ELECTRICAL MACHINE QUIZ

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ELECTRICAL MACHINE QUIZ_41

3-PHASE I.M MOTOR_4

Q.46 An induction motor under normal running condition

1 point

the slip is of order of 3%

rotor frequency is about 1.5 Hz for stator frequency of 50 Hz

Both A and B

rotor frequency is about 50 Hz for stator frequency of 1.5 Hz

Clear selection

Q.47 A three phase induction motor is

1 point

self starting

starting current is very large

at starting the motor slip is unity

all of the above

Clear selection

Q.48 The purpose of starter used in induction motor are

1 point

to reduce the heavy starting current

to provide under voltage protection

to provide over load protection

all of the above

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Q.49 The starters commonly used for cage type induction motors are

1 point

star-delta starter

direct online starter

Autotransformer

all of the above

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Q.50 In which type of starter, a induction motor is directly connected to the full supply voltage

1 point

star-delta starter

direct online starter

Autotransformer

all of the above

Clear selection

Q.51 A direct online starting is

1 point

simple and cheap method

D.O.L starter used for small motor upto 5KW

It provides under and over voltage protection

all of the above

Clear selection

Q.52 A star-delta starter is used for _____ designed to run normally on __ winding.

1 point

wound rotor motor; delta connected rotor

cage rotor motor; delta connected stator

wound rotor motor; delta connected stator

cage rotor motor; delta connected rotor

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Q.53 In three phase induction motor, by connecting the stator windings first in star and then in delta, the line current drawn by the motor at starting is ________as compared to line current drawn by the motor at starting with delta connection.

1 point

reduced to one-third

increases to one-third

reduced to one-fourth

increase to one-fourth

Clear selection

Q.54 In star delta starter

1 point

Vph = VL /√3

starting torque is directly proportional to square of voltage

starting torque is reduces to one –third that obtainable in delta-delta

all of the above

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Q.55 An autotransformer starter is

1 point

suitable for delta connected motor

suitable for star connected Motor

provides with tapings

all of the above

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Q.56 In autotransformer starter the starting current is limited to

1 point

reduced the initial stator current

reduced the initial stator voltage applied

reduced the initial load current

reduced the field current

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Q.57 A star delta starter is

1 point

cheaper than auto transformer

commonly used for small and medium size motors

Both A and B

costly than autotransformer

Clear selection

Q.58 The efficiency of the motors can be found by performing

1 point

no-load test

blocked rotor test

regenerative test

Both A and B

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Q.59 At no load on motors

1 point

power factor is less than 0.5

total input power is equal to constant loss, friction and windage losses of the motor

no load current is 20-30% of the full load current

all of the above

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Q.60The friction and windage losses can be separated from

1 point

open circuit test

blocked rotor test

regenerative test

any of the above

Clear selection

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