A Study of the Effect of Phase Shifting Transformers on Line Longitudinal Differential Protection

For the problem of uneven power flow distribution and line overloading in the power grid, symmetrical double-core phase shifting transformer (PST) can be used to realise the control of line power flow. Due to the symmetrical double-core phase shifting transformer access to the equivalent impedance and voltage shift angle of the impact of the line longitudinal differential protection may be false or refused to act, resulting in the protection can not be correctly acted. Based on the structure and equivalent circuit of symmetrical double-core phase shifter transformer, this paper analyses the influence of its access on the power flow distribution of the power system and the influence mechanism on the longitudinal current differential protection, and puts forward the improvement measures for the longitudinal current differential protection of the line containing phase shifter transformer. Finally, a simulation model is constructed in PSCAD, and simulation is used to verify the correctness of the mechanism analysis and the effectiveness of the proposed improvement measures.