AC DRIVES

The starting torque of an indication motor is maximum when

• Rotor resistance equals rotor reactance

• Rotor resistance is twice the rotor reactance

• Rotor resistance is half the rotor reactance

• Rotor resistance is R2 times the rotor reactance

The emf induced in the rotor of an induction motor is proportional to

• Voltage applied to stator

• Relative velocity between flux and rotor conductors

• Both (a) and (b) above

• Slip

The field winding of a three phase synchronous machine is excited by

• Single-phase ac supply

• Three- phase ac supply

• Dc supply

• Supply obtained from an inverter

This starting method typically allows a motor to develop 150% of its rated ________ while the VFD is drawing less than 50% of its rated current from the mains in the low speed

• Torque

• Energy

• Force

• Angular momentum

Main advantage of an ac motor as compared to a DC motor is

• Large slip

• lower starting torque

• Higher efficiency

• Higher power factor

The starting torque of a squirrel-cage induction motor is

• Full-load torque

• Slightly more than full-load torque

• Low

• Negligible

A 50 Hz, 3-phase induction motor has a full load speed of 1440 r.p.m. The number of poles in the motor is

• 2 pole

• 4 pole

• 6 pole

• 8 pole

Which of the following motor has high starting torque?

• Slip ring Induction motor

• Squirrel cage Induction motor

No load test of 3-phase induction motor used to determine

• Variable loss

• Constant loss

• Eddy current loss only

• Hysteresis loss only

Introducing the external resistance increases

(i) speed (ii) output power (iii) starting torque

• (iii)

• (ii),(iii)

• (ii)

• (i), (ii), (iii)