Mike Howell, PE
EASA Technical Support Specialist

The phase balance test is briefly described in section 4.2.8 of ANSI/EASA AR100-2020. Other names for this test include open stator impedance test, ball test, small rotor test and dummy rotor test. The phase balance test is used in some form by many service centers both as a troubleshooting test and a quality control check before winding treatment. The typical approach is to apply a reduced and balanced three-phase voltage to the stator winding terminals with the rotor removed and then to evaluate the resulting current balance and magnitude. Acceptance criteria differ, but it is a reasonable expectation that the current should be balanced within 10% of the average current.

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