Scott接线变压器后备距离保护研究

为了满足牵引变压器后备保护的特殊需求，针对Scott接线变压器，构造了一种基于相间电压和相电流后备距离保护。从数学模型出发，讨论了Scott变压器高低压侧之间的电压和电流变换关系，并分析了变压器的等值漏阻抗。理论分析表明，三相-两相变换导致Scott变压器高压侧的相地阻抗和相间阻抗无法直接反映低压侧故障。由于无中性点接地，Scott变压器高压侧无法测得相电压，根据电压关系用相间电压和相电流构成了适用于Scott接线变压器的距离保护。仿真结果表明，基于相间电压和相电流构成的距离保护能够明确区分短路阻抗和负荷阻抗，从而正确动作于故障。

Research on backup distance protection for Scott transformer

To meet the special requirements of traction transformer backup protection, a distance protection based on phase-to-phase voltage and phase current is introduced for Scott transformer. Based on mathematical model, the voltage and current transformation relations between the high and low voltage side of Scott transformer are discussed, as well as its equivalent leakage impedances. The theoretical analysis shows that the transformation of three-phase to two-phase makes phase-to-ground and phase-to-phase impedances cannot directly reflect the fault at low voltage side. There is no neutral point grounded and then no phase voltages available at high voltage side of Scott transformer, so a distance protection by using phase-to-phase voltage and phase current is introduced. The simulation results show that the distance protection can identify the fault impedances from load impedances, so it can correctly operate when faults occur.