Fiberoptic SCADA system safeguards underground distribution network

A network improvement program for improving the safety and operation of the Pacific Gas & Electric Company (PG&E) network distribution system is described. The program had three objectives: to prevent total network shutdown from secondary fault; to prevent a catastrophic failure in a building vault; and to minimize damage to customer and PG&E facilities. The supervisory control and data acquisition (SCADA) system monitors 500 remote terminal units (RTUs) in San Francisco and 150 RTUs in Oakland. The information includes: protector status, protector heat sensor, transformer temperature, vault temperature, vault water level, three-phase secondary current, and transformer sudden pressure relay. A fiber-optic communications system was chosen because it does not require trenching, is nonconductive, and is immune to electromagnetic and radio interference. The fiber-optic equivalent of a telephone cable repeater system with a repeater placed at each RTU location was used. The fiber-optic transceiver design is described, and cable requirements and vault installation are discussed. The RTU communications scheme is identified, and operating experiences are reported.<>