Locating voltage sag source with impedance measurement

Voltage sag is one of the major power quality problems that maybe result from networks fault and sudden increase of the load. It will result in abnormal operation or shutting down of device. Sag location is an important topic because power-quality trouble-shooting, diagnosis, mitigation policy could be constituted and mitigation measurement be carried out only after locating the voltage sag source accurately. A method based on the impedance measurement in dq0 coordinate system is proposed in this paper. Firstly, the three-phase voltage and current measured at the monitoring point are transformed by the orthogonal Park's transformation. And then the certain character of obtained three-phase instantaneous impedance measurement is used to locate the sources of the voltage sags. Constant impedance load and induction-motor load are used in digital simulation respectively. The simulation results show that the method can locate the disturbance source whether symmetrical or asymmetrical happens.