Electrical Motors and Heat Loss

Percentage of losses in an induction motor according to California Energy Commission Report January 2003

1. Stator core Losses = 38 %

2. Rotor Core Losses=22%

3. Core Losses =20 %

4. W & F Losses= 8%

5. Stray Losses =12 %

I think #3 is more commonly referred to (collectively) as "iron losses", being the combination of magnetic hysteresis and eddy currents in the laminations. #1 and #2 are sometimes collectively referred to as "I²R" losses, or resistance losses, and represent the majority of the heat output of a motor into the surrounding environment. The other heat producing element is friction and to a tiny extent, windage (the W & F above).

So to accurately determine the heat output, you must first determine the motor's efficiency rating, then use the above percentages as the portion of that inefficiency that is creating heat. many tables such as the one above are now outdated because they are based on older motor designs. Newer Energy Efficient motors, required in many areas, are significantly more efficient than that. For example it used to be common to assume 70% efficiency in mid-sized motors, now it is closer to 95%.

Example: 100HP motor, 74.6kW at 70% efficiency = 22.38kW in losses, of which 60% will result in heat output, so 13.4kW in heat.

Same motor, 95% efficiency rating = 3.73kW in losses, of which 60% is heat = 2.38kW. That's a BIG difference!

Example of Losses Calculation

http://cr4.globalspec.com/thread/62748/Induction-Motor-Impedence