THREE PHASE INDUCTION MOTORS QUIZ

The rotor of induction motor

Always revolves in the direction of stator flux

Always revolves in the direction opposite to stator flux

Insufficient data

None of the listed here

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YOUR ANSWER : ?

The synchronous speed of a 3-phase induction motor having 20 poles and connected to a 50 Hz source is _____

600 rpm

1200 rpm

1000 rpm

300 rpm

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Very large 3-phase induction motors (greater than 25 HP) are started _____

None of the listed here

By auto transformer starting

Star-delta starting

Direct on line

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In an induction motor, no load the slip is generally

1.5 %

Less than 1%

2%

4%

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DOL starting of induction motors is usually restricted to

Variable speed motors

High horsepower motors

High speed motors

Low horsepower motors

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If a 3-phase induction motor is running at slip S, then rotor copper loss is equal to

(1+S) × rotor input

(1-S) × rotor input

None of the listed here

S × rotor input

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3-phase wound rotor morors are also called _____ motors.

Series

Commutator

Synchronous

Slip ring

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The frequency of rotor current in a 6-pole , 50 Hz, 3-phase induction motor running at 950 rpm is

1.5 Hz

0.05 Hz

2.5 Hz

5 Hz

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Reduced voltage starter can be used with

Squirrel cage induction motor only but not with slip ring motor

None of these

Squirrel cage as well as slip ring induction motor

Slip ring motor only but not with squirrel cage induction motor

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At no load the rotor core loss of a 3 phase induction motor is

Small

Large

Practically zero

None of the listed here

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