Mike Howell
EASA Technical Support Specialist

Locked-rotor testing of three-phase squirrel cage induction motors is used for design validation and qual­ity control; it also can be a valuable diagnostic tool. But, this testing isn’t a common task for most service centers. Two challenges service centers often face are dynamometer torque capac­ity and test panel electrical capacity. The work-around is usually reduced-voltage testing, which presents another challenge – how to extrapolate the test data to rated voltage with reasonable assurance of accuracy. If the extrapo­lation is too far off, we run the risk of either rejecting a good motor or accept­ing a bad one. 

The purpose of this article isn’t to provide detailed procedures for per­forming locked-rotor tests, but rather to present a practical approach for analyzing the reduced-voltage data us­ing tools that most service centers have access to at their facilities. Additionally, while this article will focus on locked-rotor test data, the methodology used can certainly be extended to other tests where similar conditions and relation­ships exist.

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