Protection coordination analysis of closed-loop distribution system

With the utilization of the powerful abilities of new type intelligent electronic devices (IEDs), the configuration of the closed-loop distribution system becomes more flexible. The discussions of pilot relaying system, which include the permissive overreaching transfer trip (POTT) system and the directional comparison blocking (DCB) system, are discussed in this paper. Meanwhile, the hierarchical protection scheme of the closed-loop distribution system is adopted, also including the backup protections of breaker failure protection (BFP) and direct transfer trip (DTT). It is shown that the combination scheme of POTT and DCB is very good, so that the numbers and the duration of the interruptions of supply caused by faults can be reduced to the minimum level. This paper completes the analysis and simulation results of the presented protection scheme for various fault locations.