Rotating Machines Midterm Practice
Induction Motor Mastery Quiz
Welcome to the Induction Motor Mastery Quiz, designed for electrical engineering enthusiasts and professionals alike. Test your knowledge on induction motors, their components, and operational principles through a comprehensive set of 74 questions.
Key Features:
- In-depth questions covering various aspects of induction motors
- Multiple choice format for an engaging experience
- Perfect for self-assessment and preparation for exams
The frame of an induction motor is usually made of
Silicon steel
Cast iron
Aluminium
Bronze
In an induction motor, no-load the slip is generally
Less than 1%
5%
2%
4%
The shaft of an induction motor is made of
Stainless steel
Carbon steel
Cast iron
Aluminium
The shaft of an induction motor must be of
Solid
Hollow
Flexible
Any of the above
Which of the following component is usually fabricated out of silicon steel?
Stator core
Bearings
Shaft
None of the above
Slip ring of an induction motor is usually made up of
Aluminium
Copper
Phosphorus Bronze
Carbon
A 3-phase 440 V, 50 Hz induction motor has 4% slip. The frequency of rotor current will be
50 Hz
25 Hz
5 Hz
2 Hz
The starting torque of a squirrel-cage induction motor is
Full-load torque
Slightly more than full-load torque
Low
Negligible
A 50 Hz, 3-phase induction motor has a full load speed of 1440 r.p.m. The number of poles in the motor is
2 pole
4 pole
6 pole
8 pole
A three phase, 50 Hz induction motor has a full load speed of 1440 rpm. The full load slip will be
3%
5%
4%
2%
The good power factor of an induction motor can be achieved if the average flux density in the air gap is
Inifinity
Large
Absent
Small
The crawling in the induction motor is caused by
High Loads
Low Voltage supply
Harmonic developed in the motor
Improper design of machine
The auto-starters (using three auto transformers) can be used to start cage induction motor of the following type
Delta connected only
Star connected only
Both 1 and 2
None of the above
If any two phases for an induction motor are interchanged
The motor will run in reverse direction
The motor will continue to run in the same direction
The motor will stop
The motor will Burn
An induction Motor is
Self-starting with high torque
Self-starting with zero torque
Self-starting with low torque
Not self-starting
In three-phase squirrel-cage induction motors
Rotor conductors are kept open
Rotor conductor ends are short-circuited through slip rings
Rotor conductors are short-circuited through end rings
Rotor conductors are connected to insulation
In a three-phase induction motor, the number of poles in the rotor winding is always
Equal to number of poles in stator
Zero
More than the number of poles in stator
Less than the number of poles in stator
Which of the following motor has high starting torque?
Wound rotor induction motor
Squirrel cage induction motor
Both 1 & 2
None of the above
At stand still condition the value of slip is
0
Infinity
One
None of the above
Rotor resistance speed control method is not applicable in
Slip Ring induction motor
Squirrel cage induction motor
Synchronous motor
None of the above
If the terminal voltage of an induction motor is decreased then current
Decreased
Increased
Remain same
None of the above
For starting of an induction motor, star/delta starting can be considered equivalent to an autotransformer starter with the ratio of
33.3%
50%
100%
57.7%
An induction motor is analogous to
Auto-transformer
Two windings transformer with secondary short circuited
Two windings transformer with secondary open circuited
Synchronous motor
A 4 pole 50 Hz induction motor is running at 1300 rpm. Find the speed of stator magnetic field with respect to the rotor?
1500 rpm
200 rpm
1300 rpm
3000 rpm
No load test of 3-phase induction motor used to determine
Variable loss
Constant loss
Eddy current loss only
Hysteresis loss only
Blocked rotor test in an induction motor is used to determine
Leakage impedance
Copper loss
Both 1 & 2
None of the above
Which of the following losses are negligible in blocked rotor test?
