Digital communications for power system protection: security, availability, and speed

New channels and digital techniques in communications provide opportunities to advance the speed, security, dependability, and sensitivity of protection. In this paper we show that direct digital communications economically provide several bits in each direction, and these extra bits lead to simpler, and more flexible schemes. Using a 19.2 kbit/second channel, eight bits can be securely communicated every 2 ms, with a worst-case end-to-end delay of 6 ms, including processing latency. Communicating eight bits end-to-end creates opportunities for new protection schemes and for combining traditional schemes to enhance performance. Extremely secure direct transfer tripping can occur in less than 6 ms, when a two message sequence is employed. Direct communications using a simple serial asynchronous bit stream ensures compatibility with a wide variety of communications channels, systems, and test equipment. Channel performance monitoring, including sequence of events, outage duration, and unavailability, provides the measurements of performance required to maintain and improve communications, without periodic testing. System operation is a continuous test of the channel