Single phase IM PDF

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Single phase IM...

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1.In capacitor start single-phase motors

current in the starting winding leads the voltage current in the starting winding lags the voltage current in the starting winding is in phase with voltage in running winding none of the above ANSWER : s: a

2.If the capacitor of a single-phase motor is short-circuited

the motor will not start the motor will run the motor will run in reverse direction the motor will run in the same direction at reduced r.p.m. ANSWER : : the motor will not start

3.Which of the following motors is used in mixies ?

Repulsion motor Reluctance motor Hysteresis motor Universal motor ANSWER : : Universal motor

4.The value of starting capacitor of a fractional horse power motor will be

100 uF 00 uF 300 uF 400 uF ANSWER : s: c

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5.If a particular application needs high speed and high starting torque, then which of the following motor will be preferred ?

Universal motor Shaded pole type motor Capacitor start motor Capacitor start and run motor ANSWER : : Universal motor 6.In repulsion motor direction of rotation of motor

is opposite to that of brush shift is the same as that of brush shift is independent of brush shift is the same as that of brush shift ANSWER : In a single phase motor the centrifugal switch

7.Which of the following motor will have relatively higher power factor ?

Capacitor run motor Shaded pole motor Capacitor start motor Split phase motor ANSWER : : Capacitor run motor

8.Burning out of windings is due to

short circuited capacitor capacitor value hiving changed open circuiting of capacitor none of the above ANSWER : : short circuited capacitor

9.The range of efficiency for shaded pole motors is

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95% to 99% 80% to 90% 50% to 75% 5% to 35% ANSWER : : 5% to 35%

10.A capacitor-start single phase induction motor is switched on to supply with its capacitor replaced by an inductor of equivalent reactance value. It will

start and then stop start and run slowly start and run at rated speed not start at all ANSWER : : not start at all 11.In a capacitor start and run motors the function of the running capacitor in series with the auxiliary winding is to

improve power factor increase overload capacity reduce fluctuations in torque to improve torque ANSWER : : improve power factor

12.In a shaded pole single -phase motor, the revolving field is produced by the use of

inductor capacitor resistor shading coils ANSWER : : shading coils

13.Direction of rotation of a split phase motor can be reversed by reversing the connection of

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running winding only starting winding only either (a) or (b) both (a) and (b) ANSWER : : either (a) or (b)

14.The direction of rotation of an hysteresis motor is determined by

interchanging the supply leads position of shaded pole with respect to main pole retentivity of the rotor material none of these ANSWER : : position of shaded pole with respect to main pole

15.In a split phase motor

the starting winding is connected through a centrifugal switch the running winding is connected through a centrifugal switch both starting and running windings are connected through a centrifugal switch centrifugal switch is used to control supply voltage ANSWER : : the starting winding is connected through a centrifugal switch 16.The rotor developed by a single-phase motor at starting is

more than i.he rated torque rated torque less than the rated torque zero ANSWER : : zero

17.Which of the following motor will give relatively high starting torque ?

Capacitor start motor

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Capacitor run motor Split phase motor Shaded pole motor ANSWER : : Capacitor start motor

18.Which of the following motors is inherently self starting ?

Split motor Shaded-pole motor Reluctance motor None of these ANSWER : : Shaded-pole motor

19.Short-circuiter is used in

repulsion induction motor repulsion motor repulsion start induction run motor none of the above ANSWER : : repulsion start induction run motor

20.The power factor of a single-phase induction motor is usually

lagging always leading unity unity to 0.8 leading ANSWER : : lagging 21.In a shaded pole motor, the shading coil usually consist of

a single turn of heavy wire which is in parallel with running winding a single turn of heavy copper wire which is short-circuited and carries only induced current

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a multilayer fine gauge copper wire in parallel with running winding none of the above ANSWER : : a single turn of heavy copper wire which is short-circuited and carries only induced current

22.The running winding of a single phase motor on testing with meggar is found to be ground. Most probable location of the ground will be

at the end connections at the end terminals anywhere on the winding inside a slot at the slot edge where coil enters or comes out of the slot ANSWER : : at the slot edge where coil enters or comes out of the slot

23.A centrifugal switch is used to dis- connect 'starting winding when motor has

run for about 1 minute run for about 5 minutes picked up about 50 to 70 per cent of rated speed picked up about 10 to 25 per cent of rated speed ANSWER : : picked up about 50 to 70 per cent of rated speed

24.In a capacitor start motor, the phase displacement between starting and running winding can be nearly

10฀ 30฀ 60฀ 90฀ ANSWER : : 90฀

25.In a capacitor start single-phase motor, when capacitor is replaced by a resistance

torque will increase

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the motor will consume less power motor will run in reverse direction motor will continue to run in same direction ANSWER : : motor will continue to run in same direction Which of the following motors can be run on AC. as well as D.C. supply ?

Universal motor Repulsion motor Synchronous motor Reluctance motor ANSWER : : Universal motor

2.Which of the following motors will operate at high power factor ?

