Electrical Machines
The speed of a cumulatively compound DC motor can be controlled by varying

 Armature voltage control.
 Shunt field resistance control.
 Armature resistance control.
 Any of above.

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Electrical Machines
Consider the following statements about commutating poles which are fitted on most large dc Shunt motors: 1. The commutating poles are placed in the geometric neutral plane and their number is usually Equal to the number of main poles 2. The winding on the commutating poles is connected in series with the shunt-field winding on the main poles 3. The polarity of the commutating pole must be that of the next pole further ahead 4. The commutating poles neutralize the reactance voltage produced in the coil undergoing Commutation. Of these statements,

 1, 2 and 3 are correct
 1, 2 and 4 are correct
 1 and 4 are correct
 2, 3 and 4 are correct

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Electrical Machines
An alternator is feeding an infinite busbar. Its prime mover is suddenly shutdown. The alternator will

 continue to work as alternator but the direction of rotation will reverse.
 continue to work as synchronous motor with same direction of rotation.
 come to stand still.
 start working as induction motor.

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