Mechanical losses
Iron losses
Both 1 & 2
None of the above
In induction generator operation the slip is always
Positive
Negative
Infinite
Zero
The rotor power output of a 3-phase induction motor is 30 kW and corresponding slip is 4%. The rotor copper loss will be
625 Watt
250 Watt
1000 Watt
1250 Watt
In an induction motor if the air gap is increased than which of the following statement is correct
Power factor will decrease
Power factor will increase
Speed will increase
Speed will decrease
If the applied rated voltage per phase is reduced to one-half, then the starting torque of squirrel cage induction motor becomes
4 times the initial value
2 times the initial value
1/4 of the initial value
1/2 times the initial value
The value of power factor of an induction motor operating at no load is
0.9 lagging
Unity
0.2 lead
0.2 lag
What is the ratio of rotor input power to rotor copper loss in an induction motor?
1/(1 - S)
1 - S
1/S
S
If an induction machine is run at above the synchronous speed it acts as
Synchronous Motor
Synchronous Generator
Induction Generator
None of the above
The best method to increase the starting torque of a 3-phase slip ring induction motor is
Rotor Resistance
Supply voltage
Supply Frequency
None of the above
A small air gap in 3 phase induction motor helps to
Reduce cogging effect
Reduce Crawling effect
Reduce Magnetizing effect
All of the above
Induction motors have the advantage of
Less maintenance
Less cost
Simple in construction
All of the above
If the frequency of 3-phase supply to the stator of a 3-phase induction motor is increased, then synchronous speed
Increased
Decreased
Remain unchanged
None of the above
A 3 phase induction motor is essentially a
Constant speed motor
Variable speed motor
Very costly
Easily maintainable
When the rotor of three phase induction motor is blocked then the slip is
0
0.5
0.1
1
An 8 pole, three phase induction motor is supplied from 50 Hz, a.c. supply. On full load, the frequency of induced EMF in the rotor is 2 Hz. Then the full load slip and the corresponding speed.
4% & 750
4 & 720
5% & 1000
5% & 1500
A 4 pole, 3 phase, 50 Hz induction motor runs at a speed of 1470 r.p.m. speed. Then the frequency of the induced e.m.f. In the rotor under this condition
1 Hz
2 Hz
5 Hz
6 Hz
The direction of rotation of 3-Φ induction motor is clockwise when it is supplied with the 3-Φ sinusoidal voltage having phase sequence of A-B-C. For counterclockwise rotation, the phase sequence of the power supply should be
B-C-A
A-C-B
C-A-B
Any of the above
The rotor winding of a 3-phase wound rotor induction motor is generally ............. connected.
Delta
Star
Partially Delta & Partially Star
None of the above
An eight-pole wound rotor induction motor operating on 60 Hz supply is driven at 1800 rpm by a prime mover in the opposite direction of revolving magnetic field. The frequency of rotor current is
120 Hz
180 Hz
60 Hz
200 Hz
In a wound rotor motor, the rotor winding is wound for poles ............. That of the stator winding.
Equal to
Greater than
Smaller than
None of the above
The maximum EMF is induced in the rotor of a 3-phase induction motor when it
No-Load
Full-load
Half-load
Is blocked
The power supplied to a three-phase induction motor is 32 kW and the stator combined losses are 1200 Watt. If the slip is 5 percent. Determine the rotor copper loss
2.8 kW
3.5 kW
4 kW
1.54 kW
From the above question find the total mechanical power developed by the Rotor
30.28 kW
29.26 kW
25.2 kW
14.45 kW
Find the output power of the motor if friction and windage losses are 175 Watts.
29.26 kW
28.51 kW
30.43 kW
14.56 kW
Find the efficiency of the induction motor neglecting rotor iron loss.
100%
50
25%
89%
The reactance of the rotor circuit of a 3-phase induction motor is maximum at
Full load
Half Load
Half Full load
Starting
A 3 phase, 400-V, 50 Hz 4 pole induction motor is fed from a 3-phase supply and runs of 1425 rpm. The frequency of the rotor emf is
2.5 Hz
50 Hz
48 Hz
Zero
If the stator voltage of a squirrel cage induction motor is reduced to 50 percent of its rated value, the torque developed is reduced by how many percentages of its full load value?
