雷电下直流运行电压对输电线路上行先导起始与发展特性的影响

Influence of DC Operation Voltage on the Initiation and Propagation Characteristics of Upward Leader from Transmission Lines Under Lightning

在分析上行先导发展过程时,许多仿真模型虽在一定程度上考虑了直流运行电压的影响,但其依据主要由棒-板间隙下的试验结果、热力学及电磁学间接外推所得,其适用性并未得到验证。为此,在昆明国家特高压试验基地,就直流运行电压对输电线路上行先导起始与发展特性的影响展开了试验研究。经过仿真分析,设计并采用7m的板棒-导线间隙,并对该间隙施加最高达4MV的200/2 000μs负极性冲击电压,对导线施加最高达800kV的正极性直流运行电压,以此模拟了雷电下的上行先导起始与发展情况。采用最高拍摄速度为1 000 000帧/s的高速摄像机对放电过程的形态进行了观测,同时利用频率响应范围为0～6.5MHz的同轴分流器进行了电流测量。通过数百次试验发现,当线路上施加500kV正极性直流运行电压时,上行先导起始时间提前了21μs,平均发展速度增加了0.3cm/μs,这一结果说明,负极性雷电下较高的正极性直流运行电压有助于导线上行先导的发展。最后,进行了输电线路模拟试验,试验结果说明,负极性雷电下正极性直流运行电压能使导线上行先导的起始时间提前,甚至早于地线;同时正极性直流运行电压也会使导线上行先导的发展速度增加,从而使它对下行先导的截击概率增大,增加了线路绕击的可能性。

When analyzing the propagation process of upward leader, many numerical models take the influence of DC operation voltage （DCOV） into consideration to some extent; however, this consideration is mainly based on the breakdown voltage of rod-conductor gap or theories of thermodynamics and electromagnetism, and lacks direct evidences from actual experiments. Thus, we investigated the influence of DCOV on the initiation and propagation characteristics of upward leader from transmission lines through experiments carried out at the Ultra High Voltage laboratory in Kunming, China. In order to simulate the circumstance for the initiation and propagation of upward leader, a 7 m long air gap which combined plane-rod （PR） electrode with conductor was used. A negative 200/2 000 /~s impulse voltage up to 4 MV and a positive DC voltage up to 800 kV was applied to the electrode and the conductor, respectively. The whole process of upward leader progressing was observed using a high speed camera that had a photographing speed up to 1 000 000 flame/s; meanwhile, a current measuring instrument with its frequency response of 0~6.5 MHz was developed and used to measure the current of leader. According to results of several hundred times of experiments, compared with the conductor in the absence of voltage, the upward leader incepted about 21 /~s earlier and propagated about 0.3 cm//~s faster when 500 kV positive DCOV was applied. The results reveal that positive DCOV is favorable for upward leaders propagating in negative lightning circumstance. Furthermore, the shielding failure process was simulated and tested, and the earlier inception time and faster velocity of upward leader from conductor with DCOV could be found compared with those of the upward leader from ground wire. The results suggest that the striking distance of conductor will increase when a voltage with the opposite polarity of lightning is applied to, leading to easier occurrence of the lightning attachment to transmission conductors and increase in the possibility of shielding failure.