Prediction of the Operational Impedance of Rotating Machines by Various DC Testing Methods

This paper presents methods to determine the operational impedance of rotating machines by Fourier Transformation of the voltage and current measured when a step (or pulse) voltage is applied to the two stator winding terminals. These standstill tests using a small-capacity DC power supply unit are tentatively named the DC Testing Method. We also describe in detail the case using a DC power source with ripple and the case in which a step (or pulse) voltage is applied with current flowing. These methods are applied to a 5.5kW squirrel-cage induction motor having semi-closed rotor slots. The validity of the proposed prediction methods is demonstrated by comparing the calculated and measured speed characteristics of the tested induction machine.