基于铁磁特性虚拟相位在变压器保护中的研究

Study of Virtual Phase Based on Ferromagnetic Characteristics in Transformer Protection

针对励磁涌流和电流互感器(CT)饱和对变压器差动保护影响的问题,从铁磁特性角度提出变压器虚拟相位保护方法。首先,阐述铁磁磁化特性,通过对应于磁化曲线、磁通、电流和相位的方法,对得出的波形进行谐波含量分析。然后,提出新型的变压器虚拟相位保护的方法:通过求故障分量电压平移后的虚拟纵向阻抗相位差来判断区内外故障。由理论分析可知:当发生外部故障时,虚拟相位差小于90°;当发生内部故障时,虚拟相位差大于90°;当发生外部故障、励磁涌流及CT饱和时,谐波不会使保护动作,内部故障保护能可靠地动作。现有的CT精度能满足要求。搭建模型并仿真后可知:当发生内部故障时,相位差由0°突变到180°附近,保护动作;外部故障、CT饱和及励磁涌流时,相位差范围为0°~30°附近,保护不动作。仿真结果与理论分析一致,验证了方法的正确性。

For the problem of excitation inrush current and current transformer(CT)saturation on transformer differential protection,a virtual phase protection method for transformers is proposed from the perspective of ferromagnetic characteristics.Firstly,the ferromagnetic magnetization characteristics are described,and the resulting waveforms are analyzed for harmonic content by means of the magnetization curves,the magnetic flux,current and phase.Then,a new method of virtual phase protection for transformers is proposed:the fault inside and outside the zone is judged by finding the virtual longitudinal impedance phase difference after the voltage translation of the fault component.According the theoretical analysis,it is known that:when an external fault occurs,the virtual phase difference is less than 90°;when an internal fault occurs,the virtual phase difference is greater than 90°;when an external fault,excitation inrush current and CT saturation occur,the harmonics will not make the protection operate,and the internal fault protection can operate reliably.The existing CT accuracy can meet the requirements.After building the model and simulation,it is known that:when the internal fault occurs,the phase difference changes from sudden 0°to near 180°,and the protection acts;when the external fault,CT saturation and excitation inrush current occurs,the phase difference ranges to near 0°~30°,and the protection does not act.The simulation results are consistent with the theoretical analysis,which verifies the correctness of the method.