Coordination method for protective devices of closed-loop distribution system

Due to restriction of the coordination time interval (CTI) limit of the time-current characteristic (TCC) based protective devices, and the operating time constraints for protecting the line at the substation, the number of the protective devices in series in one distribution feeder is limited. However nowadays, for the purpose of ensuring the reliability of the power system, one popular way related to smart grid is to connect the current radial distribution system to realize closed-loop operation, which may increase the number of protective devices in series. Consequently, to coordinate all of the devices in one line becomes a very difficult even impossible thing. This paper introduces the coordination theories of the devices based on time-current curve, and proposed a method to get rid of the problem mentioned before. A simulation case is studied and simulated to verify the method.