Design and testing of a bus differential protection scheme using partial operating current (POC) algorithm

This paper presents a novel bus differential protection scheme that provides enhanced immunity against mis-operation resulted from current transformer (CT) saturation during close-in external faults and better sensitivity for internal faults. The proposed scheme incorporates a fault discrimination algorithm based on partial operating current (POC) characteristic making the scheme capable of discriminating high current internal and external faults even with CT saturation. A supervision technique based on CT saturation detection is also included in the scheme design to increase the sensitivity of the proposed relaying scheme for very high impedance internal faults. A relay model is built in Matlab platform based on the proposed scheme and the performance is validated using a transmission network simulated in Electromagnetic Transients Program (EMTP) for various fault scenarios. Documented results show the proposed scheme improves the performance in terms of reliability, sensitivity, and selectivity over traditional bus differential schemes.