Estimation of the induction machine parameters for simulation of a mixed-frequency test

Mixed-frequency testing of large induction machines is established as a method of causing full-load losses to occur in the machine without the need for a load on the shaft so that temperature rise can be measured. The conventional arrangement for mixed-frequency testing uses a 1.0 p.u. 50 Hz voltage waveform drawn from the main supply on which, typically, a 0.2 p.u. 40 Hz waveform is superimposed using an auxiliary power supply. This paper reports on a convenient set of tests and associated processing of results which can be performed to evaluate the parameters of the induction machine before a suitable mixed-frequency test is performed to determine the full-load temperature rise. The induction machine in this case is driven from a standard inverter which uses PWM to produce a sinusoidal component of voltage whose amplitude and frequency can be modulated by an external function generator