Optimization Method of Key Parameters of Differential Zero-Sequence Current Transformer

With the rapid development of technologies such as new energy and medium voltage grounding methods in modern power systems, the zero-sequence current component in various parts of the power grid has been continuously increasing. This highlights the need for zero-sequence current detection in areas such as small current grounding of distribution network, circulation between new energy equipment, zero-sequence protection, and leakage current of photovoltaic system. There is an urgent need for a zero-sequence current transformer that possesses high measurement accuracy, sensitivity, linearity, and saturation resistance, and can adapt to various complex conditions in the power grid. This paper proposes a differential zero-sequence current transformer and its technical principles, investigates its topology and electromagnetic equivalent model, and analyzes the influence of key parameters on its main indicators. Based on this analysis, this paper proposes a design method for the parameters of the differential zero-sequence current transformer. Finite element simulation is used to model and analyze the proposed technical theory and design method. A product-level prototype was developed and tested on the grid. The test data verified that the transformer exhibits excellent performance in terms of measurement accuracy, sensitivity, linearity, and saturation resistance.