A branch-based method to break-point determination for coordination of over-current and distance relays

Modern power systems have a multiloop structure. Coordination of distance and over-current relays in these networks is a tedious and time consuming task. The most complicated part of this problem is determination of break-point set (BPS) to start relays setting. As BPS is not unique, it is desirable to determine a BPS with a minimum or near to minimum number of members. This paper presents a new BPS determination method based on the network branches. Two lemmas are presented to simplify the network. Application of these lemmas splits the network into some reduced subnetworks, if possible. This reduces the problem dimension and computational burden. This method is so simple it even can be applied on a network manually. Moreover, this method has the capability of considering the three-end branches such as three-terminal transmission lines and three-winding transformers, which graph theory based methods can not handle these cases. The validity of the new method has been tested for an Iranian network.