接地极单极大地回路电流运行对天然气管道的影响

Effect of monopolar earth-return operation of grounding electrode on natural gas pipelines

在高压直流输电线路进行调试或发生故障的情况下,直流输电系统采用单极大地回路电流运行方式,接地极有几千安培的电流流入、流出,会对周围金属结构物造成直流杂散电流干扰。以鱼龙岭接地极单极大地回路运行为例,在不同接地极入地电流下,测试受干扰管道不同位置的电位分布和变化,分析广东省天然气管网一期天然气管道的受干扰情况,同时测试采取措施后干扰电位的变化,分析缓解措施的效果。通过电位分析,得到接地极入地电流对管道的影响规律:管道的干扰电位和接地极的入地电流成正比关系;管道受到干扰时,管道极化电位明显超过标准要求,管道存在腐蚀和氢脆的风险,同时绝缘接头位置为风险点;在高压直流输电线路单极大地回路运行时,管道干扰电压达到140.5 V,管道存在人员和设备风险;采用站内接地网作为缓解措施,对连接点位置管道受干扰程度有明显缓解作用,而对远离接地网的连接点位置管道有负面影响作用。

When the monopolar ground-return operation mode is adopted in the high voltage direct current（HVDC） transmission lines during its commissioning and failure, a great amount of current, up to thousands of ampere, flows into and out of the grounding electrodes and consequently brings stray current interference to nearby metallic fabrics. In this paper, the interference on the Phase I natural gas pipelines of Guangdong Natural Gas Grid Co., Ltd. was investigated by measuring the distribution and change of electric potential at different positions of the pipeline under different grounding currents in the monopolar ground-return operation mode of Yulongling grounding electrode. Moreover, the effects of mitigating measures were assessed by analyzing the change of the interference potential. The influential laws of grounding current on pipelines were figured out on the basis of electric current analysis. It is indicated that the interference potential of the pipeline is in proportion to the earth current of the grounding electrode. When the pipeline is under the interference, its polarized potential is beyond the standard remarkably, and consequently it is faced with the risks of corrosion and hydrogen embrittlement and the risk points are located at the insulating joints. In the monopolar ground-return operation mode of HVDC transmission system, the interference voltage on the pipeline is up to 140.5 V, so personnel and equipment are risky. When the station grounding grid is used for mitigation, it has the remarkable effect on weakening the interference on the pipeline only at the connection positions, but the negative effect at the connection positions far from the grounding grid.