Relative location of voltage sags source at the point of common coupling of constant power loads in distribution systems

Constant power (Scte) loads such as large induction motors or power converters in customer facilities of distribution systems have a significant effect on the fault currents and thus on the relative location of voltage sag sources. This paper evaluates the methods for determining the relative location of voltage sag sources at the point of common coupling (PCC) of Scte loads. The results of simulating 800 voltage sag events on IEEE 13 bus unbalance system (modelled by ATP) show that many of the methods fail at classifying upstream (US) faults at the PCC of Scte loads. Therefore, a new method is introduced using the ratio of current magnitudes and changes of power angle in positive sequence components, during and before the voltage sag, with a determined threshold for the currents and a specified tolerance for the power angle obtained from voltage sags generated by different fault types. The results obtained in the proposed index for similar simulation cases show that the method applied to monitors installed at the PCC of the Scte loads is very accurate. Also, the proposed index is effective for higher resistance faults and changes in the short circuit capacity (SCC) of the main grid.