Research on the burial depths of the annular grounding electrodes in UHVDC converter stations

The grounding electrodes of UHVDC power grid can constrain continuously neutral voltage of the converter stations, and protects equipments from damaging as unbalanced voltage. Therefore, it is important to improve the feature of the grounding electrodes. This paper focus on the domestic ±800KV DC annular grounding electrodes features. Based on the equivalent image method, to double annular electrodes buried in uniform soils, the effects depending on the burial depth of the grounding electrodes are analyzed. Through calculating and simulating, the results show that the step voltage and the earth resistance decrease with increasing the depth of the Grounding electrodes, but the temperature of the Grounding Electrodes increases. The project of unequal burying depth of the Grounding Electrodes such as inner being lighter than the outer is proposed, and the best laid proportional range of the inner and outer ring is proposed also. These projects improve grounding features and security to UHVDC power grid, and decrease engineering quantity.