Wireman – Semester 3, Module 8 - AC 3 Phase Induction motor

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Common for Wireman Trade 2nd Year

NAME *

NAME OF THE ITI *

MOBILE NUMBER *

1 : What is the speed of rotating magnetic field in a 3f induction motor? *

2 points

A : Rotor speed

B : Synchronous speed

C : Motor speed

D : Rated speed

2 : Which equation is used for calculation synetronous speed of 3f induction motor *

2 points

3: What is the synchronos is speed of a 3 phase induction motor if the supply frequency is 50Hz and number of pole is 4? *

2 points

A : 1400 rpm

B : 1500 rpm

C : 1450 rpm

D : 1000 rpm

4 : Name the part marked as X? *

2 points

A : Terminal box

B : Yoke/Irame

C : Stator winding

D : Laminated steel core

5 : Which material is used to wound rotor of squirrel cage induction motor? *

2 points

A : Aluminium

B : Enamelled copper conductor

C : Silicon steel

D : Copper bars

6 : Which part of squirrel cage rotor is short circuited? *

2 points

A : End rings

B : Shaft

C : End cover hysteresis

D : Bearings

7 : Why the core of 3 f induction motor is laminated? *

2 points

A : To reduce friction loss

B : To reduce eddy current loss

C : To reduce hysterism loss

D : To reduce starting current

8 : What is the equation for rotor frequency of 3-phase induction motor? *

2 points

9: Which formula is used to find percentage slip in 3 q induction? *

2 points

10 : Which speed of 3-phase induction motor runs? *

2 points

A : Above synchronous speed

B : Below synchronous speed

C : Equal to synchronous speed

D : At slip speed

11 : What is the value of slip at the time of starting of 3 phase induction motor? *

2 points

A : Two

B : Three

C : One

D : Zero

12 : Which is directly proportional to torque in 3 phase induction motor? *

2 points

A : Rotor power factor

B : Stator frequency

C : Number of poles

D : Supply voltage

13: What is phase angle difference between three windings in three phase squirrel cage induction motor? *

2 points

A : 360°

B : 90°

C : 120°

D : 30°

14 : Which material is used to wound outer cage rotor bars of a double squirrel-cage induction motor? *

2 points

A : Brass

B : Aluminium

C : Copper

D : Silicon steel

15: Which type of rotor is used in squirrel cage induction motor? *

2 points

A : Wound type

B : Squirrel cage

C : Slipring type

D : Projecting type

16 : Why rotor bars of squirrel cage induction motor is skewed? *

2 points

A : Reduce magnetic humming

B : Reduce losses

C : Improve efficiency

D : Improve capacity

17 : How to change the direction of rotation of a 3f squirrel cage induction motor? *

2 points

A : By interchanging three terminals

B : By interchanging any two terminals

C : By disconnecting one terminal

D : By reducing the applied voltage

18 : Which type of starter is recommended to start up to 3 HP squirrel cage induction motors? *

2 points

A : DOL starter

B : Auto transfer starter

C : Star-delta starter

D : Rotor resistance starter

19: Which starter is in simple expensive and easy to start? *

2 points

A : Rotor resistance starter

B : DOL starter

C : Semi automatic star delta starter

D : Auto transformer starter

20 : Which device in DOL starter provides effective protection against over load? *

2 points

A : Holding coil

B : Back up fuse

C : Thermal relay

D : Push button switch

21: How many number of contactors are used in a semi automatic star delta starter? *

2 points

A : 6

B : 4

C : 5

D : 3

22 : Which type of AC 3 phase motor starter this BIS symbol represents? *

2 points

A : Star delta starter

B : Rheostatic starter

C : Direct online starter

D : Pole changing starter

23 : Name the part marked as X in manual star delta starter? *

2 points

A : Plunger

B : Lever plate

C : Stop button

D : Over load relay setting

24 : Which is the additional device used in automatic star delta starter than semi automatic star delta starter? *

2 points

A : Push button station

B : Timer

C : OLR

D : Number of contacts

25 : How many times of starting current in 3f induction motor is reduced, while starting by star delta starter? *

2 points

26 : Which device is used in control of a star delta starter to stop the motor? *

2 points

A : OLR

B : Star contactor

C : Delta contactor

D : Normally closed push button

27 : What is the name of the starter symbol? *

2 points

A : D.O.L starter

B : Auto transformer starter

C : Automatic star/delta starter

D : Semi automatic star/delta starter

28 : What is the name of the A.C motor starter? *

2 points

A : DOL starter

B : Auto transformer starter

C : Semi automatic star delta starter

D : Fully automatic star delta starter

29: Which type of starter is used with reduced voltage tappings for 3 phase induction motor? *

3 points

A : D.O.L starter

B : Star delta starter

C : Auto transformer starter

D : Rotor resistance starter

30: How the voltage is reduced in auto transformer starter at the time of starting? *

2 points

A : By reducing supply voltage

B : By adjusting the tappings by handle

C : By using step down transformer

D : By adding resistance with rotor

31: Which induction motor, the external resistance is added to rotor circuit? *

2 points

A : Squirrel cage induction motor

B : Double squirrel cage induction motor

C : Slip ring induction motor

D : Single phase induction motor

32 : Which motor is used to produce high starting torque at variable speed? *

2 points

A : Repulsion motor

B : Permanent capacitor motor

C : 3 Phase slip ring induction motor

D : 3 Phase single squirrel cage induction motor

33 : Why slip ring induction motor is fitted with wound rotor? *

2 points

A : To reduce the slip

B : To control the speed

C : To reduce the losses

D : To get high starting and running torque

34: Which type of starter is used to start and run the 3 phase slip ring induction motor? *

2 points

A : Direct on-line starter

B : Rotor rheostat starter

C : Auto transformer starter

D : Manual star-delta starter

35 : What is the purpose of using rotor resistance starter to start 3 phase slip ring induction motor? *

2 points

A : Reduce rotor voltage

B : Increase rotor current

C : Increase the starting torque

D : Reduce the power loss

36 : Why external resistance is included in the rotor circuit at starting through 3 phase slipring induction motor starter? *

2 points

A : To get high running torque

B : To reduce high starting current

C : To reduce the load current

D : To get increased speed at starting

37 : What is the effect of motor, if the rotor windings in slipring induction motor is open circuited at starting? *

2 points

A : Will not run

B : Runs at slow speed

C : Runs at very high speed

D : Runs but not able to pull load

38: Which method is used to control the speed of 3 phase induction motor from stator side? *

2 points

A : By cascade operation

B : By rotor rheostat control

C : By injecting emf in rotor circuit

D : By changing the applied frequency

39 : Which speed control method of 3 f motor is used only induction motor supplied by generator? *

2 points

A : Casecade operation method

B : By changing the number of stator poles

C : By injection Emf in rotor circuit

D : By changing the supplied voltage

40 : Which method of speed control is only applicable for 3 phase slipring induction motor? *

2 points

A : Casecade operation method

B : Rotor rheostat speed control

C : Changing the applied frequency method

D : Changing the number of stator poles method

41 : Which method of speed control of 3 phase induction motor above and below normal speed can be obtained? *

2 points

A : By rotor rheostat control

B : By changing applied voltage

C : By injecting EMF in rotor circuit

D : By changing the number of stator poles

42 : Which method of speed control of 3 phase induction motor only two speeds can be obtained? *

2 points

A : By cascade operation

B : By changing the applied voltage

C : By changing the supply frequency

D : By changing the number of stator poles

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