Setting Calculation of the Directional Relays Considering Dynamic Changes in the Network Topology

Identifying some typical and critical system conditions is an important and key step in conducting setting calculation of the directional relays. Under these normal operation or contingency conditions, fault calculation is performed to determine the suitable settings or check relay performance such that their fundamental protective objectives are met for a variety of system configurations and conditions. This paper analyzes the impact of dynamic change of network topology on the relay setting, which includes line outages, breaking of loops and operation mode switching of power substations or plants. Electrical coupling indices of loops are introduced to determine the break-loop lines, whose outage will result in great impact on the distribution of fault current. In addition, sensitivity factors are derived for determining the substations or plants and their corresponding operation modes which have the greatest potential impact on the fault current magnitude. Examples are presented to verify the validity and simplicity of the proposed methods.