Influence of AC and DC lines erected on the same tower on the electrical characteristics of DC system under steady-state operation

Faced with the rapid increase of power demand in load center and the shortage of transmission corridor, it is urgent to explore the possibility of erecting UHV/HVDC transmission lines and AC transmission lines on the same tower. Therefore, based on the topology and parameters of a ± 800kV UHVDC transmission project, this paper builds a model in PSCAD/EMTDC electromagnetic transient simulation software to study and analyze the influence of six influencing factors on the AC/DC electrical characteristics on the same tower during steady-state operation. The simulation results show that the AC and DC lines erected on the same tower have significant influence on the DC current of the converter transformer, but have little influence on the equivalent interference current in the DC line and the harmonic distortion rate of the AC bus voltage at the converter station. The factors, such as the length of the same tower section, the participation of the grounding electrode in the same tower, the transmission capacity of the AC system and the operation mode of the AC system have great influence on the DC current in the converter transformer. On the whole, new requirements will be put forward for the DC current of converter transformer. The engineering design requirements can be met from optimizing protective measures and improving the electrical indices of equipment.