Backup protection scheme for transmission line compensated with UPFC during high impedance faults and dynamic situations

This study presents a backup protection scheme for transmission line compensated with unified power flow controller (UPFC) using power differential protection algorithm. In this scheme, power differential feature is evaluated from the apparent power flow in each phase at the local and remote bus to discriminate between the fault and normal situation. The proposed protection algorithm can be integrated with the conventional distance protection to supervise its operation during stressed conditions. Extensive fault simulation studies have been performed for different types of fault with several conditions and critical dynamic situations/issues such as load encroachment, power swing and high impedance fault (HIF). A 500kV three machines four bus transmission system with UPFC has been used to validate the performance of the proposed scheme using MATLAB software. The test results depict that the proposed scheme is robust against HIF, power swing and load encroachment. It is not affected by the variation in pre-fault power flow angle and synchronisation delay. The proposed scheme has also been tested for current transformer (CT) and coupling capacitor voltage transformer (CCVT) transient error, which brings out the superiority of the scheme.