Fault isolation - no voltage sensor

A method for locating and isolating a fault in a power distribution network, the network including at least one power source, at least one feeder and a plurality of switching devices positioned along the at least one feeder and being in communications with each other, where network sections are defined between adjacent switching devices and where at least one of the switching devices does not have a voltage sensing capability, the method comprising:

• detecting an overcurrent event in the network from the fault by at least some of the switching devices;
• interrupting the overcurrent event by opening and then immediately locking out or performing subsequent reclosing operations by at least one of the switching devices that detected the overcurrent event;
• increasing a count value in the switching device that interrupted the overcurrent event and in each of the switching devices that detected the overcurrent event and then detected loss of voltage upstream, in each of the switching devices that detected the overcurrent event and does not have a voltage sensing capability and in each of the switching devices that detected the overcurrent event, does not have a voltage sensing capability and inferred the loss of voltage upstream by measured current;
• sending a count and current (C&I) message from each of the switching devices that detected the overcurrent event and then measured the loss of voltage upstream, from each of the switching devices that detected the overcurrent event and has an upstream neighbor switching device that does not have a voltage sensing capability, from each of the switching devices that detected the overcurrent event and does not have a voltage detecting capability, and from each of the switching devices that detected the overcurrent event, does not have a voltage detecting capability and inferred loss of voltage upstream by measured current, the C&I message including the locally measured current by the sending switching device and the count value of the sending switching device;
• starting a C&I timer in each switching device that sent a C&I message;
• performing a current matching test, in each switching device that started the C&I timer and it has expired, between the measured current that may have been received in a C&I message by that switching device and current measured by that switching device;
• populating a fault isolation table in each switching device that detects the overcurrent event that includes its count value, its measured current and accumulated current from a received C&I message;
• repeating interrupting the overcurrent event, increasing the count value, sending the C&I messages, starting the C&I timer, performing the current matching test and populating the fault isolation table;
• determining that the fault is in an immediate downstream section of a switching device based on the count value in that device matching a predetermined first count value and a current matching test failure;
• and
• sending a downstream switch open message to an immediate downstream switching device from the switching device that determined that the fault is in its immediate downstream section to isolate a downstream end of the faulted section.