Risk Assessment of DC Bias in Multi DC Projects Under Different Operating Conditions

With the continuous expansion of the power grid, large-scale AC/DC hybrid transmission systems are currently facing greater pressure on DC exceeding the standard. By collecting historical operating data of various DC grounding electrodes in Central China, this paper determines the possible operating conditions of multiple DC grounding electrodes, proposes equivalent models for substations and transmission lines, and establishes a DC current model for Central China power grid. Based on the developed DC bias simulation software, the ground potential, grounding current, and DC bias current of substations near the grounding electrode under different operating conditions are calculated. The study found that the impact of the combined action of multiple DC projects on DC bias in substations can be equivalent to the vector superposition of the respective effects of a single DC ground electrode. When multiple DC ground electrodes with the same polarity operate in a relatively close monopolar earth loop, it may further exacerbate the DC bias risk in nearby substations. The research conclusions can provide a reference for DC bias risk assessment and management in areas where multiple DC projects are located.