Measured sagged voltages caused by identified power system faults

Results of voltage sag measurements from five identified fault cases are presented in this paper. All the measurements were performed at one 110/20 kV substation on the 20 kV side. One fault was caused by a fallen 110 kV tower and two cases represent fallen trees on a 20 kV medium voltage feeder supplied by the substation in question. Another case concerns a fault, caused by a small animal, that occurred in a neighbouring MV network. The fifth fault case is an example of the most typical fault type, an earth fault in the 20 kV network where the fault itself causes no sagged voltages at low voltage customer locations but the circuit operations pertaining to the fault clearing procedure do. The measurement arrangements are explained and the measurement results of these particular faults are presented. By anlyzing identified faults in this way, understanding of the system performance can be deepened.