Method for isolating a fault and restoring power in an underground radial loop network using fault interrupting switches

A method for isolating a fault in a 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, wherein source 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 and then opening the first recloser that is delivering power to a first section of the network between the first recloser and the fault;
• starting a timer in the transformer including the normally open switching device in response to detecting loss of voltage when the recloser opens;
• opening the downstream switching device in an upstream transformer in the first section in response to detecting overcurrent and then loss of voltage;
• opening the upstream switching device in a downstream transformer in the first section in response to detecting overcurrent and then loss of voltage;
• closing the recloser that opened;
• detecting voltage on the upstream side of the upstream transformer when the recloser closes and opening the downstream switching device in the upstream transformer in response thereto;
• detecting voltage on the upstream side of the downstream transformer when the downstream switching device closes and closing the upstream switching device in the downstream transformer in response thereto;
• detecting overcurrent downstream of the transformer and locking the downstream switching device of the downstream transformer open in response thereto;
• closing the normally open switching device when the timer expires, detecting overcurrent from an alternate source as a result of the fault and opening the normally open switching device;
• detecting overcurrent and then loss of voltage by the transformers in a second section of the network between the fault and the normally open switching device;
• opening the downstream switching device in an upstream transformer in the second section in response to detecting the overcurrent and then loss of voltage;
• opening the upstream switching device in a downstream transformer in the second section in response to detecting the overcurrent and then loss of voltage;
• closing the normally open switching device;
• detecting voltage on the upstream side of the downstream transformer when the normally closed switching device closes and closing the upstream switching device in the downstream transformer in response thereto;
• detecting voltage on the upstream side of the upstream transformer when the upstream switching device is closed and closing the downstream switching device in the upstream transformer in response thereto;
• and
• detecting the overcurrent in the upstream transformer and locking the downstream switching device of the upstream transformer open in response thereto.

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, the two switching devices closest to the reclosers are designated head end switching devices and one of the switching devices is a normally open switching device, the method comprising:

• starting a first timer in the transformer that detects loss of voltage from the loss of power event and has a head end switching device;
• starting a second timer in the transformer that detects loss of voltage from the loss of power event and has the normally open switching device, where the first timer is shorter in duration than the second timer;
• opening the head end switching device when the first timer expires if the transformer still detects loss of voltage;
• and
• closing the normally open switching device when the second timer expires.