Improving open-loop medium-voltage feeder self-healing

A common practice for improving electric service reliability is to provide an alternate source of supply. On the distribution system, two feeders-each with one or more mid-line overcurrent protective devices-can be tied together through a normally-open tie point to restore service to unfaulted sections of line. Conventional looped distribution systems rely on overcurrent coordination to ensure that the correct device in the loop clears a given fault. But existing technologies have limited abilities to properly coordinate a large number of devices in series. This paper outlines the application of new technologies that enhance the loop system concept by testing the line for faults without using conventional reclosing. Pulseclosing technology, unlike conventional reclosing, reduces thermal and mechanical stress on substation transformers and other equipment by eliminating the repeated occurrence of high fault currents. It overcomes coordination constraints, allowing the expansion of a distribution loop to an unlimited number of series overcurrent protection devices. Pulseclosing effectively hunts for faults without affecting upstream customers and it reduces the opportunity for sympathetic tripping of nearby devices. Maximum system restoration can be achieved within a few seconds after initial fault detection. These advancements are all achieved without the need for communication between devices. (6 pages)