Pilot Protection Based on Cotangent Similarity for Transmission Line with Renewable Energy Sources Connected

Abstract

With the high proportion of renewable energy sources (RESs) connected to the power grid, the short-circuit current characteristics are altered by the RESs. It may lead to mal-operation of the conventional pilot differential protection. To solve this problem, the differences in fault current characteristics between the RESs and the traditional generators are analyzed. Further, a new novel protection scheme is proposed based on cotangent similarity. The principle of cotangent similarity is introduced in order to differentiate the fault current waveforms between the RESs and the traditional generators. Compared with the protection strategy based on the cosine similarity, the proposed protection algorithms can correctly distinguish the internal or external faults even when the short-circuit current contributed by RESs is zero. Finally, the simulation tests were carried out based on PSCAD/EMTDC. The test results show that the proposed protection scheme is effective for the power grid connected with the RESs.