A travelling-wave relay for the protection of EHV transmission-lines with teed feeds

Protection of teed feeders using traditional distance schemes has long been acknowledged as being difficult. The relay reach is affected by the current flow at the remote feeds. Distance protection is usually set assuming there is no in-feed from the remote busbars. Any in-feed will reduce the relay reach of a distance scheme. This can be overcome by monitoring the feeder conditions so that relay parameters can be adapted to allow for any in-feed in real-time. It is proposed to use a similar adaptive procedure on a nonunit travelling wave scheme so that it can operate successfully on teed circuits. The reach of the scheme is extended into each leg on the teed circuit so that all internal faults can be identified by the scheme independently of the other relays