Electrical Machines
Dummy coils are used for

 reducing armature reaction.
 mechanical balancing.
All of these
 increasing efficiency.

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Electrical Machines
Which of the following is done in speed control of DC motor by field flux control?

 Any of above.
 Inserting an additional resistance in the field circuit.
 Inserting an additional resistance in the armature circuit.
 Inserting resistance to armature circuit and field circuit.

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Electrical Machines
Interpoles in a DC motor must be

 Series excited and should have the same polarity as that of the ahead main pole in the direction of rotation of armature.
 Shunt excited and should have the same polarity as that of the behind main pole in the direction of rotation of armature.
 Series excited and should have the same polarity as that of the behind main pole in the direction of rotation of armature.
 Shunt excited and should have the same polarity as that of the ahead main pole in the direction of rotation of armature.

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Electrical Machines
In a synchronous generator with constant steam input supplies power to an infinite bus at a lagging power factor. If the excitation is increased

 power angle decrease and power factor increase
 power angle increase and power factor decrease
 both power angle and power factor decrease
 both power angle and power factor increase

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