Electrical Studys

1➤ Which of the following component is usually fabricated out of silicon steel ?

1 pointA. BearingsB. ShaftC. Stator coreD. None of the above

2➤ The frame of an induction motor is usually made of ____

1 pointA. silicon steelB. cast ironC. aluminiumD. bronze

3➤ The shaft of an induction motor is made of _____

1 pointA. stillB. flexibleC. hollowD. any of the above

4➤ The shaft of an induction motor is made of

1 pointA. high speed steel B. stainless steelC. carbon steelD. cast iron

5➤ In an induction motor, no-load the slip is generally

1 pointA. less than 1% B. 1.5%C. 2%D. 4%

6➤ In medium sized induction motors, the slip is generally around

1 pointA. 0.04% B. 0.4% C. 4%D. 14%

7➤ In squirrel cage induction motors, the rotor slots are usually given slight skew in order to

1 pointA. reduce windage lossesB. reduce eddy currentsC. to eliminate magnetic locking between stator and rotor and to reduce magnetic helm.D. reduce accumulation of dirt and dust

8➤ In case the air gap in an induction motor is increased

1 pointA. the magnetising current of the rotor will decreaseB. the power factor will decreaseC. speed of motor will increaseD. the windage losses will increase

9➤ Slip rings are usually made of

1 pointA. copper B. carbonC. phospor bronzeD. aluminium

10➤ In Ns is the synchronous speed and s the slip, then actual running speed of an induction motor will be

1 pointA. Ns B. s.NC. (l-s)NsD. (Ns-l)s

11➤ The efficiency of an induction motor can be expected to be nearly

1 pointA. 60 to 90% B. 80 to 90% C. 95 to 98%D. 99%

12➤ The number of slip rings on a squirrel cage induction motor is usually

1 pointA. twoB. threeC. fourD. none

13➤ The starting torque of a squirrel-cage induction motor is

1 pointA. low B. negligibleC. same as full-load torque D. slightly more than full-load torque

14➤ A double squirrel-cage induction motor has

1 pointA. two rotors moving in oppsite directionB. two parallel windings in statorC. two parallel windings in rotorD. two series windings in stator

15➤ Star-delta starting of motors is not possible in case of

1 pointA. single phase motorsB. variable speed motorsC. low horse power motorsD. high speed motors

16➤ The term 'cogging' is associated with

1 pointA. three phase transformersB. compound generatorsC. D.C. series motorsD. induction motors

17➤ In case of the induction motors the torque is

1 pointA. inversely proportional to (Vslip)B. directly proportional to (slip)2C. inversely proportional to slipD. directly proportional to slip

18➤ An induction motor with 1000 r.p.m. speed will have

1 pointA. 8 poles B. 6 polesC. 4 polesD. 2 poles

19➤ The good power factor of an induction motor can be achieved if the average flux density in the air gap is

1 pointA. absent B. smallC. largeD. infinity

20➤ An induction motor is identical to

1 pointA. D.C. compound motorB. D.C. series motorC. synchronous motorD. asynchronous motor

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