Transient overvoltages and distance protections: Problems and solutions

This paper investigates the relationship between post fault transient overvoltages and the functionality of the numerical distance protection. The study is conducted on a 66 kV network with a neutral earth resistor as method to earth the power system. This paper begins by performing an extensive power system analysis on ground fault transient overvoltages. The study is conducted by using the PSCAD-EMTC software package. The results of this analysis are discussed to determine the impact of a disturbed voltage signal fed to the distance relay, with particular attention to the polarisation and CVT transient mitigation techniques as implemented by modern relays. Finally, this paper provides recommendation for the design of the protection settings of the distance relay. The results of this study show that fault current limitation and consequent reduction of the thermal stress and aging of the equipment are successfully supported by modern distance relays.