Tom Bishop, P.E.
EASA Technical Support Specialist
 
Prior to rewinding it is advisable to assess the condition of the core iron of stators, armatures and wound rotors. The assessment is performed by a core test, which magnetizes the core to a pre­scribed magnetic flux density. The predominant tests used to determine core condition are the hot spot test and the core loss watts test. The hot spot test compares the hottest spot in the core to either ambient temperature or core average temperature. The watts loss test compares the core loss test watts prior to winding removal to the same test af­ter the windings have been removed and the core prepared for rewind. 

Core testing traditionally was performed by the use of the loop (ring) test. That required multiple turns of wire to be passed through a core in order to magnetize the core and test for shorted laminations. Mag­netic strength is related to the ampere-turns (amperes x turns) of the magnetizing coil. Mod­ern core testers make it possible to test a core with a single turn of wire, by using high current. Thus the core tester uses one turn and many amperes, whereas the loop test typically uses many turns and a relatively low current. 

Categories: AC motors, Service center equipment, Testing, Motor testing

Tags: Core loss testing

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