Electrical Engineering · Question Bank

3P Induction Motors

135 questions · page 3 of 7. Answer in your head first, then check the solution.

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TypeAll 135Problem solving 47Objective 88
DifficultyAll 135Easy 115Medium 18Hard 2
#41📜 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
#42📜 EE Pre-Board March 2017📘 PowerhouseEasy
Wye-delta starting is equivalent to autotransformer starting with __________ tapping.
A33%
B58%
C85%
D52%
#43📜 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
#44📜 EE Pre-Board August 2017📘 PowerhouseMedium
A three-phase, 4-pole, 60 Hz induction motor has a rotor resistance of 0.02 Ω/phase and a standstill reactance of 0.5 Ω/phase. Calculate the speed at which the maximum torque is developed.
A1,800 rpm
B1,793 rpm
C1,656 rpm
D1,728 rpm
#45📜 EE Pre-Board August 2017📘 PowerhouseEasy
Slip rings are made of
Acarbon
Bcopper
Cmica
Dcast iron
#46📜 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
#47📜 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
#48📜 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
#49📜 EE Pre-Board August 2017📘 PowerhouseMedium
A 3Φ, 6-pole, 50 Hz induction motor develops 3.73 kW at 960 rpm. What will be the stator input if the stator loss is 200 watts?
A3,885 W
B4,165 W
C3,930 W
D4,085 W
#50📜 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
#51📜 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
#52📜 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
#53📜 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
#54📜 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
#55📜 EE Pre-Board March 2018📘 PowerhouseHard
A six-pole three-phase 440-v, 60 Hz induction motor develops 10-hp at 1,150 rpm, the power factor being 80% lagging. Stator and core losses amount to 400 w and 350 w, respectively. Frictional losses amount to 0.5-hp. Calculate the motor line current.
A12.24 A
B13.41 A
C11.42 A
D14.64 A
#56📜 EE Pre-Board March 2018📘 PowerhouseMedium
A three-phase, 6 pole, 50 Hz induction motor develops a maximum torque of 30 N·m at 960 rpm. Calculate the torque produced by the motor at 6% slip. The rotor resistance per phase is 0.6 Ω.
A24.7 N-m
B25.7 N-m
C26.7 N-m
D27.7 N-m
#57📜 EE Pre-Board August 2018📘 PowerhouseMedium
A 440V, 60Hz, 6 pole, 3 phase induction motor has a rotor input power of 33kW at rated voltage and frequency. Under this condition, the rotor emf makes 126 complete cycles/minute. Find the rotor resistance in ohms/phase if the rotor current is 60A/phase.
A0.0118
B0.0107
C0.107
D0.118
#58📜 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
#59📜 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
#60📜 EE Pre-Board August 2018📘 PowerhouseMedium
A 15 hp, 460 V, 60 Hz, 6-pole, 3 phase induction motor has full-load slip of 4%. Find the full-load torque in N-m.
A85
B88
C93
D90

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