As an essential important part for HVDC system, the grounding electrode line is providing a grounding channel for unbalanced current, and operating current when HVDC run at ground return operation mode. When string parallel arcing horn gap is breakdown caused by lightning overvoltage impulse, the DC ground current will form a stable arc. Due to DC current can’t periodically cross the zero point like AC current, the DC arc is difficult to extinguish, thereby destroys the insulation of the line and seriously threatens the safety of the HVDC system. The dynamic physical characteristics of the DC arc on arcing horn are significantly different from those of switching device arc, secondary arc, AC fault arc and pantograph-catenary arc. In this paper, the experimental platform for DC arc on arcing horn is built, mechanism of arc column short circuit and arc root jump are studied. This paper further analyses the characteristics and the mechanisms of the arc motion when wind speed and direction, magnetic field and the expansion angle of electrode are varied. Arc root jumping is more likely to occur at the upper electrode. There is a competitive relationship between the arc expansion and the transferring effect. The effect of wind on the arc column is greater than the effect on the arc root. The magnetic field has a significant driving effect on both the arc column and the arc root. The research results provide theoretical support for further probing the mechanism of overvoltage fault and arc fault in the grounding electrode line, the method of DC arc suppression, and the improvement of the arcing horn design.

The grounding electrode line is an important part of the Ultra high voltage direct current (UHVDC) transmission system. It acts as the channel to conduct the unbalanced current and the grounding current.The arcing horn consists of a pair of electrodes installed in parallel at both ends of the insulator string, which provides a discharge channel for the fault current by an air gap to protect the insulators. In this paper, the voltage and current distributions of the arcing horn were studied when the grounding electrode line was struck by lightning. It is found that the current and voltage gradually decrease along the direction from the converter station to the earth electrode. An active arc extinguishing method based on variable resistance for arcing horn was proposed. An electromagnetic transient simulation model of the grounding electrode line is established based on the electrical parameters of a ±800 kV UHVDC transmission system. It is found that the absorbed energy of the arc extinguishing unit needs to be at least 31.2 and 49.6 kJ when the lightning current is 20 and 50kA, respectively. According to the calculation results, the arcing horn with arc extinguishing unit was developed and tested. The test results verifies that the designed arcing horn can meet the requirements of engineering application.