GATE EE 2006 | Induction Machines Question 45 | Electrical Machines

GATE EE 2006

MCQ (Single Correct Answer)

-0.6

A $$3$$ phase, $$4$$ pole, $$400$$ $$V,$$ $$50$$ $$Hz,$$ star connected induction motor has following circuit parameters $${r_1} = 1.0\Omega ,\,{r_2} = 0.5\Omega ,$$ $${\mkern 1mu} {\mkern 1mu} {\mkern 1mu} {x_1} = x{'_2} = 1.2\Omega ,{\mkern 1mu} {x_m} = 35\Omega $$
The starting torque when the motor is started direct-on-line is (use approximate equivalent circuit model)

$$63.6$$ $$Nm$$

$$74.3$$ $$Nm$$

$$190.8$$ $$Nm$$

$$222.9$$ $$Nm$$

GATE EE 2005

MCQ (Single Correct Answer)

-0.6

Assertion [a]: Under V/f control of induction motor, the maximum value of the developed torque remains constant over a wide range of speed in the subsynchronous region.

Reason [r]: The magnetic flux is maintained almost constant at the rated value by keeping the ratio V/f constant over the considered speed range.

Both [a] and [r] are true and [r] is the correct reason for [a]

Both [a] and [r] are true but [r] is not the correct reason for [a]

Both [a] and [r] are false

[a] is true but [r] is false

GATE EE 2005

MCQ (Single Correct Answer)

-0.6

A three-phase cage induction motor is started by direct-on-line (DOL) switching at the rated voltage. If the starting current drawn is 6 times the full load current, and the full load slip is 4%, the ratio of the starting developed torque to the full load torque is approximately equal to

0.24

1.44

2.40

6.00

GATE EE 2005

MCQ (Single Correct Answer)

-0.6

Under no load condition, if the applied voltage to an induction motor is reduced from the rated voltage to half the rated value,

the speed decreases and the stator current increases

both the speed and the stator current decrease

the speed and the stator current remain practically constant

there is negligible change in the speed but the stator current decreases