Electrical Engineering · Question Bank

3P Induction Motors

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#21📜 EE Pre-Board August 2015📘 PowerhouseEasy
A 12-pole, 3- phase alternator driven at a speed of 500 rpm supplies power to an 8-pole, 3-phase induction motor. If the slip of the motor at full-load is 3%, calculate the full-load speed of the motor.
A750 rpm
B734.5 rpm
C727.5 rpm
D742 rpm
#22📜 EE Pre-Board August 2015📘 PowerhouseEasy
If the stator voltage of a SCIM is reduced to 80% of its rated value, the torque developed is reduced by ____ percent of its full-load value.
A64
B36
C20
D40
#23📜 EE Pre-Board August 2015📘 PowerhouseEasy
An induction motor is analogous to
ATwo winding transformer with open circuit secondary
BTwo winding transformer with short circuit secondary
C3 winding transformer
DAutotransformer
#24📜 EE Pre-Board March 2016📘 PowerhouseEasy
A three-phase induction motor has a nameplate speed of 1,720 rpm. What is the rotor frequency?
A1.8 Hz
B2.7 Hz
C5Hz
D4.4 Hz
#25📜 EE Pre-Board March 2017📘 PowerhouseEasy
What is the formula for the synchronous speed of a motor?
A\(N_s = \dfrac{120P}{f}\)
B\(N_s = 120fP\)
C\(N_s = \dfrac{120f}{P}\)
D\(N_s = \dfrac{60f}{P}\)
#26📜 EE Pre-Board March 2017📘 PowerhouseEasy
The frequency of the emf in the stator of a 4-pole induction motor is 60 Hz, and that in the rotor is 2 Hz. At what speed is the motor running?
A1,720 rpm
B1,740 rpm
C1,760 rpm
D1,780 rpm
#27📜 EE Pre-Board March 2017📘 PowerhouseEasy
How much larger is the rotor reactance of a SCIM at start-up than it is when the motor operates at 5 percent slip?
A20 times
B10 times
C5 times
D25 times
#28📜 EE Pre-Board March 2017📘 PowerhouseEasy
Wye-delta starting is equivalent to autotransformer starting with __________ tapping.
A33%
B58%
C85%
D52%
#29📜 EE Pre-Board March 2017📘 PowerhouseEasy
A double squirrel-cage induction motor has
Atwo rotors moving in opposite direction
Btwo parallel windings in stator
Ctwo parallel windings in rotor
Dtwo series windings in stator
#30📜 EE Pre-Board August 2017📘 PowerhouseEasy
Slip rings are made of
Acarbon
Bcopper
Cmica
Dcast iron
#31📜 EE Pre-Board August 2017📘 PowerhouseEasy
A 3-phase, 4-pole induction motor with an open circuited rotor is connected to a 400 V, 50 Hz, 3-phase supply. The motor will run at _________ rpm.
A1,500
B1,440
C750
D0
#32📜 EE Pre-Board August 2017📘 PowerhouseEasy
A three-phase motor is rated 50 HP, 440 volts and 85% power factor. What is its rated current?
A48.9 A
B57.6 A
C99.7 A
D65.4 A
#33📜 EE Pre-Board August 2017📘 PowerhouseEasy
If there is an open circuit in the rotor of a slip-ring induction motor,
Ait will run at reduced speed
Bit will run at synchronous speed
Cthe motor will not start
Dit will draw very high starting current
#34📜 EE Pre-Board August 2017📘 PowerhouseEasy
A three-phase induction motor is taking 40 kW, the slip being 4%, and stator losses amount to 800 watts. Calculate the total power developed.
A37.63 kW
B38.40 kW
C39.20 kW
D36.86 kW
#35📜 EE Pre-Board August 2017📘 PowerhouseEasy
An induction motor with 8 poles, 60 Hz is operated with a slip of 3%. Calculate the rotor speed.
A900 rpm
B927 rpm
C873 rpm
D846 rpm
#36📜 EE Pre-Board March 2018📘 PowerhouseEasy
Three phase induction motor is more suitable than single phase because
AIt’s self-starting
Bit has better efficiency
Cit has better power factor
Dall of these
#37📜 EE Pre-Board March 2018📘 PowerhouseEasy
What is the speed of a 60 Hz induction motor of six poles if the percent slip is 2.5%?
A1462 rpm
B1170 rpm
C877 rpm
D1755 rpm
#38📜 EE Pre-Board March 2018📘 PowerhouseEasy
To reverse the direction of rotation of a three-phase induction motor, it is necessary to
Ainterchange all the three line connections
Breverse the polarity of the rotor circuit
Cincrease the resistance of the rotor circuit
Dinterchange any two of the three line connections
#39📜 EE Pre-Board August 2018📘 PowerhouseEasy
An induction motor with 8 poles, 60 Hz is operated with a slip of 3%. Calculate the rotor speed.
A1,684
B1,024
C873
D927
#40📜 EE Pre-Board August 2018📘 PowerhouseEasy
A 60 Hz, 4 pole, 3 phase induction motor has a slip of 2.5 %. What is the slip speed in rpm ?
A55
B40
C60
D45

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