Determination of a three phase harmonic load model using background harmonic levels

A noninvasive method is described for measuring three phase harmonic load models incorporating harmonic sources for composite power system loads. The method relies upon the presence of a dominant harmonic source close to the load being modelled and constancy of any harmonic sources within the load during the period of measurement. The method is shown to perform quite well in a laboratory test, however it is shown to fail when applied to the modelling of an industrial load due to the unexpected presence within the load of a dominant, time-dependant harmonic source. It is recommended that the method described be restricted to use with loads shown beforehand to satisfy the basic modelling assumptions regarding sources within the load and that invasive techniques be used in cases where these assumptions are violated