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AC Motor Review Problems, Exercises of Electrical Engineering

University of the Philippines Open UniversityElectrical Engineering

AC Motor Review Problems AC Motor Review Problems

Typology: Exercises

2024/2025

Available from 04/05/2025

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jason-morales-5 🇵🇭

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Induction Motor Review Problems
1. A three-phase, 4-pole, 60 Hz induction motor has a full load speed of 1750 rpm. What is the slip
speed?
A. 50 rpm C. 54 rpm
B. 1746 rpm D. 1800 rpm
2. An induction motor runs at 1164 rpm. What is the slip?
A. 3% C. 2%
B. 4% D. 5%
3. An induction motor runs at 1150 rpm. What is the frequency of the rotor?
A. 1 Hz C. 57.9 Hz
B. 19 Hz D. 2.5 Hz
4. A 4-pole induction motor running with 5% slip is supplied by a 6 pole synchronous generator driven at
1200 rpm. What is the motor speed?
A. 1200 rpm C. 1710 rpm
B. 950 rpm D. 1728 rpm
5. A 3-phase induction motor has rotor resistance and standstill reactance of 0.1 ohm and 3.5 ohm per
phase respectively. The rotor emf at standstill is 60 volts per phase, for a slip of 5%, what is the
power developed?
A. 1.7 hp C. 10 hp
B. 75 hp D. 15 hp
6. The rotor of a 3-phase, 60Hz , 4-pole induction motor takes 120 kW at 3 Hz. Determine the rotor
copper losses.
A. 16 kW C. 6 kW
B. 4 kW D. 8 kW
7. A 20 hp, 3-phase, 400-V, 60-Hz, 4-pole induction motor delivers full-load at 5% slip. The mechanical
rotational losses are 400 W. Calculate the rotor copper loss.
A. 806.3 W C. 746 W
B. 860.3 W D. 803.6 W
8. A 6-pole three-phase, 60Hz wound rotor induction motor delivers 25 hp at 1150 rpm. If the rotational
losses of the motor are 300 watts, what is the rotor input?
A. 18.95 kW C. 21.74 kW
B. 19.77 kW D. 22.66 kW
9. A 3Φ, 6-pole, 50Hz induction motor develops 3.73 kW at 960 rpm. What will be the stator input if the
stator loss is 280 watts?
A. 4165 W C. 4615 W
B. 4500 W D. 3855 W
10. A 3-phase, 6-pole induction motor is rated 400 Hz, 150 V, 10hp, 3% slip at rated power output. The
windage and friction loss is 200 W at rated speed. With the motor operating at rated voltage,
frequency slip and power output, determine the output torque.
A. 9.2 N-m C. 8.2 N-m
B. 10.4 N-m D. 7.2 N-m
11. A 6-pole, 3-phase, 60 Hz induction motor takes 48kW in power at 1140 rpm. The stator copper loss is
1.4 kW, stator core loss is 1.6 kW and rotor mechanical losses are 1 kW. Find the motor efficiency.
A. 87% C. 88%
B. 86% D. 89%
12. A 20 hp, 3-phase, 4-pole, 60 Hz, 230 volts induction motor is operating at full load speed of 1140 rpm.
The mechanical rotational losses are 300 Watts. What is the electromagnetic torque?
A. 125 N-m C. 127.5 N-m
B. 85.5 N-m D. 95.5 N-m
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Induction Motor Review Problems

  1. A three-phase, 4-pole, 60 Hz induction motor has a full load speed of 1750 rpm. What is the slip speed? A. 50 rpm C. 54 rpm B. 1746 rpm D. 1800 rpm
  2. An induction motor runs at 1164 rpm. What is the slip? A. 3% C. 2% B. 4% D. 5%
  3. An induction motor runs at 1150 rpm. What is the frequency of the rotor? A. 1 Hz C. 57.9 Hz B. 19 Hz D. 2.5 Hz
  4. A 4-pole induction motor running with 5% slip is supplied by a 6 pole synchronous generator driven at 1200 rpm. What is the motor speed? A. 1200 rpm C. 1710 rpm B. 950 rpm D. 1728 rpm
  5. A 3-phase induction motor has rotor resistance and standstill reactance of 0.1 ohm and 3.5 ohm per phase respectively. The rotor emf at standstill is 60 volts per phase, for a slip of 5%, what is the power developed? A. 1.7 hp C. 10 hp B. 75 hp D. 15 hp
  6. The rotor of a 3-phase, 60Hz , 4-pole induction motor takes 120 kW at 3 Hz. Determine the rotor copper losses. A. 16 kW C. 6 kW B. 4 kW D. 8 kW
  7. A 20 hp, 3-phase, 400-V, 60-Hz, 4-pole induction motor delivers full-load at 5% slip. The mechanical rotational losses are 400 W. Calculate the rotor copper loss. A. 806.3 W C. 746 W B. 860.3 W D. 803.6 W
  8. A 6-pole three-phase, 60Hz wound rotor induction motor delivers 25 hp at 1150 rpm. If the rotational losses of the motor are 300 watts, what is the rotor input? A. 18.95 kW C. 21.74 kW B. 19.77 kW D. 22.66 kW
  9. A 3Φ, 6-pole, 50Hz induction motor develops 3.73 kW at 960 rpm. What will be the stator input if the stator loss is 280 watts? A. 4165 W C. 4615 W B. 4500 W D. 3855 W
  10. A 3-phase, 6-pole induction motor is rated 400 Hz, 150 V, 10hp, 3% slip at rated power output. The windage and friction loss is 200 W at rated speed. With the motor operating at rated voltage, frequency slip and power output, determine the output torque. A. 9.2 N-m C. 8.2 N-m B. 10.4 N-m D. 7.2 N-m
  11. A 6-pole, 3-phase, 60 Hz induction motor takes 48kW in power at 1140 rpm. The stator copper loss is 1.4 kW, stator core loss is 1.6 kW and rotor mechanical losses are 1 kW. Find the motor efficiency. A. 87% C. 88% B. 86% D. 89%
  12. A 20 hp, 3-phase, 4-pole, 60 Hz, 230 volts induction motor is operating at full load speed of 1140 rpm. The mechanical rotational losses are 300 Watts. What is the electromagnetic torque? A. 125 N-m C. 127.5 N-m B. 85.5 N-m D. 95.5 N-m
  1. It is a part of three phase induction motor responsible in creating the revolving magnetic flux. A. Rotor B. stator C. slip ring D. armature
  2. The power factor of an induction motor is ____. A. Leading B. Lagging C. Unity D. Zero
  3. It is also known as the actual speed of induction motor A. synchronous speed B. rated speed C. rotor speed D. full load speed
  4. It is advisable to avoid line starting current of induction motor and used starter because A. starting torque is high B. motor takes three to seven times of its full load current C. it will pick up a very high speed and may run-away D. it will run in full voltage
  5. What are the two primary parts of a three-phase induction motor? A. rotor and stator C. slip ring and brushes B. stator and field D. rotor and armature
  6. For efficient operation, induction motors are always designed with a small A. air gap B. voltage drop C. inductive reactance D. impedance
  7. Which of the following motors produce lagging power factor? A. induction motor B. series motor C. compound motors D. synchronous motors
  8. What is in brief, the basis of operation of a 3-phase induction motor? A. motor is started B. motor is excited C. magnetic field is shorted D. revolving magnetic field is produced when a 3-phase stator winding is fed from a 3-phase supply