Intro to Electric Motors 200

This class discusses how various types of electric motors are applied throughout industry and the principles behind motor operation. Includes an Interactive Lab.

Class Details

Class Name:
Intro to Electric Motors 200
This class discusses how various types of electric motors are applied throughout industry and the principles behind motor operation. Includes an Interactive Lab.
Number of Lessons:
Additional Language:
Related 2.0 Class:
Introduction to Electric Motors 301

Class Outline

  • Objectives
  • What Is an Electric Motor?
  • Motor Theory
  • Right-Hand Motor Rule
  • Speed and Torque
  • Horsepower
  • Motor Parts
  • Counter EMF
  • DC Motors
  • AC Motors
  • Motor Efficiency
  • Motor Control
  • Motor Safety and Maintenance
  • Summary


  • Define electric motors.
  • Describe the operating principles of electric motors.
  • Describe the right-hand motor rule.
  • Define speed.
  • Define torque.
  • Describe horsepower.
  • Identify the parts of an electric motor.
  • Describe counter emf.
  • Identify the main types of DC motors.
  • Identify the main types of AC motors.
  • Describe ways to evaluate speed regulation.
  • Describe ways to control motor speed.
  • Describe common safety practices for working with motors.


  • MSSC Maintenance Awareness


Vocabulary Term Definition
adjustable frequency drive A device that converts incoming 60Hz AC power into other desired frequencies to allow for motor speed control.
alternating current Current that regularly reverses the direction of its flow. In the U.S., AC alternates 60 times per second, or 60 hertz.
armature The part of a motor in which a current is induced by a magnetic field. The armature usually consists of a series of coils or groups of insulated conductors surrounding a core of iron.
armature winding The conducting coils that are wound around the armature in which voltage is induced, causing it to rotate within a magnetic field. If the wires are damaged or broken, the armature will not rotate properly.
brushes Sliding electrical contacts used to provide a connection between the armature and the external circuit.
commutator The rotating switch that contacts the brushes of a DC motor. The commutator maintains DC when the rotation of the armature switches the polarity of the conductor.
compound motor A DC motor that uses both series and shunt field windings. Compound motors provide most of the positives of both types.
constant speed motor A type of motor that maintains a steady rate of rpm from no load to full load. DC shunt motors are often referred to as constant speed motors because they have this characteristic.
copper loss A power loss due to current flowing through wire. The lost power is converted into heat.
counter emf The voltage induced in the armature of a DC motor that opposes the applied voltage and limits armature current.
direct current Current that travels in one direction. It does not reverse the direction of flow.
efficiency A measure of the work output of a system versus the total work supplied to it. An efficient system converts a greater percentage of input energy into useful work.
electromagnet A powerful magnet that gains an attractive force only when current passes through it.
electromotive force The force that pushes electrons through a conductor. Electromotive force is abbreviated "emf" and is measured in volts.
energy The ability to do work. Energy is measured in watt hours and is expressed as the product of power and time.
Faraday's Law A law that states an electric field is induced in any system in which a magnetic field is changing with time.
foot-pound In the English system, the unit used to measure power. Some sources use foot-pounds interchangeably with pound-feet to express torque.
frequency A measurement of the number of complete AC cycles that occurs in one second. Frequency is measured in Hertz (Hz).
friction A force that resists motion between two objects that are in contact with each other.
generator A device that converts mechanical energy into electrical energy by magnetic induction.
horsepower A unit of power used to describe machine strength. One horsepower equals 33,000 ft-lbs of work per minute, or 746 watts.
left-hand flux rule A method used to determine the relationship of the motion of the conductor in a magnetic field to the direction of the induced current. Flux rotates around the conductor as shown by the left hand.
load The opposition to applied force, such as a weight, to be carried or moved.
lockout/tagout A method of protecting employees from accidental machine startup through proper locking and labeling of machines that are undergoing maintenance.
machine guard A shield or cover over hazardous areas on a machine to prevent accidental contact with body parts or to prevent debris, such as chips, from exiting the machine.
magnetic flux A measure of the strength of the field formed around a magnet. Flux is expressed in webers (Wb).
magnetic induction The use of magnets to cause voltage in a conductor. Magnetic induction occurs whenever a conductor passes through magnetic lines of flux.
mechanical power variables The properties of mechanical energy that vary for specific machines and applications. Speed, torque, and horsepower are the three main mechanical power variables for motors.
motor A machine that converts one form of energy, such as electricity, into mechanical energy or motion.
multispeed motor A type of AC motor designed with windings that may be reconnected to form different numbers of poles. This is done as a method of speed control.
percent slip The difference between a motor's synchronous speed and its speed at full load. Percent slip is a way to measure the speed performance of an induction motor.
personal protective equipment Any example of various safety equipment that workers wear or use to prevent injury in the workplace. Safety glasses are common personal protective equipment (PPE).
polarity Having two oppositely charged poles, one positive and one negative. Polarity determines the direction in which current tends to flow.
pole piece Devices mounted on the inside of a motor armature. When connected to field windings, the pole pieces form the electromagnets that create lines of flux.
pound-feet In the English system, the unit used to measure torque.
prime mover The device that introduces motion into a system. In electric motors, electricity is the prime mover that provides the turning force converted into mechanical energy.
revolutions per minute A unit of measurement, abbreviated as rpm, that indicates the number of revolutions a machine component makes in one minute. Revolutions per minute is a measurement of speed.
right-hand motor rule The relationship between the factors involved in determining the movement of a conductor in a magnetic field. This rule helps us understand how motors use magnetic flux to create motor torque.
rotor The rotating part of a motor.
series field A winding of large wire and few turns designed to be connected in series with the armature of a DC motor or generator.
series motor A method of connecting field windings in series with the armature. A DC series motor provides very high start-up torque but must never be run without a load.
shunt field A winding of small wire and many turns designed to be connected in parallel with the armature of a DC motor or generator.
shunt motor A method of connecting field windings in parallel with the armature. The shunt DC motor is commonly used because of its excellent speed regulation.
speed The amount of distance an object travels in a given period of time. Speed is used to measure both linear and rotational movement.
speed control The external means of varying the speed of a motor under any type of load.
speed regulation The ability of a motor to maintain its speed when a load is applied. A motor's speed regulation is fixed based on its design.
squirrel cage induction motor A type of three phase AC motor whose rotor is constructed by connecting metal bars together at each end. It is the most common AC motor type.
stator The stationary windings of a motor, usually inside an AC motor.
synchronous motor A constant speed AC motor that does not use induction to operate. A synchronous motor needs DC excitation to operate.
synchronous speed The speed of the rotating magnetic field of an AC induction motor.
three-phase motor A motor with a continuous series of three overlapping AC cycles offset by 120 degrees. Three-phase power is used for all large AC motors and is the standard power supply that enters homes and factories.
torque A force that produces rotation. Torque is measured in pound-feet in the English system and Newton-meters in the metric system.
watt A unit used to measure power. One horsepower is equal to 746 watts.
weber A unit used to express flux density. One weber (Wb) is equal to 100 million lines of flux.
work The result of a force applied to an object and the distance through which the force is applied. In an electrical sense, work is the result of electricity flowing through some type of resistance.
wound rotor induction motor A three phase motor containing a rotor with windings and slip rings. This motor type permits control of rotor current by connecting external resistance in series with the rotor windings.