Single Phase Motor Questions Answers

61. Single phase induction motor built with a variable air gap and without dc excitation is called the ……… motor.

(a) reluctance
(b) hysteresis
(c) repulsion
(d) split phase

62. A single phase reluctance motor

(a) has salient pole rotor structure and runs at sub-synchronous speed.
(b) has salient pole rotor structure and runs at super-synchronous speed.
(c) has salient pole rotor structure and runs at synchronous speed.
(d) has non-salient pole rotor structure and runs at synchronous speed. [A.M.I.E. Sec B. Elec. Machines Winter 1994]

63. Reluctance torque is the

(a) torque developed in a given synchronous motor as a function of field excitation and the sine of the torque angle.
(b) torque developed by salient pole synchronous or synchronous induction motors due to variations in air gap produced by armature reaction.
(c) torque developed by non-salient pole asynchronous motor.
(d) torque developed by none of the above. [A.M.I.E. Sec B. Elec. Machines Winter 1993; Summer 1997]

64. Reluctance motor

(a) is a self starting motor.
(b) runs at constant speed.
(c) needs no dc excitation for its rotor.
(d) starts as an induction motor and runs as a synchronous motor.
(e) all of the above.

65. In a reluctance motor, when the load increases to an extent that it cannot maintain synchronous speed, it will

(a) fall out of synchronism and come to rest.
(b) run as an induction motor.
(c) draw excessive armature current and burn out.
(d) become unstable.

66. The torque of a reluctance motor can be effectively increased by

(a) increasing reluctance of the magnetic circuit along the direct axis.
(b) decreasing reluctance of the magnetic circuit along the quadrature axis.
(c) increasing the ratio of quadrature axis reluctance to direct-axis reluctance.
(d) decreasing the ratio of quadrature axis reluctance to direct-axis reluctance. [U.P.S.C. I.E.S. E.E.-II, 2001]

67. Hysteresis motor is a

(a) synchronous induction motor.
(b) single phase induction motor.
(c) single phase synchronous motor without any salient pole and without dc excitation.
(d) single phase synchronous motor with salient poles and without dc excitation.

68. Hysteresis motor operates on the principle of

(a) hysteresis loss.
(b) eddy current loss.
(c) electromagnetic induction.
(d) magnetization of rotor.

69. The rotor of a hysteresis motor is made of magnetic material having area of hysteresis loop

(a) large.
(b) very small.
(c) medium.
(d) any of the above. [A.M.I.E. Sec B. Winter 2001]

70. Tile rotor of a hysteresis motor is built up of

(a) cast iron sheet.
(b) a group of specially hardened steel rings.
(c) thin silicon steel laminations.
(d) thin µ-metal laminations.

71. In an hysteresis motor, the rotor core must have

(a) retentivity.
(b) susceptibility.
(c) resistivity.
(d) none of these.

72. A hysteresis motor

(a) is a self starting motor.
(b) is a constant speed motor.
(c) does not need dc excitation.
(d) all of the above.

73. In a single phase hysteresis motor

(a) starting torque is caused by both eddy current and hysteresis while the running torque is caused by hysteresis.
(b) starting as well as running torques are caused by both eddy current and hysteresis.
(c) starting torque is caused by only eddy current while running torque is caused by only hysteresis.
(d) starting as well as running torques both are caused by only hysteresis.

74. A hysteresis motor

(a) has high starting torque due to its high rotor hysteresis loss.
(b) is extremely quite in operation due to absence of teeth and winding on rotor.
(c) accelerates from rest to full speed almost instantaneously.
(d) all of the above.

75. Hysteresis motors are used for Hi-Q record players because of their

(a) constant (synchronous) speed.
(b) extremely steady torque.
(c) insensitivity to supply voltage fluctuations.
(d) non-dependence on centrifugal switch requirement. [U.P.S.C. S. E.E.-II, 1998]

76. The main reason for using a hysteresis motor for high quality tape recorders and record players is that

(a) its speed is constant (synchronous).
(b) it develops extremely steady torque.
(c) it requires no centrifugal switch.
(d) its operation is not affected by mechanical vibrations. [U.P.S.C. LES. E.E.-II, 1995]

77. A fluctuating voltage supply is detrimental to a refrigerator motor but not to a ceiling fan, although both are single phase induction motors because, the refrigerator motor

(a) is made more robust than the fan motor.
(b) is subjected to short duty cycle but the fan motor is subjected to continuous duty.
(c) is enclosed in a sealed unit while the fan motor is open to the environment.
(d) load is constant, but the fan motor load is voltage dependent. [U.P.S.C. I.E.S. E.E.-11, 1993]

78. A ceiling fan uses

(a) capacitor motor.
(b) capacitor-start capacitor run motor.
(c) capacitor start motor.
(d) universal motor. [A.M.I.E. Sec B. Summer 2003]

79. Ceiling fan is

(a) three phase IM.
(b) single phase IM.
(c) single phase synchronous motor.
(d) none of these.

80. The electric motor generally used in household food mixers is

(a) universal motor.
(b) shaded pole motor.
(c) capacitor start motor.
(d) none of the above. [A.M.I.E. Sec B. Winter 2001]