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Fundamentals of AC Motors

Posted by Marc Bekolay on Tue, Mar 01, 2011 @ 10:04 PM

Today I am going to explain some of the terminalogy used in AC motors. 

The rage today is green so let's start with electric motor efficiency.  Efficiency is the percentage of input power that is converted to work.  The higher the efiiciency, the more money you save.

FLA: Full load amps: The amount of current the motor will draw when fully loaded.

Design: A,B,C,D: This references the shape curve.  Design B is the standard industrial duty motor.  Design C is used for hard to start loads.  Design D is designed for high starting torque and are best for low speed apllications like presses, elevator and hoist applications.  Design A are not very common.

Poles:  Number of magnetic poles that appear within when the motor is energized.

  • 2 Poles = 3600
  • 4 Poles = 1800
  • 6 Poles = 1200
  • 8 Poles = 900
  • 10 Poles = 720

Service Factor: Is a multiplier that indicates the amount of overload a motor will handle. Motors with 1.15 service factor can be expected to handle intermittent loads of 15% more than its nameplate horsepower.

Types of Motor Enclosures:

  1. ODP: Open Drip Proof: Cooled by continuous flow of air through the internal parts of the electric motor.  Can handle some dripping water.
  2. TEFC: Totally Enclosed Fan Cooled:  Cooled by an external fan mounted on the motor shaft.  The fan blows the air over the surface of the motor.  TEFC Motors are well suited for dirty, dusty and outdoor applications.
  3. TEAO: Totally Enclosed Air Over: Have no fan and are typically applied in fans and axial fans so they utilize the cooling from the the application
  4. TENV: Totally Enclosed Non-Ventilated:  Utilize the surface area of the electric motor to disapate heat.
  5. Hazardous Location:  There are several variations of hazardous location motor including explosion proof.

These are just some of the terms you need to be familiar with when selecting an electric motor for your application.

Topics: Electric Motors