Induction Motor MCQ Part 4

Electrical Engineering MCQ on Induction Motor.

## What is the approximate efficiency of a 3 phase, 4, 60 Hz induction motor running at an RPM 1200

What is the approximate efficiency of a 3 phase, 4, 60 Hz induction motor running at an RPM 1200:

- 50%
- 66.66%
- 78.98%
- 86%

Correct answer: 2. 66.67%

Solution:

Solution: Ns = 120*f/P = 1800

s = (Ns – N)/Ns = 0.33

*Approximate efficiency = 1 – s = 1 – 0.33 = 0.66 = 66.66%*

## A voltmeter gives 180 oscillations per minute when connected to the rotor of the induction motor. Calculate the slip if the supply frequency is 60 Hz

A voltmeter gives 180 oscillations per minute when connected to the rotor of the induction motor. Calculate the slip if the supply frequency is 60 Hz:

- 2%
- 5%
- 8%
- 11%

Correct answer: 2. 5%

Solution:

f’ = 180/60 = 3

s = f’/f = 3/60 = 0.05 = 5%

## Value of rotor reactance as compared to rotor resistance at starting instance of 3 Phase Induction Motor

The rotor reactance of 3 phase induction motor at the instance of starting is ___________ as compared to rotor resistance:

- Smaller
- Identical
- Larger
- None of the above

Correct answer: 3. Larger

## If a 3 phase induction motor is running at certain slip s. Then rotor copper losses expressed mathematically are

If a 3 phase induction motor is running at certain slip s. Then rotor copper losses expressed mathematically are:

- s * rotor input
- (1 – s) * rotor input
- (1 + s) * rotor input
- 2s * rotor input

Correct answer: 1. s * rotor input

## The induction motor is best described in three words as

The induction motor is best described in three words as:

- Singly excited machine
- Doubly excited machine
- Triply fed machine
- Quad fed machine

Correct answer: 1. Singly fed excited machine

## More MCQ on Induction Motors

- The Correct Statement about DC field current in Induction Motor
- The Induction Motor Runs at the Speed
- The Correct Relationship between Slip, Synchronous, and Rotor speed of Induction Motor
- Formula for Synchronous Speed of Induction Machine
- Five
- The synchronous speed of 4 pole, 50 Hz induction Motor is
- A 4 pole, 60 Hz Induction Motor Has a Slip of 5%. The Speed of motor is
- A 4 pole, 50 Hz Induction Motor Has a Slip of 5%. The Speed of motor is
- Size of Single Phase Induction Motor vs Three Phase Induction Motor for Same Ratings
- Usually, a Single Phase Induction Motor has number of poles
- The rotor frequency of a 4 pole, 60 Hz induction motor having full load slip of 5% at rated load is
- If rotor of Induction motor is rotating at synchronous speed the torque will be
- What is No-load slip value in induction motor
- The current in the starting winding of capacitor-start single-phase motors has what relationship with voltage [49]
- What will happen to a single-phase motor when its capacitor is short-circuited
- With reference to a capacitor-start and run motor the function of the running capacitor in series with the auxiliary winding is
- WREF capacitor-start motor the phase displacement between starting and running winding can be nearly
- In a split-phase induction motor which winding is connected through centrifugal switch