A Current Transformer Saturation Countermeasure Study For Transmission Line Current Differential Protection

Current differential protection principle is simple and reliable, high sensitivity, operation fast, and with the natural features of the election, the Current differential protection has been widely used to HV and UHV transmission line as one of the main protections. However, current transformer (CT) saturation is still affecting the reliability of transmission line differential protection. Especially at external fault it will case misoperation of current differential protection. So how to solve the current differential misprotection cased by CT saturation is a subject that has been exploring.The paper has studied on the effects of current differential protection on the transmission line that cased by CT saturation. Simulation through the analysis of specific models of several factors on the impact of CT saturation, and then analyse the CT saturation detection methods of the status quo, based on improvement gradient form of mathematical morphology, the CT saturation detection algorithm is proposed. The appropriate kind and length of the structural elements is proposed by Simulation Test, so the improved algorithm has a superior de-noising ability and capacity of singularity detection. The algorithm can effectively detect the time when the CT core is saturated and the fault time. then the Comparative simulation tests are completed when the CT second current in the noise-free dry and noise, The simulation results indicate that the improved algorithm is correct and effective.Due to the time difference method is simple and effective ,can effectively detect the CT saturation when the external faults occur, and the improved morphological gradient algorithm can effectively calculated the time difference.this paper Proposed transmission line current differential protection program against CT saturation combined with time difference method and improved morphological gradient algorithm.The program can effectively prevent the current differential protection misoperation external at the time of CT saturation, The simulation results clearly indicate that the proposed method is correct and effective.