Method for restoring power in an underground radial loop network

A method for restoring power from a loss of power event in a power distribution network where the loss of power event occurs outside of the network, the network including a power line, a plurality of transformers electrically coupled to and being positioned along the power line, a first recloser connected to one end of the power line and a second recloser connected to an opposite end of the power line, each transformer including an upstream switching device and a downstream switching device, wherein power is provided to both ends of the power line through the first and second reclosers and one of the switching devices is a normally open switching device, the method comprising:

• starting an opening timer in each of the transformers that detects loss of voltage in a section of the network between the recloser that loses voltage and the normally open switching device;
• opening the upstream switching devices in each transformer between the recloser and the normally open switching device when its opening timer expires;
• sending a clear to close message from each transformer between the recloser and the normally open switching device to its immediate downstream transformer;
• closing the upstream switching device in each transformer that receives the clear to close message;
• starting a closing timer in the transformer that includes the normally open switching device if it receives the clear to close message;
• and
• closing the normally open switching device when the closing timer expires.

A method for isolating a fault in an underground power distribution network, the network including a power line, a plurality of transformers electrically coupled to and positioned along the power line, a first recloser connected to one end of the power line and a second recloser connected to an opposite end of the power line, each transformer including an upstream switching device and a downstream switching device that share a common control board, wherein power is provided to both ends of the power line through the first and second reclosers and wherein one of the switching devices is a normally open switching device, the method comprising:

• detecting overcurrent in the network from the fault by the first recloser that is delivering power to a section of the network that has the fault;
• interrupting the overcurrent by opening the first recloser;
• detecting the overcurrent and then loss of voltage when the first recloser opens by the transformers that are between the first recloser and the fault in the section;
• detecting loss of voltage when the first recloser opens by the transformers that are between the fault and the transformer including the normally open switching device in the section and starting a first timer in response thereto;
• closing the first recloser, detecting the overcurrent again and opening the first recloser again;
• detecting the overcurrent and then loss of voltage again when the first recloser closes and then opens again by the transformers that are between the first recloser and the fault and in response thereto opening the downstream switching devices that are between the first recloser and the fault and sending a clear to close message on the power line to the immediate upstream transformer by the upstream transformers that are between the first recloser and the fault to close if they detected overcurrent;
• closing the switching devices that detected the overcurrent and received the clear to close message;
• closing the first recloser;
• opening the upstream switching devices in each transformer between the fault and the normally open switching device whose first timer has expired that detected loss of voltage, did not detect the overcurrent and did not receive a clear to close message, wherein the upstream switching device in the transformer having the normally open switching device does not open when its first timer expires even though it detected loss of voltage, did not detect the overcurrent and did not receive a clear to close message;
• sending a clear to close message on the power line from each transformer between the fault and the normally open switching device to its immediate downstream transformer;
• closing the upstream switching device in each transformer that receives the clear to close message;
• starting a second timer in the transformer that includes the normally open switching device if it receives the clear to close message;
• and
• closing the normally open switching device when the second timer expires.