50%
25%
75%
57.7%
The rotor current in a 3-phase induction motor is .............. slip.
Directly proportional to
Inversely Proportional to
Independent
None of the above
A three-phase, four-pole, 50 Hz induction motor rotates at a full-load speed of 1470 rpm. The EMF measured between the slip-ring terminals when the rotor is not rotating is 200 V. The rotor windings are star connected and has resistance and stand-still reactance per phase of 0.1 Ω and 1.0 Ω. respectively. Then the rotor current on full load is
25 A
15.43
22.5 A
11.2 A
At starting, rotor reactance of a 3-phase induction motor is ............ As compared to rotor resistance.
Small
Equal to.
Large
None of the above
When an induction motor is running at full-load, rotor reactance is ............ Rotor resistance.
Very large
Large
Comparable
None of the above
If the slip of a 3-phase induction motor increases, the p.f. Of the rotor circuit is
Decreased
Remain unchanged
Increased
None of the above
A 3-Phase wound rotor induction motor having a star-connected rotor has an induced e. m.f. of 80 volts between slip-rings at standstill on open-circuit. The rotor has a resistance and reactance per phase of 1 Ω and 4 Ω respectively. Calculatecurrent/phase and power factor of the rotor when slip ring is connected to star-connected rheostat of 3Ω per phase.
8.16 A, 0.707
14.23 A, 0.5
1.34 A, 0.707
12.78 A, 0.5
If the supply voltage of a 3-phase induction motor is increased two times, then, torque is
Increased 4 time
Decreased 4 Times
Increased twice
Remain same
The 3-phase induction motor is so designed that the rotor should have ........... Under running conditions.
High resistance
Low resistance
Large slip
High reactance
If a 3-phase induction motor is running at slip s, then, rotor copper loss is equal to
(1 - s) x Rotor Input
(1 + s) x Rotor input
S x Rotor input
S x stator input
If an induction motor is running at slip s, then rotor output is
(1 - s) x Rotor input
(1 + s) x Rotor input
S x Rotor input
None of the above
A 3 phase induction motor has the facility for pole changing from 4 to 6. When it is operating as a 4 pole machine on 440V, 50Hz balanced 3 Phase supply,the frequency of rotor current is 3Hz. Then the speed of the motor is
1500 RPM
1200 RPM
1360 RPM
1410 RPM
If the motor were to run at 65% speed as in ‘the given above question, but operate as a 6 pole machine, what will be the slip and frequency of the rotor currents?
4.175 Hz
3.286 Hz
2.458 Hz
1.432 Hz
For a slip of 0.05, find the ratio of rotor speeds with the motor operating with 4 and 6 poles respectively.
2.8
1.5
3.2
4.5
At no-load, the Iron loss of a 3-phase induction motor is
Practically Zero
Large
Small
None of the above
For higher efficiency of 3-phase induction motor, the slip should be
Unity
Large
As small as possible
Very large
A 3-phase induction motor is running at 2% slip. If the input to rotor is 1000 W, then mechanical power developed by the motor is
500 W
200 W
20 W
980 W
The approximate efficiency of a 3-phase, 50 Hz, 4-pole induction motor running at 1350 r.p.m. is
90%
60%
45%
100%
If the air gap between the rotor and stator of a 3-phase induction motor isincreased, then
No load current is increasd
Leakage reactance is decreased
Leakage reactance is increased
Any of the above
The conditions of an induction motor at no-load resemble those of a transformer whose secondary is
Short-circuited
Open-circuited
Supplying a variable resistive load
None of the above
The speed of a squirrel cage induction motor is changed by
Cascade Connection
Rheostatic control
Pole changing method
Any of the above
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