The influence of time coordination method on supply reliability

The inverse definite minimum time lag (IDMTL) overcurrent (OC) and earth fault (EF) protection are the main as well as the backup protection in the industrial power system. They are also responsible for clearing the busbar fault. If the protection system is not properly coordinated, the incorrect sequence of relay operations to clear the busbar fault will result in excessive outage in the industrial supply system. The time coordination method (TCM) can help to solve the protection relay setting coordination problem. It can systematically search out the optimum protection relay settings disregarding the relay operating principles. This paper shows that correct backup protection operations can also improve the supply reliability. The supply reliability influenced by the protection relay operations on the unclear fault is calculated. The results show that the protection relay settings coordinated by TCM in the industrial supply system can achieve higher supply reliability