Electrical Machines Questions and Answers – Starting of Polyphase Induction Motors-I

This set of Electrical Machines Multiple Choice Questions & Answers (MCQs) focuses on “Starting of Polyphase Induction Motors”.

1. Voltage induce in the induction motor is highest at __________
a) starting
b) standstill
c) rated speed
d) any of the mentioned
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2. Starters are required in the induction motor because __________
a) of high starting current
b) they are not self starting
c) torque produced is very low at starting to overcome inertia
d) all of the mentioned
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3. Full voltage starting of induction motor may cause __________
a) dip in the voltages
b) high inrush current
c) high losses
d) all of the mentioned
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4. For a 4-pole, 50 Hz induction motor has starting current as 5 times to that of the full load current working at a speed of 1450rpm. The ratio of starting to full load torque will be?
a) 0.83
b) 0.17
c) 0.67
d) 1
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5. Starting methods applicable to both squirrel-cage and slip ring induction motors is/are __________

A. DOL starting
B. Auto transformer starting
C. Rotor resistance starting

a) A, B
b) A, B, C
c) B, C
d) A, C
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6. The method which employs reduction of the voltage while induction motor starting is?

A. DOL starting
B. Auto transformer starting

a) Only A
b) A, B
c) Only B
d) Neither A nor B
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7. The method which employs raising of the voltage while induction motor starting is?

A. DOL starting
B. Auto transformer starting

a) Only A
b) A, B
c) Only B
d) Neither A nor B
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8. External methods of induction motor starting is employed to __________
a) Reduce the voltage
b) Reduce the current
c) Improve efficiency
d) All of the mentioned
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9. A 3-phase, 4-pole, 50 Hz induction motor is uses DOL method of starting. It is later replaced by reactance method of starting with a fraction of ‘x’, then the starting current reduces by?
a) x
b) x^2
c) 1/x
d) no change in the starting current
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10. A 3-phase, 4-pole, 50 Hz induction motor is uses DOL method of starting. It is later replaced by reactance method of starting with a fraction of ‘x’, then the starting torque reduces by?
a) x
b) x^2
c) 1/x
d) no change in the starting current
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11. Series reactor method of starting has main disadvantage of __________
a) lowering the starting power
b) increasing the starting current
c) increasing starting torque
d) all of the mentioned
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12. Series reactor method of starting has main disadvantage of lowering the starting power. This can be overcome by __________
a) using series resistance
b) using parallel reactor
c) using parallel resistance
d) using series reactor
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13. A 3-phase, 4-pole, 50 Hz induction motor is uses DOL method of starting. It is later replaced by auto transformer method of starting with a tapping ratio of ‘x’, then the starting current reduces by?
a) x
b) x^2
c) 1/x
d) no change in the starting current
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14. A 3-phase, 4-pole, 50 Hz induction motor is uses DOL method of starting. It is later replaced by auto transformer method of starting with a tapping ratio of ‘x’, then the starting torque will be?
a) x *Tfl
b) x^2 *Tfl
c) 1/x *Tfl
d) no change in the starting current
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15. For the application requiring high starting torque and minimum starting current, the most suitable starting method will be?
a) Auto transformer starting method
b) Reactance starting method
c) DOL method
d) Star-Delta method
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16. Auto transformer method of starting has most acceptable method for the starting of the induction motor due to __________
a) maximum torque
b) maximum reduction of inrush current
c) variable tapping
d) all of he mentioned
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Sanfoundry Global Education & Learning Series – Electrical Machines.

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