High-speed backup scheme for zone 2 of non-pilot distance relays

Distance relays use time-stepped protection zones for coordination purposes. The time delay introduced by zone 2 relays limits the use of these devices for extra high voltage (EHV) applications, since the fast fault clearance requirement is not achieved. Normally, transmission lines are protected by means of intercommunicated protection schemes making use of a dedicated channel in order to overcome that delay; however, this channel is also prone to failure. Hence, it could be really advantageous to provide the line with fast protection coverage without making use of communication channels if a secure enough protection algorithm were developed for this specific purpose. An algorithm that is able to detect remote breaker operation and thus to accelerate the time-delayed zone 2 trip of local relay by monitoring changes in two proposed signals is presented. The algorithm performs adequately in two- and three-terminal lines as it is shown by computer simulation results. It is proposed that this algorithm can be used as a fast backup scheme to protect transmission lines in case main communication channel degrades, fails or is not available.