Improved service reliability for rural electric customers - innovative auto-restoration following loss of primary source interconnection

Plumas-Sierra Rural Electric Cooperative (PSREC) has two interconnections with large investor-owned electric utilities. Presently, PSREC normally operates solely connected to the Pacific Gas and Electric (PG&E) system via a radially fed line. This connection to PG&E is subject to service interruption for events on the PG&E line or connecting facility. Loss of this PG&E interconnection drops the entire PSREC customer load. An alternative service interconnection is available with Sierra Pacific Power Company (SPPCo) on another part of the system. However, this alternative source does not have the capacity to carry the entire PSREC customer load. In an effort to increase the reliability of PSREC´s service to its customers, future enhancements will allow the system to operate with PG&E and SPPCo in parallel, a project PSREC dubbed Marble Live. In addition, PSREC decided to implement an auto- restoration scheme based on scenarios that require PG&E to interrupt service to the PSREC system. In the case of an event on the PG&E line, PSREC will automatically island its system and execute a series of steps to reconnect to PG&E, should conditions permit, or remain disconnected from PG&E and connect to SPPCo after shedding the appropriate amount of load. This paper describes the system protection and control scheme solution that PSREC incorporated to accomplish a system restoration that satisfies the demands of both PG&E and SPPCo while increasing the reliability of service to PSREC´s customers. Audio tone direct transfer trip equipment, IEC 61850 GSSE, also known as UCA GOOSE, messages among geographically diverse locations, and spread-spectrum radio among directional relays provide communication among substations, while the restoration logic resides in communications processors at each substation. The combination of protection elements and communications equipment initiates selective load shedding and restores power from the- - alternate power source to as many retail customers as possible.