Surprise Quiz - I 20EI205

In squirrel cage induction motors, the rotor slots are usually given slight skew in order to _________.

• reduce windage losses

• reduce eddy currents

• reduce accumulation of dirt and dust

• reduce magnetic hum

In rotor resistance control of induction motor, the hardness of speed torque characteristics _________.

• increases

• decreases

• remains same

• zero

In a shaded pole motor, shading coils are using to ________.

• reduce winding losses

• reduce friction losses

• produce rotating magnetic field

• protect against sparking

The maximum power developed in a synchronous motor occurs at a coupling angle of _________.

• 30°

• 60°

• 90°

• 180°

In a three-phase induction motor, torque is produced due to the interaction of which two fields?

• Rotor magnetic field and the slip field

• Stator magnetic field and rotor magnetic field

• Armature current and stator magnetic field

• Commutator and rotor flux

A single-winding single -phase Induction motor has ________.

• Zero starting torque

• Low starting torque

• Starting torque equal to full load torque

• high starting torque

The range of slip s in 3-phase induction machine during motor mode of operation is

• -1 < s < 0

• 0 < s <1

• -2 < s < -1

• 1 < s < 2

The slip in an induction motor is defined as:

• The difference between synchronous speed and rotor speed

• The ratio of rotor speed to synchronous speed

• The product of rotor speed and synchronous speed

• The difference between stator current and rotor current

In a torque-slip characteristic of an induction motor, what happens to the torque as the slip increases beyond the full-load slip?

• Torque remains constant

• Torque decreases

• Torque increases linearly

• Torque increases exponentially

Synchronous motors are generally not self-starting because:

• They require DC supply

• Their starting torque is zero

• They cannot operate at low speeds

• They are not efficient