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.

Electrical Machine MCQ

Q1. The primary and secondary windings of a transformer are

  • conductively linked
  • inductively linked
  • electrically linked
  • mechanically linked

Ans:- inductively linked

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

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

Ans:- Leading 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 – Φ 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 – Φ induction motor usually operates on  

  • unity power factor.  
  • 0.8 leading 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  
  • overload

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. 
  • leading power factor

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.

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