# Power Electronic Controlled Drives 5

Electrical Engineering MCQ Question Papers: Campus Placement

Subject: Power Electronic Controlled Drives 5

Part 5: List for questions and answers of Power Electronic Controlled Drives

Q1. Rotor resistance speed control is used in

a) Squirrel cage induction motor

b) Slip ring induction motor

c) Dc shunt motor

d) Synchronous motor

Q2. For satisfactory performance of 3-phase 480V, 60 Hz induction motor, the supply voltage at 50 Hz should be equal to

a) 480V

b) 400V

c) 420V

d) 350V

Q3. In a 3-phase induction motor, if the supply voltage and frequency are reduced by the same ratio, then slip at which maximum torque occurs is

a) More and maximum torque remains constant

b) More and maximum torque decreases

c) Less and maximum torque decreases

d) Less and maximum torque increases

Q4. To control the speed of an induction motor, the supply frequency is reduced by 10%. For the same magnetizing current to remain constant, the supply voltage must be

a) Reduced by 10%

b) Reduced by 20%

c) Increased by 10%

d) Increased by 20%

Q5. In V/f speed control of 3-phase induction motor, with increase in frequency, the slip at which maximum torque occurs

a) Increase

b) Decrease

c) Either of these

d) None of the above

Q6. In star-delta starting of squirrel cage induction motor compared to DOL starting the starting current and torque are

a) 1/root of 3, 1/3

b) 1/3, 1/3

c) 1/root of 3, 1/root of 3

d) 1/3, 1/root of 3

Q7. As compared to DOL starting, a cage induction motor with star-delta starting shall have

a) More starting torque

b) More starting time

c) Reduced starting current

d) Smoother acceleration

Q8. An induction motor has synchronous speed of 1500 rpm. What will be the slip when it is running on a speed of 1450 rpm?

a) +3.33%

b) -3.33%

c) +3%

d) -3%

Q9. For the purpose of starting an induction motor, star/delta switch is an equivalent to auto transformer of ratio

a) 33.3%

b) 66.3%

c) 50%

d) 57.7%

Q10. A 4 pole, 3-phase induction motor is running at 4% slip at full load. If the speed of the motor is 720 rpm, the supply frequency is

a) 50 Hz

b) 60 Hz

c) 25 Hz

d) 40 HZ

Q11. A voltmeter gives 120 oscillations per minute when connected to the rotor of an induction motor. The frequency is 50Hz. The slip of the motor is

a) 2%

b) 5%

c) 4%

d) 25%

Q12. An induction motor is, in general analogous to

a) Two winding transformer with secondary short circuited

b) Two winding transformer with secondary open circuited

c) Auto transformer

d) None of the above

Q13. A 3-phase slip ring induction motor is wound for 4 poles on stator and 6 poles on the rotor. When 3-phase balanced voltage source at 50 Hz is applied, it will run at

a) 1500 rpm

b) 1000 rpm

c) Zero speed

d) 750rpm

Q14. An induction motor has a rotor resistance of 0.002 ohm / phase. If the resistance is increased to 0.004 ohm / phase then the maximum torque will

a) Reduced to half

b) Increase by 100%

c) Increase by 200%

d) Remain unaltered

Q15. The power factor of squirrel cage induction motor is

a) Low at light loads only

b) Low at heavy loads only

c) Both A and B

d) Low at rated load only

Q16. Cogging of induction motor occurs at

a) High voltage and when stator and rotor poles are equal

b) Low voltage and when stator and rotor poles are equal

c) High voltage and when stator and rotor poles are not equal

d) Low voltage and when stator and rotor poles are not equal

Q17. Cogging and crawling are phenomena associated with

a) Cage induction machines and they are essentially the same

b) The former during starting and the latter at a fraction of its rated speed

c) The former at a fraction of its rate speed and the latter during starting

d) Any of the above

Q18. Cogging in induction motor occurs when

a) Number of stator teeth – number of rotor teeth = odd number

b) Number of stator teeth – number of rotor teeth = even number

c) Number of stator teeth – number of rotor teeth = 0

d) Number of stator teeth – number of rotor teeth = negative number

Q19. A 4 pole 50 Hz induction motor is running at 1470 rpm. Find the speed of stator magnetic field with respect to rotor?

a) 1470 rpm

b) 1500 rpm

c) 30 rpm

d) zero

Q20. No load test of 3-phase induction motor gives which of the following?

a) Constant loss

b) Variable loss

c) Both A and B

d) None of the above

Part 5: List for questions and answers of Power Electronic Controlled Drives