Multiple Choice Questions on Electrical Machines - 2

Important Multiple Choice Questions in Electrical Machines

1.       In a shaded pole induction motor, the rotor runs from the
A)     Shaded portion to the unshaded portion of the pole while the flux in the former leads that of the latter
B)      Shaded portion to the unshaded portion of the pole while the flux in the former lags that in the latter
C)      Unshaded portion to the shaded portion while the flux in the former leads that it in the latter
D)     Unshaded portion to the shaded portion  while the flux in the former lags that in the latter
2.       The torque of a reluctance motor can be effectively increased by
A)     Increasing reluctance of the magnetic circuit along the direct axis
B)      Decreasing the reluctance of the magnetic circuit along the quadrature axis
C)      Increasing the ratio of the quadrature axis reluctance to direct axis reluctance
D)     Decreasing the ratio of quadrature axis reluctance to direct axis reluctance
3.       The starting current of a three phase induction motor is 5 times the rated current, while the rated slip is 4%. The ratio of starting torque to full-load torque is
A)     0.6
B)      0.8
C)      1.0
D)     1.2
4.       A single-phase transformer when supplied from 220V, 50Hz has eddy current loss of 50W. if the transformer is connected to a voltage of 330V, 50Hz, the eddy current loss will be
A)     168.75W
B)      112.5W
C)      75W
D)     50W
5.       In case of auto transformer, which of the following statements are correct?
                                I.            An auto-transformer requires less copper as compared to a conventional 2-winding transformer of the same capacity
                              II.            An auto-transformer provides isolation between the primary and secondary windings
                            III.            An auto-transformer has less leakage reactance as compared to the conventional 2-winding transformer of same capacity
Select the correct answer using the codes given below
A)     1,2 and 3
B)      1 and 2
C)      1 and 3
D)     2 and 3
6.       Switched reluctance motor  means
A)     Salient pole synchronous motor without excitation winding
B)      A stepper motor with salient poles
C)      Synchronous motors with salient poles on stator and rotor
D)     A stepper motor with closed loop control and with rotor position sensor
7.       A DC series motor is accidentally connected to a single phase AC supply. The torque produced will be
A)     Of zero average value
B)      Oscillating
C)      Steady and unidirectional
D)     Pulsating and unidirectional
8.       The synchronous impedance method of finding the voltage regulation by a cylindrical rotor alternator is generally considered as
A)     A pessimistic method because saturation is not considered
B)      An optimistic method because saturation is not considered
C)      A fairly accurate method even if power factor is not taken into account while determining synchronous impedance
D)     A fairly accurate method when power factor is taken into account while determining synchronous impedance
9.       Generally the no-load losses of an electrical machine is represented in its equivalent circuit by
A)     Parallel resistance with a low value
B)      Series resistance with a low value
C)      Parallel resistance with a high value
D)     Series resistance with a high value
10.   The power factor of a synchronous motor
A)     Improves with increase in excitation and may even become leading at high excitations
B)      Decreases with increase in excitation
C)      Is independent of its excitation

D)     Increases with loading for a given excitation




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