Sequential Tripping Strategy for a Transmission Network Back-Up Protection Expert System

This paper describes a sequential tripping strategy used in a wide area back-up protection expert system (BPES) to combat situations in which protection relays have maloperated or information is missing. The BPES is an innovative back-up protection scheme designed to prevent the occurrence of widespread blackouts. The BPES evaluates the certainty that transmission lines are likely to be affected by the fault and uses a sequential tripping strategy to isolate the fault if a firm decision is not available due to maloperated relays and/or missing information. The mode of analysis and the sequential tripping strategy ensure that the BPES will clear a fault at minimum risk to the network. An example is included to demonstrate how the certainty factor-based sequential tripping strategy is employed by the BPES to clear a fault that occurred on the southwestern part of the UK National Grid System.