The influence of protective relay schemes on the reliability indices of load points in meshed operated MV networks

Power system protection is increasingly becoming a decentralized practice in the Dutch utility industry. In the past, a few protection engineers were fully occupied with power system relaying from one central place. Today, an increasing number of engineers spend a decreasing number of hours on this. A protection engineer has to calculate the settings of protection relays in new systems and he or she has to revise the coordination of protection devices employed in existing power systems, because of changes in the network topology. Since such reviews are usually laborious, they are carried out relatively infrequently. For this reason, a computer program was developed at the Delft University of Technology to provide a tool for protection system performance analysis. The computer program evaluates different network fault conditions and by using protection relay settings, the isolated load points and their reliability indices can be determined. In this paper, two protection schemes are compared: distance and differential protection schemes