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.

I. Introduction

Due to the rapid growth of high-tech industrial park and the installation of commercial & information building, even the temporary interruptions of power supply will result in serious impacts on their cost. Therefore, high reliability of supply is requested by the above customers. The current distribution systems, either radial or normally opened-loop type, can't be satisfied to the increasing demands in the reliability issue. According to statistics, the events in the MV distribution network took place mostly on overhead line. The underground of circuits and the construct of closed-loop type can greatly improve the reliability and quality of supply [1]–[3].