Chuck Yung
EASA Technical Support Specialist
The procedure for core loss testing of stators is well-defined, but there is not as much information available for special cases like rotors, armatures or high-frequency motors. While the same basic principles apply as for stator testing, frequency is the variable that affects how we should interpret the results.
First, a mini-review is in order. Core losses are comprised of hysteresis and eddy-current losses. Hysteresis losses depend on the grade of steel used and are proportional to the frequency.
Eddy-current losses the edge of each lamination occur at the edge of and vary as the square of the each lamination. frequency. That squared relationship and the fact that they are controlled by the inter-laminar insulation make them critical to the motor’s efficiency. As long as the inter-laminar insulation is viable, these losses are controlled. Shorting of the laminations, whether caused by a rotor drag or from insulation breakdown from excessive burnout temperatures, increases the eddy-current losses. Higher losses result in increased heat and higher magnetizing current.
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