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AC Motor Review Problems: A Comprehensive Guide to Understanding Induction Motor Concepts, Exercises of Electrical Engineering

University of the Philippines Open UniversityElectrical Engineering

A series of review problems designed to test understanding of ac motor concepts, particularly focusing on induction motors. The problems cover various aspects of induction motor operation, including slip speed, rotor frequency, power development, rotor copper losses, and motor efficiency. Valuable for students and professionals seeking to solidify their knowledge of ac motor principles.

Typology: Exercises

2024/2025

Available from 04/05/2025

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jason-morales-5 🇵🇭

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AC 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%
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Download AC Motor Review Problems: A Comprehensive Guide to Understanding Induction Motor Concepts and more Exercises Electrical Engineering in PDF only on Docsity!

AC 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%
  1. 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
  2. What happens to the frequency when the speed of the alternator is increase? A. decrease C. increase B. remain constant D. changes
  3. 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
  4. Synchronous Speed of a motor is directly proportional to A. Frequency B. Pole C. Slip Ring D. Magnetic Flux
  5. The power factor of an induction motor is ____. A. Leading B. Lagging C. UnityD. Zero
  6. Motors commonly used in home appliances such as blenders, mixers, etc. A. Universal motor C. Capacitors start and run motor B. Capacitor start motor D. Compound motor
  7. If the load is removed from a series wound motor, the speed will A. remains the same B. decrease C. increase D. none of these
  8. One of the biggest problem in split phase induction motor is A. noise C. that it cannot be started at full voltage B. high starting current D. all of these
  9. What is the ratio of output power to input power? A. Demand factor B. Power factorC. Gain D. Efficiency
  10. Which type of ac motors are used for high starting torque and low starting current applications? A. squirrel cage motor C. compound wound motor B. wound rotor motor D. synchronous motor
  11. It is also known as the actual speed of induction motor A. synchronous speed B. rated speed C. rotor speed D. full load speed
  12. A floating synchronous motor is A. Synchronous condenser C. capacitor B. Synchronous generator D. none of the above
  13. The rated frequency of the output voltage of an AC generator depends upon A. power factor B. excitation C. load D. number of poles
  14. Alternators are usually designed to generate A. Variable frequency C. Definite Frequency B. Definite Current D. Definite Power Factor
  15. When single phase is connected in high voltage source, the winding is connected in ___? A. series B. series in parallel C. parallel D. none of these
  16. The prime mover for large AC generador A. steam turbine B. hydraulic turbine C. gas turbine D. all of these

a. Skein winding b. Lap winding c. Wave winding d. Concentric winding

  1. Excitation current is used in which of the following motors? a. synchronous b. wound rotor c. induction d. squirrel cage
  2. In a large alternator, which of the following is normally negligible? a. reactance of winding c. impedance of winding b. resistance of winding d. current of winding
  3. 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
  4. For a ceiling fan, which of the single-phase motor is used? a. split-phase type c. permanent capacitor type b. capacitor start & run type d. capacitor start type
  5. For efficient operation, induction motors are always designed with a small a. air gap b. voltage drop c. inductive reactance d. impedance
  6. What motor is best suited to drive small electric fans? a. universal motor c. capacitor run motor b. shunt motor d. resistance split-phase motor
  7. Which of the following electric machine is equipped with slip rings? a. dc motor or dc generator c. ac generator b. split-phase motor d. repulsion type motor
  8. Which of the following motors produce lagging power factor? a. induction motor b. series motor c. compound motors d. synchronous motors
  9. 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
  10. Alternator synchronization means ___. a. connecting alternators in parallel c. adjustment in field excitations b. connecting alternators in series d. load sharing between alternators