Development of a Substation Digital Protection and Control System Using a Fiber-Optic Local Area Network

This article discusses a newly developed protection and control system for which substation digital protection and control equipment are separately located around the outdoor power apparatus and are linked by an optical LAN. Fig. 1 shows a basic system configuration. The monitoring control, bus protection, and transformer protection subsystems are located independently of each other, and are linked by an optical LAN. An IEEE 802.4 complied token bus is used as the protocol of the optical LAN. An optical fiber data transmission system consisting of optical star couplers is applied for the physical layer. The token bus is provided with a unique synchronous sampling function to make the digital protection and control system more efficient. This function attains synchronous data sampling by maintaining the circulating cycle of the token constant. Fig. 2 shows the principle of this synchronization system. Three related manufacturers each made a prototype of the terminal equipment following a unified standard. These units are linked with each other by an optical LAN. The interoperability of the transmission protocol and protection/control function was successfully confirmed. Following an integral function test, this system has been under a trail use test at TOKYO ELECTRIC POWER COMPANY's 500 kV capacity SHIN-HATANO SUBSTATION. In the test, practicability of the system, such as weatherability and surge withstand capability etc., has been checked.