## Electrical Machines The rotor speed of an induction motor is given by

Ns = 120f / p Ãƒâ€” ( 1 - s ).
None of these
Nr = 120f / p Ãƒâ€” (1-s).
Ns = 120f /p Ãƒâ€” ( 1 - r).

## Electrical Machines In a 3-phase induction motor, if the supply voltage and frequency are reduced by the same ratio, then slip at which maximum torque occurs is

less and maximum torque increases
more and maximum torque decreases
more and maximum torque remains constant
less and maximum torque decreases

375 rpm
3000 rpm
75 rpm
1500 rpm

## Electrical Machines The efficiency of a transformer is mainly dependent on

stray losses.
dielectric losses.
copper losses.
core losses.

## Electrical Machines Ward-Leonard control is basically a ___________ control method.

Field diverter control.
Field control.
Armature voltage control.
Armature resistance control.

## Electrical Machines A 3-φ alternator has negligible stator resistance. A short circuit test is conducted on this alternator. At a particular speed, a field current of If1 is required to drive the rated armature current. If the speed of the alternator is reduced to half, the field current required to maintain rated armature current

Would be equal to If1.
Cannot be predicted due to insufficient data.
Woud be equal to 2If1.
Would be equal to If1/2.