Analysis of the operation of a distance relay during an unbalanced arc fault and verification by model tests

A fault in a gas-insulated substation (GIS) tank can lead to an unbalanced arc failure depending on the array of electric conductors in the GIS. If such a failure occurs nearby and behind a distance relay for line protection, incorrect operation of the distance relay might result. A short-circuit distance relay measures the impedance vector to a fault point using the bus voltage and the transmission line current of the substation as inputs. When an unbalanced arc failure occurs in a GIS, the voltage inputted to the distance relay becomes unbalanced and the voltage waveform is distorted due to the nonlinearity of the arc resistance. Therefore, the impedance vector measured by the distance relay goes into the second quadrant from the -R axis, which might cause incorrect operation of the distance relay when a fault occurs behind the relay. This paper reports the analysis of the above phenomenon by EMTP simulation and the results of the model tests for distance relay operation by an artificial transmission line