Test

Which part of a three-phase induction motor is stationary?

• Rotor

• Stator

• Shaft

• Commutator

The rotating magnetic field in an induction motor is produced by:

• Rotor current

• DC excitation

• Stator currents

• External magnets

The rotor of an induction motor always rotates:

• At synchronous speed

• Faster than synchronous speed

• Slower than synchronous speed

• In reverse direction

Slip in an induction motor is defined as:

• Synchronous speed / Rotor speed

• Rotor speed / Synchronous speed

• (Ns - Nr) / Ns

• (Nr - Ns) / Nr

Synchronous speed of a 4-pole motor running at 50 Hz is:

• 750 RPM

• 1000 RPM

• 1500 RPM

• 3000RPM

Which type of rotor is used in a squirrel cage induction motor?

• Cylindrical rotor

• Slip ring rotor

• Laminated rotor

• Short-circuited rotor bars

The rotor frequency in a 3-phase induction motor is equal to:

• Supply frequency

• Slip × Supply frequency

• Rotor speed × Poles

• Constant

A slip ring induction motor is started with:

• Star-delta starter

• Rotor resistance starter

• DOL starter

• Auto-transformer

The torque developed in a 3-phase induction motor is proportional to:

• Rotor resistance

• Slip

• Square of rotor current

• All of the above

The power factor of an unloaded induction motor is:

• Unity

• Leading

• Lagging

• Zero