This achievement belongs to the technical field of power transmission and distribution engineering. In the event of system debugging, maintenance or failure, the DC transmission system will adopt a short-term single and large-scale ground loop operation mode. When a single maximum earth loop is in operation, underground DC current will be generated in the soil within a certain range around the DC grounding electrode. In addition, domestic and foreign studies have shown that solar magnetic storms and urban underground rail transit can also generate direct current in the ground. Direct current in the ground will have a greater impact on the AC power grid and the environment within the range flowing through, such as increasing transformer noise, intensifying vibration, and local overheating; changes in the characteristics of transformer equipment, etc., and may also cause harmonic distortion of the AC power grid. Increase; more serious, it may even cause malfunction of power grid protection or equipment damage, seriously endangering the safe and stable operation of the urban power grid. In addition, ground current will also cause a certain degree of interference to some precision electronic measurement equipment, and the long-term impact of ground current may also cause damage to surrounding buried facilities.  Based on the needs of comprehensive management of groundwater currents in the Yangtze River Delta region, the project has completed a total of 13 related subject research and engineering special work in the past 10 years. It has mastered the impact of groundwater DC current on power grids and equipment, and has overcome the regional groundwater current distribution calculation technology., carried out the management of DC bias impact of regional power grids, and established a regional DC bias management management system and technical system. The main innovative results are as follows: 1. In order to overcome the problems of complex modeling and low calculation efficiency, a regional earth resistance network based on finite element analysis was first created. Combined with the power grid resistance network, a calculation model of the ground DC current of the regional power grid can be built, which can accurately calculate the ground DC current distribution under conditions of multiple DC landing points and multiple operating conditions of the regional power grid. 2. Aiming at the problem that transformer differential protection is prone to malfunction under DC bias, a new principle of transformer differential protection based on phase-by-phase blocking is proposed for the first time to ensure the correct operation of transformer differential protection under DC bias and ensure primary equipment safety. 3. In order to ensure the orderly management of regional DC bias and avoid duplication of construction and waste of resources, a regional DC bias management plan was proposed, and based on a large amount of engineering practical experience, a technical standard system covering planning and design, equipment manufacturing, and power grid operation was established., a full-process management system with the participation of multiple departments such as planning, infrastructure, production, and dispatching of multi-level power grids, and took the lead in formulating China's first IEC international technical specification in the field of transformers: IEC TS 60076-23 "Power transformers: DC bias suppression devices".  This achievement has made breakthroughs in key technologies such as DC bias impact analysis and evaluation, monitoring and early warning, engineering governance and technical management. A total of 6 invention patents and 15 utility model patents have been authorized, and 6 papers have been published, including 3 SCI papers; Compiled 1 IEC standard, 1 national standard approval draft, 2 industry standards, and 1 enterprise standard. The results have been applied in 49 substations in East China, Liaoning, and Mengdong, effectively solving the impact of DC bias on the AC system, providing strong technical support for the promotion of DC transmission technology, and has broad prospects.