基于纵向阻抗的变压器虚拟相位保护

Transformer virtual phase protection based on longitudinal impedance

针对风电系统中高频元件产生的高次谐波会影响变电站主变保护运行的问题,提出了一种变压器纵向阻抗虚拟相位保护的方法。该方法对故障分量电压平移后两侧的虚拟纵向阻抗求相位差,然后通过PSCAD(power system computer aided design)平台搭建模型进行仿真进行验证。通过对比电压数据链可知:发生内部故障时,虚拟相位差大于90°;发生外部故障时,虚拟相位差小于90°。最后仿真结果表明:在区内故障发生时,虚拟相位差由0°变为180°,远大于90°,保护动作;当发生外部故障以及可能会影响到保护可靠性等因素时,虚拟相位差变化范围仅为0°~20°,远小于90°,保护不动作。故可基于此进行理论分析得出以下结论:内部故障能够可靠动作;在外部故障、电流互感器(current transformer,CT)饱和及励磁涌流产生时,即使有谐波的影响,保护仍不会动作。同时,现有误差精度为10%的CT能够满足此保护方法。仿真结果与理论分析一致,验证了在现有的CT精度下保护的正确性和可靠性以及较好的抗CT衰减能力。

Aimed at the problem that the high harmonics generated by high frequency components in wind power system will affect the operation of substation main transformer protection,a method of transformer longitudinal impedance virtual phase protection is proposed.This method calculated the phase difference of the virtual longitudinal impedance on both sides of the fault component after the voltage translation,and then built a model on the power system computer aided design(PSCAD)platform for simulation and verification.By comparing the voltage data link,it can be seen that when an internal fault occurs,the virtual phase difference is greater than 90°;when an external fault occurs,the virtual phase difference is less than 90°.Finally,the simulation results show that the virtual phase difference changes from 0°to 180°,which is much greater than 90°;when the fault occurs in the area,the protection acts.In case of external fault and other factors that may affect the reliability of protection,the variation range of virtual phase difference is only 0°~20°,far less than 90°,and the protection does not act.Therefore,the following conclusions can be drawn from theoretical analysis:internal faults can operate reliably;In case of external fault,current transformer(CT)saturation and excitation inrush current,the protection does not act even under the influence of harmonics.At the same time,the error accuracy of existing CT can meet this protection method.The simulation results are consistent with the theoretical analysis,and verify the correctness and reliability of the protection under the existing CT accuracy and the better anti CT attenuation capability.