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# Quiz: Electrical Engineering 15 May 2021

Quiz: Electrical Engineering
Exam: DFCCIL
Topic: 3-Phase induction motor

Each question carries 1 mark.
Negative marking: 1/4 mark
Time: 10 Minute

Q1. To obtain greater efficiency, the slip of an induction motor should be………………
(a) 1
(b) Low
(c) High
(d) Very high

Q2. The direction of rotation of field in a 3-phase induction motor depends on the…
(a) Supply voltage
(b) Supply frequency
(c) Number of poles
(d) Phase sequence of supply voltage

Q3. If the slip of an induction motor is 0.25 and the synchronous speed is 600 rpm, the motor speed in rpm would be:
(a) 125
(b) 750
(c) 450
(d) 900

Q4. A 3-phase induction motor is running at 4 % slip. If the input to the rotor is 1000 W, then the mechanical power developed by the motor will be…………
(a) 0.96 W
(b) 96 W
(c) 960 W
(d) 9,600 W

Q5. When the rotor of three phase induction motor is blocked then the slip is
(a) 1
(b) 0
(c) 0.5
(d) 0.1

Q6. A 3-phase slip-ring induction motor is fed from the rotor side with stator winding short circuited. The frequency of the currents in the short-circuited stator is
(a) slip frequency
(b) supply frequency
(c) frequency corresponding to rotor speed
(d) zero

Q7. In an induction motor, what is the ratio of rotor copper loss and rotor input?
(a) 1/s
(b) s
(c)(1-s)
(d)s/(1-s)

Q8. For an induction motor, operating at slip s, the ratio of gross power output to air gap power is equal to
(a) (1-s)^2
(b) (1-s)
(c) √(1-s)
(d) (1-√s)

Q9. The synchronous speed for the 7^th space harmonic mmf wave of a 3-phase, 8 pole, 50 Hz induction machine is
(a) 5250 rpm in forward direction
(b) 5250 rpm in reverse direction
(c) 107.14 rpm in forward direction
(d) 107.14 rpm in reverse direction

Q10. The starting torque of a wound rotor induction motor can be increased by adding:
(a) External inductance to the rotor circuit
(b) External capacitance to the rotor circuit
(c) A combination of inductance and capacitance to the rotor circuit
(d) External resistance to the rotor circuit

SOLUTIONS

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