120. When an alternator is supplying unity power factor load, the armature reaction will produce
A. distortion of the main field
B. magnetisation of the main field
C. demagnetisation of the main field
D. none of the above

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121. If the driving force of both the alternators running in parallel is changed, this will result in change in
A. generated voltage
B. frequency
C. back e.m.f.
D. all of the above

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122. In an alternator, when the load power factor is unity
A. the armature flux will be damagnetising
B. the armature flux will be cross magnetising
C. the armature flux will reduce to zero
D. the armature flux will have square wave form

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123. The Potier's triangle separates the
A. stator voltage and rotor voltage
B. field m.m.f. and armature m.m.f.
C. armature leakage reactance and armature reaction m.m.f.
D. iron losses and copper losses

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124. In an alternator zero power factor method is used to find the
A. synchronous impedance
B. efficiency
C. armature resistance
D. voltage regulation

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125. If the driving power from the primemover driving an alternator is lost but the alternator remains connected to the supply network and field supply is on, then the alternator will
A. behave as an induction motor but will rotate an opposite direction
B. behave as a synchronous motor and will rotate in the same direction
C. get burnt
D. none of the above

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126. In turbo-alternators, smooth cylindrical type rotors used have long axial length because
A. it gives smooth running of the rotor
B. it reduces windage loss
C. centrifugal force is reduced
D. number of armature conductors being less, they have to be necessarily long for generating the required voltage

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