Scheme of simultaneous AC-DC power transmission in medium voltage distribution network

With rapid growth of demand for electric power for high-speed development of national economy and the introduction of New Energy Resource, especially in big city, the construction of new transmission lines is of great urgency. But the project is restricted by the shortage of transmission corridor. This drawback limited the transmission capacity between power plant and load center by present AC power transmission system. Based on zigzag transformer, this paper presents a simultaneous AC-DC power transmission scheme, a new circuit topology, in medium voltage distribution network by superimposing dc power flow on existing AC line. The mixed AC and DC circuit and composited voltage is regulated below thermal limits and the insulation level of the line respectively. No alterations of conductors, insulator strings, breakers and towers of the original line are needed. As circuit is closed to the conductor´s thermal limits in the AC-DC system, the transmission capacity of distribution line is significantly improved. In this paper, the performance and advantage of zigzag transformer is elaborated. Scheme of simultaneous AC-DC power transmission system applied in medium distribution network is put forward and the maximum of the total power transmitted by the system is analyzed theoretically and numerically. Simulation is also supplied.