Improved directional comparison based algorithm for protection of multi-terminal transmission lines

The difficulties of protecting multi-terminal transmission lines are well known. Here, the authors present a protection method based on directional comparison that incorporates a new method of determining which terminal is nearest to the fault. The method has been extensively tested in simulation and has also been tested in the field. The algorithm described operates in such a way that diagnosis of fault type is based on the evaluation of the current direction at the terminal with the largest voltage change. This terminal, designated the key terminal, is recognized as being electrically nearest to the fault by using voltage information from all line terminals. It is not necessary to calculate any settings