Class_29/10/2026

EV 605/ EE605

Class_29/10/2026

If supply voltage is halved at constant frequency, the starting torque becomes approximately

1: If supply voltage is halved at constant frequency, the starting torque becomes approximately

Twice

One-fourth

Half

Unchanged

At very low frequency, voltage boost is required mainly to compensate for

2: At very low frequency, voltage boost is required mainly to compensate for

Mechanical losses

Increased synchronous speed

Stator resistance voltage drop

Increased leakage reactance

Above base frequency, with voltage limited to its rated value, the air-gap flux is approximately

3: Above base frequency, with voltage limited to its rated value, the air-gap flux is approximately

Increases with frequency

Decreases as 1/f

Remains constant

Decreases as 1/f²

Increasing rotor resistance, with all other equivalent-circuit parameters fixed, makes the maximum torque:

4: Increasing rotor resistance, with all other equivalent-circuit parameters fixed, makes the maximum torque:

Increase

Become zero

Remain unchanged

Decrease

An induction machine operating above synchronous speed in the direction of the rotating field has:

5: An induction machine operating above synchronous speed in the direction of the rotating field has:

Negative slip and generating operation

Positive slip and generating operation

Negative slip and motoring operation

Zero slip and motoring operation

The ratio of rotor copper loss to mechanical power developed is

6: The ratio of rotor copper loss to mechanical power developed is

(1 − s)/s

s

s/(1 − s)

1 − s

The rotor magnetic field rotates relative to the rotor at

7: The rotor magnetic field rotates relative to the rotor at

Rotor mechanical speed

Slip speed

Synchronous speed

Zero speed

At synchronous speed, the rotor-induced EMF is

8: At synchronous speed, the rotor-induced EMF is

Maximum

Zero

Half its standstill value

Equal to the stator voltage

In normal motoring operation, which power is high?

9: In normal motoring operation, which power is high?

Shaft output power

Air-gap power

Active electrical input power

Mechanical power developed

A 4-pole motor operates at 50 Hz and 1440 rpm. Frequency is reduced to 40 Hz while slip frequency remains constant. The new rotor speed is

10: A 4-pole motor operates at 50 Hz and 1440 rpm. Frequency is reduced to 40 Hz while slip frequency remains constant. The new rotor speed is

1152 rpm

1380 rpm

1200 rpm

1140 rpm