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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