Three phase harmonic modelling of power system loads

This paper reports the development and testing of a method for modelling distribution load impedances as unbalanced three phase impedance matrices for detailed harmonic studies. The experimental testing of this method was performed using data obtained from capacitor switching and transformer tap changing disturbances. This method is applicable even in situations where harmonic sources within the load exist provided that the output of these sources is effectively uncorrelated with the applied disturbance. Computer simulation results gave a measure of the self impedances, accurate to within 5% at the resonant peaks, but gave a considerably less accurate measure of the mutuals. The results obtained from measurements taken at the supply end of a distribution feeder show that the disturbance resulting from a transformer tap change event can give results consistent with those obtained from the much larger capacitor switching disturbance