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Energy Efficiency Reference Guide Electric Motors

2 Motor Classification

An electric motor is a device which converts electrical energy into kinetic energy (i.e. motion).

Most motors described in this guide spin on an axis, but there are also specialty motors that move linearly. All motors are either alternating current (AC) or direct current (DC), but a few can operate on both (See Figure 2-1). The following lists the most common motors in use today. Each motor type has unique characteristics that make it suitable to particular applications.

Figure 2-1: Motor Family Tree

Figure 2-1: Motor Family Tree

Alternating Current (AC) Motors

AC motors include 3-phase and single phase types.

3-phase AC induction motors are the most widely used motors in industrial and commercial applications. They are divided into two sub-categories:

  • Squirrel cage motors
  • Wound rotor motors

3-phase Synchronous motors are most commonly used in very large industrial applications or where exact speed is required.

Single phase induction motors are used where three phase power is not available; typically in residential, commercial and agricultural applications. They are also used in applications with power requirements below 1 horsepower (HP). The main sub-categories include:

  • Split phase
  • Capacitor run
  • Capacitor start
  • Capacitor start - capacitor run
  • Shaded pole
  • Universal motors

Universal motors are mostly operated on AC power, but they can operate on either AC or DC. Tools and appliances are among the most frequent applications.

DC motors are often used in applications where precise speed control is required. They are divided into three sub-categories:

  • Series
  • Shunt
  • Compound

Advanced motors have been developed in recent years, a number of which do not neatly fall within traditional motor classifications. They are typically used in OEM applications. Examples include:

  • Electronically commutated motors
  • Switched reluctance

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