Starting of Polyphase Induction Motors – Part 2

Torque-slip characteristic of an induction motor is linear in the smaller slip values, because

If an emf at slip frequency is injected at an angle α with existing rotor induced emf, then

If a 3-phase induction motor is fed from the rotor short circuiting the stator terminals, frequency of the current flowing in the short-circuited stator is

I. Rotor resistance is dependent on the speed.
II. Core loss does not depend on the supply frequency and voltage.

For a 3-phase 4-pole induction motor has open circuited slip rings. The frequency across the slip rings is 75 Hz. Then we can conclude that the motor is run at a speed of
(i) 750rpm (ii) 1500rpm (iii) 2250rpm (iv) 3750 rpm

For 3-phase induction motor, as load increases from no load towards the full load,

For 3-phase induction motor, as load increases from no load towards the full load, torque _______ slip.

Choose from the below which can be obtained by the equivalent circuit of an electrical machine?

A 3-phase slip ring IM is has its copper bars replaced by the aluminium bars in the machine. With the above change,

As a 3-phase induction motor, as load increases from no load towards the full load,
A. power factor improves
B. torque increases
C. air gap flux falls steeply

The stator of a 3-phase, six pole induction motor’s stator is connected to 50 Hz supply while its rotor is fed from a 20 Hz supply.
The possible speeds at which the machine will run will be
(i) 1600rpm (ii) 600rpm (iii) 1400rpm (iv) 400 rpm

I. Leakage reactance is dependent on supply current.
II. Magnetizing reactance is dependent on the air gap flux.
Which of the following is correct?

Due to the line to ground fault, phase ‘a’ in the induction motor phase supply gets cut, then machine

A constant torque variable power drive of induction machine has

A 3-phase induction motor is fed at the stator at a frequency f. If the rotor speed is Nr and synchronous speed is Ns, then the absolute speed of the resultant flux in space is

A 3-phase slip ring IM is has its copper bars changed by the aluminium bars in the machine. With the above change,

A center ammeter connected to the rotor end circuit of a 6-pole,50 Hz, induction motor makes 45 complete oscillations in a minute.
Then the rotor speed and the speed of stator field w.r.t. rotor is

If one of the supply fuses blows off and gets open circuited, then for the connected induction machine continues to run with increased slip.