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Electrical Engineering Objective Questions { Synchronous Motors }

141.  A synchronous motor is cheaper than 3-phase induction motor for
A. high speed, high output
B. high speed, low output
C. low speed, high output
D. none of the above
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142. Synchronous motors are generally used in applications requiring
A. infrequent starting
B. variable speed
C. sudden application of heavy loads
D. frequent stopping
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143. In a synchronous motor, the magnitude of stator back e.m.f. Eb depends on
A. speed of the rotor
B. load on the motor
C. both the speed and rotor flux
D. d.c. excitation only
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144. If load angle of a 4-pole synchronous motor is 80 (elect.), its value in mechanical degrees is
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145. When load on a synchronous motor running with normal excitation is increased, armature current drawn by it increases because
A. back e.m.f. Eb becomes less than the applied voltage V
B. power factor is decreased
C. net resultant voltage Er in armature is increased
D. motor speed is reduced
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146. A 18.-65 kW, 220 V, 50 Wz, 4-pole, Y-connected synchronous motor is running with a light load. The load angle is 4?(elect.) and back e.m.f. generated per phase in 110 V. If the armature resistance per phase is 0.10 and synchronous reactance / phase is 1.511, then resultant armture voltage/phase is
A. 5.4 V
B. 18.9 V
C. 72.4 V
D. 26.8 V
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147.  An over-excited synchronous motor running in parallel with induction motors can be used in improve the power factor of
A. supply line
B. transformer
C. generators
D. all of the above
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