Shaped pole motor Split phase motor Capacitor start motor Capacitor run motor ANSWER : : Capacitor run motor

3.In split-phase motor iauxiliary winding is of

thick wire placed at the bottom of the slots thick wire placed at the top of the slots thin wire placed at the top of the slots thin wire placed at the bottom of the slots ANSWER : : thin wire placed at the top of the slots

4.In case of high speed universal motor which of the following needs more attention ?

End play Air gap

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Insulation in rotor Balancing of rotor ANSWER : : Balancing of rotor

5.In case of a shaded pole motor the direction of rotation of the motor is

from main pole to shaded pole from shaded pole to main pole either of the above depending on voltage either of the above depending on power factor ANSWER : : from main pole to shaded pole 6.In A.C. series motor compensating winding is employed to

reduce the effects of armature reaction increase the torque reduce sparking at the brushes none of the above ANSWER : : reduce sparking at the brushes

7.In a two value capacitor motor, the capacitor used for running purposes is

air capacitor paper spaced oilfilled type ceramic type a.c. electrolytic type ANSWER : : paper spaced oilfilled type

8.Which type of load is offered by cranes and hoists ?

Gradually varying load Non-reversing, no-load start Reversing, light start

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Reversing, heavy start ANSWER : s: d

9.Which of the following motors has highest starting torque ?

Repulsion motor Shaped pole motor Capacitor-start motor Split-phase motor ANSWER : : Capacitor-start motor

10.Which of the following single-phase motors has relatively poor starting torque ?

Universal motor Repulsion motor Capacitor motor All single phase motors have zero starting torque ANSWER : : Capacitor motor 11.The wattage of motor for driving domestic sewing machine will be around

100 to 150 W 40 to 75 W 10 to 30 W 5 to 10 W ANSWER : : 100 to 150 W

12.Single phase induction motor usually operates on

0.6 power factor lagging 0.8 power factor lagging 0.8 power factor leading unity power factor

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ANSWER : : 0.6 power factor lagging

13.The motor used on small lathes is usually

universal motor D.C. shunt motor single-phase capacitor run motor 3-phase synchronous motor ANSWER : : single-phase capacitor run motor

14.Which of the following motors can be used for unity power factor ?

Capacitor run motor Shaded pole motor Hysteresis motor Schrage motor ANSWER : : Schrage motor

15.A hysteresis motor works on the principle of

hysteresis loss magnetisation of rotor eddy current loss electromagnetic induction ANSWER : : hysteresis loss 16.The speed of a universal motor is generally reduced by using

gear trains V-belts brakes chains ANSWER : : gear trains

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17.The repulsion-start induction-run motor is used because of

good power factor high efficiency minimum cost high starting torque ANSWER : : high starting torque

18.Which of the following motors is preferred for tape -recorders ?

Shaded pole motor Hysteresis motor Two value capacitor motor Universal motor ANSWER : : Hysteresis motor

19.The wattage rating for a ceiling fan motor will be in the range

200 to 250 W 250 to 500 W 50 to 150 W 10 to 20 W ANSWER : : 50 to 150 W

20.Which of the following single-phase induction motors is generally used in time phonographs ?

Resistance start Capacitor start capacitor run Shaded pole Universal ANSWER : s: c

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21.A schrage motor can run on

zero slip negative slip positive slip all of the above ANSWER : : all of the above

22.Which of the following single-phase motors is suitable for timing and control purposes ?

Reluctance motor Series motor Repulsion motor Universal motor ANSWER : : Reluctance motor

23.Which of the following motor will give the highest starting torque ?

D.C. shunt motor Schrage motor Repulsion start and induction run motor Universal motor ANSWER : : Schrage motor

24.A universal motor can run on

A.C. only D.C. only either A.C. or D.C. none of the above ANSWER : : either A.C. or D.C.

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25.A single-phase induction motor is

inherently self-starting with high torque inherently self-starting with low torque inherently non-self-starting with low torque inherently non-self-starting with high torque ANSWER : : inherently non- self -starting with low torque 26.For which of the applications a reluctance motor is preferred ? Electric shavers Refrigerators Signalling and timing devices Lifts and hoists ANSWER : : Signalling and timing devices 1.Torque developed by a single phase induction motor at starting is

pulsating uniform none of the above nil ANSWER : : nil

2.As hysteresis motors are free from mechanical and magnetic vibrations therefore these are considered as suitable for

fans blowers sound equipment mixer grinders ANSWER : : sound equipment

3.In which single-phase motor, the rotor has no teeth or winding ?

