No abstract

The advantages of using flexible AC transmission system devices increase the penetration of these devices in the existing power systems, but it is necessary to reconsider the protection schemes of a compensated network. This paper investigates four conventional schemes of loss of excitation (LOE) protection, which is used in the commercial relays, in the presence of Unified Power Flow Controller (UPFC) by both analytical and simulation approaches. The first scheme is based on the capability curve of the synchronous generator. The second scheme is the admittance-based method. The third scheme uses two double circled diagrams with a negative offset. The fourth scheme uses doubled circle diagram with a positive offset and directional element. This paper compares and evaluates the performance of these schemes in precise detail. In addition to LOE, the impact of partial loss of excitation, external fault and power swing on the LOE relay in the presence of UPFC is investigated.