HVDC Interference to Buried Pipeline: Numerical Modeling and Continuous P/S Potential Monitoring

Wuxi, Bi (Petrochina Pipeline Company) | Hongyuan, Chen (Petrochina Pipeline Company) | Zhenjun, Li (Petrochina Western Pipeline Company) | Youwen, Jiang (Petrochina Pipeline Company) | Lingli, Liu (Petrochina Pipeline Company) | Yabo, Hu (Petrochina Pipeline Company)


Abstract As one of the most important ways for long-distance transmission of electricity, High Voltage Direct Current (HVDC) transmission lines in China are developing very fast. In some regions, HVDC interference to pipeline becomes a main threat to pipeline safety. Based on a realistic HVDC interference project, Hami South to Zhengzhou ±800kV HVDC transmission line, numerical modeling tool was used to analyze the impact of running of the Hami South grounding with 5000A mono-polar current flowing to the HVDC grounding. This numerical assessment was performed before the HVDC project was put into use. The results show Hami South grounding will cause interference problem to the nearest pipeline, which is 35km far away: the most positive P/S potential should be around +0.65V vs Copper/Copper Sulfate Electrode(CSE) due to poor soil conductivity. Five months later, the HVDC was put into use. Meanwhile, continuous P/S potential monitoring devices were installed on the potentially interfered pipeline section. The most positive P/S potential from monitoring devices was proven to be about +0.50V (CSE). The interference intensity from numerical modeling+0.65V (CSE) meets the field monitoring result +0.50V (CSE) very well, which proves the necessity of numerical modeling in deal with HVDC interference related problems. Moreover, 5 and 7 mitigating cathodic protection (CP)stations, with recommended working current outputs, were evaluated by numerical modeling tool. Background High Voltage Direct Current (HVDC) is an economical way to transport electrical power over long-distance. Now there are more than 10 HVDC transmission lines in service in China, and the number is expect to be doubled in next 10 years. During the past years, HVDC interference to pipelines nearby has become a serious problem in some regions of China. HVDC transmission line shave two distinct running modes: bipolar mode and monopolar mode. Under normal running condition, HVDC transmission line use bipolar mode, with two metallic phase lines, one for positive phase and the other for negative phase. It is widely believed that bipolar HVDC running mode has very little influence on pipelines because of relatively static DC transmission current in line. But unavoidably, HVDC transmission lines have to use monopolar mode during routine phase line repair time and emergency fault conditions. When running under mono-polar mode, a HVDC transmission line will use earth as the other DC phase, which may result in serious DC interference to the pipelines near to the HVDC ground electrode.

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