Multiple Choice Questions on Electrical Machines -1

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Important Multiple Choice Questions in Electrical Machines


1.       In an electromechanical energy conversion device, the developed torque depends upon
A)     Stator field strength and torque angle
B)      Stator field and rotor field strengths
C)      Stator field and rotor field strengths and the torque angle
D)     Stator field strength only
2.       Consider the following statements:
The use of interpoles in dc machines is to counteract the
                                I.            Reactance voltage
                              II.            Demagnetizing effect of armature mmf in the commutating zone
                            III.            Cross-magnetizing effect of armature mmf in the commutating zone
Which of these statement(s) is/are correct?
A)     1 &2
B)      2&3
C)      1&3
D)     3 alone
3.       The current drawn by a 220V DC motor of armature resistance 0.5 ohm and back emf 200V is
A)     40A
B)      44A
C)      400A
D)     440A
4.       A DC shunt generator when driven without connecting field winding shows an open circuit terminal voltage of 12V. when field winding is connected and excited, the terminal voltage drops to zero because
A)     Field resistance is higher than critical resistance
B)      There is no residual magnetism in the field circuit
C)      The field winding is wrongly connected
D)     There is a fault in armature circuit
5.       The advantage of the double squirrel-cage induction motor over single cage rotor is that its
A)     Efficiency is higher
B)      Power factor is higher
C)      Slip is higher
D)     Starting current is lower
6.       An induction motor when started on load does not accelerate up to full speed but runs at 1/7 th of the rated speed. The motor is said to be
A)     Locking
B)      Plugging
C)      Crawling
D)     Cogging
7.       Synchronous condenser means
A.      A synchronous motor with capacitor connected across stator terminals to improve power factor
B.      A synchronous motor operating at full load with leading power factor
C.      An over-excited synchronous motor partially supplying mechanical load, and also improving power factor of the system to which it is connected
D.      An over-excited synchronous motor operating at no-load with leading power factor used in large power stations for improvement of power factor
8.       In cylindrical rotor synchronous machine, the phasor addition of stator and rotor mmfs is possible because
A)     Two mmfs are rotating in opposite direction
B)      Two mmfs are rotating in same direction at different speed
C)      Two mmfs are stationary with respect to each other
D)     One mmf is stationary and the other mmf is rotating
9.       The rotor power output of 3-phase induction motor is 15kW. The rotor copper losses at a slip of 4% will be
A)     600W
B)      625W
C)      650W
D)     700W
10.   Skewing of the rotor in a three-phase squirrel-cage induction motor reduces
A)     Noise, parasitic torque, starting torque and pullout torque
B)      Noise and parasitic torque, but increases starting torque and pull out torque
C)      Noise and pullout torque, but increases parasitic torque and starting torque

D)     Noise, parasitic torque and starting torque, but increases pullout torque

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