Discussion on the Safe Distance Between HVDC Electrode and Pipeline.

The safe distance is an important reference for the mutual avoidance and interference reduction between the pipelines and HVDC electrodes in the planning stage. However, the definition of pipe-to-electrode safe distance in existing standards and researches is still not clear yet. In order to study the reasonable value of safe distance, firstly, the influencing factors of safe distance is analyze through simulation. Soil structure, pipeline length, coating surface resistivity and grounding current are the main factors while electrode type and pipe size are the minor ones. Then, taking touch voltage and DC corrosion rate as the limit respectively, the pipe-to-electrode safe distance is analyzed under different parameter combinations. When touch voltage is taken as the limit, the safe distance to meet the 70V limit is 11km similar to 25km (I = 3000A) and 16km similar to 52km (I = 6000A); The safe distance to meet the 35V limit is 16km similar to 52km (I = 3000A) and 24km similar to 87km (I=6000A). When DC corrosion is taken as the limit, the safe distance to meet the 0.1mm/a limit is 14km similar to 38km (I = 3000A) and 20km similar to 56km (I = 6000A); The safe distance to meet the 0.0254mm/a limit is 32km similar to 65km (I = 3000A) and 44km similar to 70km (I = 6000A); The safe distance to meet the 0.01mm/a limit is 44km similar to 70km (I = 3000A) and 52km similar to 72km (I = 6000A).In order to solve the problems of unknown parameters, uncertain limit standards, and too-large safe distance, the acceptable safe distance is further extracted. The indicator kappa =0.8 is suggested. The acceptable safe distance of 100km short pipeline is 13km (I = 3000A), 19km (I = 6000A) while that of 700km short pipeline is 25km (I = 3000A), 27km (I = 6000A). For the case where the grounding current and pipeline length are also unknown, it is recommended to take the acceptable safe distance of 30km. In addition, the safe distance or acceptable safe distance of long pipelines can be valued according to that of the short ones after segmentation. The acceptable safe distance of 100km short pipelines is 18km.