference of the frequencies of the stator and rotor
currents
d) Sum of the frequencies of the stator and rotor currents
Ans: a
25. Advantage of slip ring induction motor over squirrel
cage induction motor is
a) Suitability of high speeds
b) Higher efficiency
c) Higher power factor
d) That it can be started using factor resistance
Ans:d
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