Features: 1) In order to avoid serious failure happen in distribution power network, especially in the network where lot of ring main unit load switches were used, as a rule, the upper level system must trip within the time setting when a short circuit or earth fault occurs in the lower level 2) After breaking, the whole network subjected to the upper level will be power outage 3) The indicator is used to locate and indicate the fault position, then the maintenance personnel can find and trip the fault section quickly based on its signaling information 4) It will reduce the time and narrow the range of power outage