Optimal Coordination of Distance and Overcurrent Relays with Sparse Placement

For the protection engineer, it is often the case, that full coverage and thus perfect selectivity of the system is not an option for protection devices. This is because perfect selectivity requires protection devices on every line section of the network. Due to cost limitation, relays may not be placed on each branch of a network. Therefore, a method is needed to allow for optimal coordination of relays with sparse relay placement. In this paper, methods for optimal coordination of networks with sparse relay placement introduced in prior work are applied to a system where both overcurrent and distance relays are present. Additionally, a method for defining primary (Zone 1) and secondary (Zone 2) protection zones for the distance relays in such a sparse system is proposed. The proposed method is applied to the IEEE 123-bus test case. The proposed method is found to successfully coordinate the system while also limiting the maximum relay operating time to 1.78s which approaches the theoretical lower bound of 1.75s.