防止超高压备自投诱发线路零序过流保护误动的对策初探

高压内置型高阻抗变压器空载合闸时可能会产生高幅值的零序涌流,该零序电流在上游线路中分配后很可能引起线路零序过流保护误动作。这一现象同样存在于变压器备自投过程中,从而导致备自投失败。为解决这一问题,首先从零序涌流特征出发,结合零序涌流的半解析表达式,量化分析零序涌流中间断角和二次谐波含量特征,并据此分析利用传统的间断角和二次谐波涌流识别判据进行零序涌流辨识的可行性。理论分析表明:较相涌流,零序涌流的间断角显著减小,不适用于涌流识别;二次谐波特征显著加强,可作为识别零序涌流的可取方案引入零序过流保护,保证变压器备自投正常进行。最后,基于PSCAD/EMTDC的仿真结果验证了上述结论的正确性。

Study on countermeasures to prevent maloperation of zero-sequence overcurrent protection caused by ultra-high-voltage automatic device transfer

There may be high-amplitude zero-sequence inrush generated by a high voltage built-in high-impedance transformer in the process of no-load closing.The zero-sequence inrush will distribute in the line and may cause the maloperation of the line zero-sequence over current protection.In addition,the above phenomenon exists when a spare transformer is put into operation,and the automatic device transfer operates unsuccessfully.In order to solve this problem,the characteristics of zero-sequence inrush are studied based on the formula of zero-sequence inrush in this paper.The dead angle and second harmonic of zero-sequence inrush are calculated and analyzed.On this basis,the feasibility of a dead angle and second harmonic breaking criterion to identify zero-sequence inrush is analyzed.The results show that the dead angle of zero-sequence inrush reduces so significantly compared with phase inrush that it cannot be regarded as a characteristic to identify zero-sequence inrush.The second harmonic component increases obviously,so the second harmonic breaking criterion is an advisable scheme to ensure that automatic device transfer is put into operation successfully.Finally,a simulation test based on PSCAD/EMTDC verifies the accuracy of the analysis results.