Research on Neutral Grounding Mode of Interconnecting Transformer in Renewable Energy Plant

With the increasing number of renewable energy plants connected to the power system, the gap grounding mode is often adopted by the high-voltage side neutral point of the interconnecting transformer of the renewable energy plants in order to improve the performance of the zero sequence protection. In practical engineering applications, the low-voltage side of the interconnecting transformer is connected with the renewable energy source (RES). It is necessary to analyze and evaluate the possible overvoltage at the high-voltage side neutral point when the power grid fails, as well as the damage brought to the stable operation of power grid. According to the operation characteristics of RES, the calculation method of neutral point overvoltage is proposed and the influence of different types of RES on neutral point overvoltage is analyzed when a single-phase grounding fault or a single-phase break-line fault (incomplete phase operation state) occurs in the power grid. Then the suggestions to prevent neutral overvoltage are proposed. The correctness of correlation analysis is verified by digital simulation and the conclusion can provide an important reference for the reasonable choice of the neutral grounding mode of the interconnecting transformer in renewable energy plant.