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Electrical Engineering Objective Questions { Alternators }

127. Large-diameter salient-pole rotors have short axial length mainly because
A. it occupies much less space
B. it reduces rotor weight
C. number of armature conductors held in the large circuimference rotor being very large, they need not be long
D. it save lot of copper in stator winding
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128.  At leading power factor, the armature flux in an alternator
A. distorts the rotor flux
B. aids the rotor flux
C. opposes the rotor flux
D. does not affect the rotor flux
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129. Three-phase alternators are invariably star-connected because
A. higher terminal voltage is obtained
B. less turns of wire are required
C. small conductors can be used
D. magnetic losses are the mainmum
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130. Which of the following conditions does not have to be met by alternators working in parallel?
A. Alternators must operate at the same frequency
B. Machines must have the same phase rotation
C. The terminal voltage of each machine must be the same
D. The machines must have equal kVA ratings
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131. The fictitious part of synchronous reactance takes care of
A. inductive reactance
B. armature reaction
C. voltage regulation
D. none of the above
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132. In an alternator the voltage of field system is usually
A. more than 1000 V
B. between 40 V and 600 V
C. less than 200 V
D. none of the above
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133. In an alternator, pitch factor is the ratio of the e.m.fs. of
A. full pitch winding to short pitch winding
B. short pitch coil to full pitch coil
C. distributed winding to full pitch winding
D. full pitch winding to concentrated winding
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