Split phase motor

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Reluctance motor Hysteresis motor Universal motor ANSWER : : Hysteresis motor

4.The rotor of a hysteresis motor is made of

aluminium cast iron chrome steel copper ANSWER : : chrome steel

5.The speed control of universal motor used for sewing machines is by

friction varying the resistance tapping the field centrifugal mechanism ANSWER : : varying the resistance 6.In repulsion motor, maximum torque is developed when

brush axis is at 45฀ electrical to the field axis brush axis coincides with the field axis brush axis is at 90฀ electrical to the field axis none of the above ANSWER : : brush axis is at 45฀ electrical to the field axis

7.In a hysteresis motor, the rotor must have

retentivity resistivity

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susceptibility none of the above ANSWER : : retentivity

8.The motor used for the compressors is

d.c. series motor shaded pole motor capacitor-start capacitor-run motor reluctance motor ANSWER : : capacitor-start capacitor-run motor

9.The direction of rotation of universal motor can be reversed the by reversing the flow of current through

armature winding field winding either armature winding or field winding none of the above ANSWER : : either armature winding or field winding

10.A reluctance motor

is self-starting is constant speed motor needs no D.C. excitation all of the above ANSWER : : all of the above 11.Which of the following motors is used for unity power factor ?

Hysteresis motor Schrage motor Universal motor

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Reluctance motor ANSWER : : Schrage motor

12.The speed/load characteristics of a universal motor is same as that of

A.C. motor D.C. shunt motor D.C. series motor none of the above ANSWER : : D.C. series motor

13.In a ceilingfan employing capacitor run motor

secondary winding surrounds the primary winding primary winding surrounds the secondary winding both are usual arrangements none of the above ANSWER : : secondary winding surrounds the primary winding

14.Which motor is normally free from mechanical and magnetic vibrations ?

Split phase motor Universal motor Hysteresis motor Shaded pole motor ANSWER : : Hysteresis motor

15.Speed torque characteristic of a repulsion induction motor is similar to that of a D.C.

shunt motor series motor compound motor

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separately excited motor ANSWER : : compound motor 16.The shaded pole motor is used for

high starting torque low starting torque medium starting torque very high starting torque ANSWER : : low starting torque

17.Which of the following motors is used in a situation where load increases with speed ?

Induction motor Three-phase series motor Schrage motor Hysteresis motor ANSWER : : Three-phase series motor

18.In repulsion motor, zero torque is developed when

brush axis is 45฀ electrical to field axis brush axis coincides with the field axis brush axis is 90฀ electrical to field axis both (b) and (c) ANSWER : : both (b) and (c)

19.In split phase motor main winding is of

thin wire placed at the top of the slots thin wire placed at the bottom of the slots thick wire placed at the bottom of the slots thick wire placed at the top of the" slots

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ANSWER : : thick wire placed at the bottom of the slots

20.The electric motor used in portable drills is

capacitor run motor hysteresis motor universal motor repulsion motor ANSWER : : universal motor 21.The purpose of stator winding in the compensated repulsion motor is to

provide mechanical balance improve power factor and provide better speed regulation prevent hunting in the motor eliminate armature reaction ANSWER : : improve power factor and provide better speed regulation

22.The rotor slots, in an induction motor, are usually not quite parallel to the shaft because it

improves the efficiency helps the rotor teeth to remain under the stator teeth helps in reducing the tendency of the rotor teeth to remain under the stator teeth improves the power factor ANSWER : : helps in reducing the tendency of the rotor teeth to remain under the stator teeth

23.If the centrifugal switch does not open at 70 to 80 percent of synchronous speed of motor, it would result in

damage to the starting winding damage to the centrifugal switch overloading of running winding none of the above

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ANSWER : : damage to the starting winding

24.Which of the following applications always have some load whenever switched on ?

Vacuum cleaners Fan motors Pistol drills All of the above ANSWER : : Pistol drills 1.Most of the fractional horsepower motors have either

hard and annealed bearings ball or roller bearings soft and porous bearings plain or sleeve bearings ANSWER : : plain or sleeve bearings

2.After the starting winding of a single phase induction motor is disconnected from supply, it continues to run only on

running winding rotor winding field winding compensating winding ANSWER : : running winding

3.In a universal motor, the most common cause of brush sparking is

open armature winding shorted armature winding shorted field winding" high commutator mica

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ANSWER : : all of the above

4.Speed control of a universal motor is achieved by

varying field flux with tapped field windings connecting rheostat in series applying variable voltage by means of silicon controlled rectifier applying variable voltage by means of variable auto-transformer ANSWER : : all of the above methods

5.A universal motor is one which

can be operated either on D.C. or A.C. supply at approximately the same speed and output can be marketed internationally runs at dangerously high speed on no-load can be operated either on D.C. or A.C. supply at approximately the same speed and output ANSWER : A repulsion motor is equipped with 6.To reverse the direction of rotation of acapacitor start motor while it is running we should

disconnect motor from the supply till it stops then reconnect it to supply with reversed connection of main or auxiliary winding disconnect motor from supply and immediately reconnect it to supply with reversed connections of the main winding reverse the direction of connection of the auxiliary winding and after motor comes to rest then connect auxiliary winding to the supply reverse the direction of connections of the auxiliary winding and im-mediately connect it to supply ANSWER : : disconnect motor from the supply till it stops then reconnect it to supply with reversed connection of main or auxiliary winding

7.Which of the following motors is used in tape -recorders ?

Hysteresis motor Reluctance motor

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Capacitor-run motor Universal motor ANSWER : : Hys...