±800kV直流输电线路雷电绕击与反击的识别方法

Identification of Shielding Failure and Back Striking in UHVDC Transmission Lines

研究±800kV直流输电线路雷电绕击和反击故障的机理,建立了绕击和反击的等值电路模型。分析和仿真表明:若发生反击故障,由于杆塔接地电阻的作用,反击故障将包括雷电流入地和随之而来的塔顶电位(绝对值)骤增造成的绝缘子闪络2个过程,对应地,在这2个过程中零模电流的方向相反,使得故障后瞬间保护安装处零模电压出现正负交替;若发生绕击故障,零模电流只沿一个方向,使保护安装处零模电压在故障后一段时间内呈现单调变化。在绕击与反击故障下于保护安装处所观测的零模电压时域特征存在显著差异,在此基础上,从继电保护的角度出发,提出了一种基于小波变换的特高压直流输电线路雷电绕击与反击故障的识别方法,EMTDC仿真表明该方法能对特高压直流全线雷电绕击与反击故障进行识别,且不受雷电流波形的影响。

In this paper, the mechanisms of back striking and shielding failure in ±800kV UHVDC transmission lines were investigated, and the equivalent circuit models were formed. Analysis and simulations show that there are two processes, lightning current grounding and insulator flashover caused by the increasing voltage of tower, when back striking occurs because of the existence of grounding resistance. The directions of zero modal currents are opposed during two processes, which make zero modal voltage alternately change of positive and negative. Besides there is only one direction of zero modal current when shielding failure occurs, which makes zero modal voltage increases monotonically. Zero modal voltages of the two kinds of surges are quite different in time-domain. According to this feature, from the perspective of protective relaying, an identification method for shielding failure and back striking in ~800kV UHVDC transmission lines based on wavelet transform is presented. All signals can be acquired from high speed protection device. The EMTDC simulation results show that the proposed method can effectively identify shielding failure and back striking in the whole UHVDC transmission lines, and not affected by various wave shapes of lightning current.