# Electrical Machine MCQ (Multiple Choice Questions)

Electrical Machine MCQ Set 1 – In this Set of MCQ, We have provided 25 Questions and answers of the Electrical Machine Subject.

Q1. The primary and secondary windings of a transformer are

Q2. At what power factor, the voltage regulation of a transformer can be zero ?

• Lagging power factor
• Unity power factor
• Zero power factor

Q3. In a three phase star – delta transformer, what is the angle difference between primary and secondary phase voltages?

• Delta side lags by -30°
• Star side lags by -30°
• star side leads by 30°
• Delta side leads by 30°

Ans:- Delta side leads by 30°

Q4. What will be the eddy current loss if the supply frequency of a transformer becomes double?

• Eight times
• Four times
• Doubled
• Remains same

Ans:- Remains same

Q5. The efficiency of a transformer is mainly dependent on

• core losses
• copper losses
• stray losses
• dielectric losses

Ans:- core losses

Q6. Stable operation of an induction motor

• between zero slip and unity slip
• between 0.5 slip and 0.95 slip
• between zero slip and slip corresponding to maximum torque
• between slip corresponding to maximum torque and unity slip

Ans:- between zero slip and slip corresponding to maximum torque

Q7. In a 3 – ÃŽÂ¦ induction motor, the maximum torque is

• varies as rotor resistance.
• varies as the square of rotor resistance.
• varies inversely as rotor resistance.
• independent rotor resistance.

Ans:- independent rotor resistance

Q8. A 3 – ÃŽÂ¦ induction motor usually operates on

• unity power factor.
• 0.8 lagging power factor.
• 0.6 lagging power factor.

Ans:- 0.8 lagging power factor.

Q9. In an induction motor 5 % change in supply voltage, will cause rotor torque variation of

• 2.5 %.
• 5 %.
• 10 %.
• 50 %.

Ans:- 10 %.

Q10 A smaller air gap in a polyphase induction motor helps to

• reduce the chance of cogging.
• reduce the magnetizing current.
• increase the starting torque.
• reduce the chance of crawling.

Ans:- reduce the magnetizing current.

Q11. Slip rings of an induction motors are made of

• carbon
• stainless steel
• aluminium
• phosphor bronze

Ans:- phosphor bronze

Q12. Which type of bearing is provided in small induction motors to support the rotor shaft?

• Ball bearings.
• Bush bearings.
• Cast iron bearings.
• None of the above.

Ans:- Ball bearings

Q13. The rotor slots are slightly skewed in squirrel cage induction motor to

• economize on the copper to be used.
• provide ease of fabrication.
• reduce magnetic hum and locking tendency of rotor.
• increase of the strength of rotor bars.

Ans:- reduce magnetic hum and locking tendency of rotor

Q14. The induction motor shaft is made of

• mild steel
• cast iron.
• aluminium.
• stainless steel.

Ans:- mild steel

Q15. The shaft of induction motor may be unbalanced due to

• uneven air gap
• poor lubrication
• overheating of winding

Ans:- uneven air gap

Q16. Motors for fans and pumps are selected in the rpm range

• 375 to 500.
• 500 to 720.
• 720 to 920.
• 1440 to 2880.

Ans:- 1440 to 2880

Q17. Induction motors provided with open slots have

• more breakdown torque.
• less breakdown torque.
• higher efficiency.

Ans:- more breakdown torque.

Q18. The frame of an induction motor is made of

• closed grained cast iron.
• silicon steel.
• stainless steel.
• aluminium.

Ans:- closed grained cast iron

Q19. Use of fractional pitch winding

• make it stiffer.
• results in reduced leakage reactance.
• results in reduced axial length of the machine.
• all of the above

Ans:- all of the above

Q20. The rotor winding for a 3-phase slip-ring induction motor having delta-connected stator must be connected in

• delta.
• star.
• delta or star according to need.
• none of the above.

Ans:- star

Q21. The squirrel cage induction motors are provided with blades in order to

• eliminate noise.
• balance the rotor dynamically.
• facilitate cooling of rotor.
• none of these.

Ans:- facilitate cooling of rotor

Q22. Induction motors normally use cast aluminium rotor because aluminium is

• cheaper in cost.
• lighter in weight.
• of low resistivity.
• easy to cast owing to its low melting point and is easily available.

Ans:- easy to cast owing to its low melting point and is easily available

Q23. The shaft of induction motor should be

• stiff.
• hollow.
• flexible.
• any of these.

Ans:- stiff

Q24. Pole changing methods are suitable only for ___________ type induction motor.

• wound.
• cage.
• linear.
• none of these.

Ans:- cage

Q25. _____________ types of induction motor are widely used.

• Slip ring IM.
• Squirrel cage IM.
• Single phase IM.
• Three phase IM.

Ans:- Squirrel cage IM

Electrical Machine MCQ Set 1 – In this Set of MCQ, We have provided 25 Questions and answers of the Electrical Machine Subject.

See More:-

Power Electronics MCQs 1

Open and Closed Circuits MCQ