Control schemes in a solar plant complying with different grid codes modulate the output voltage and current significantly during fault. In this paper, the issue with conventional current differential approaches for the line connecting large solar plant is analyzed and a new protection technique using both end incremental current phasors is proposed. The proposed method uses two criteria to identify the internal faults in such connectivity. The first criterion is based on the ratio of both end incremental phase current phasors and the second one uses the magnitude ratio of positive sequence incremental currents. Both the criteria are adaptive to line terminal currents and complement each other enriching the method applicable for any system condition. Performance of the proposed method is tested for different internal and external fault cases and found to be accurate. The compatibility of the proposed method is also validated using real-time simulator. Comparative assessment with conventional current differential techniques reveals the superiority of the proposed approach.Index Terms-Line differential protection, power system faults, adaptive relaying, solar photovoltaic power plant.Adaptive unit protection for lines connecting large solar plants using incremental current ratio

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Fault current control by solar plant converters introduces different fault characteristics compared to conventional synchronous generator based systems resulting in numerous issues to the available protection methods. In this paper, the issues with conventional distance relaying is analyzed while protecting parallel lines connecting solar plant to grid and a new protection method is proposed using local voltage and current data. The proposed non-unit protection method derives positive sequence reactive powers for both lines for different solar plant operating conditions and uses their difference to ensure correct zone-1 protection. For faults during single circuit operation, the method includes an additional scheme comprising of instantaneous zerosequence overcurrent check and delayed distance relaying to derive correct protection decision. Performance of the proposed non-unit protection method is tested for parallel lines connecting solar plant in a 39-bus test system for different situations using PSCAD/EMTDC simulated data and found to be accurate. Comparative assessment reveals the high reliability of the proposed method.

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