Influence of the structure of transmission line on harmonics distribution in DC system

The transmission distance of DC project is always long, and along the transmission distance, the structure of lines and towers varies according to local environment. It is hard to build a precise harmonic model composed of different sections of line with exact line parameters, so it is important to research the influence of line structure on the harmonic distribution in system and find the key parameters, in order to simplify the model. By building models of different line parameters in harmonic analysis program and calculating, it is found that the line spacing has a strong influence, the influence of height weakens when higher, the earth resistivity, ground wires and conductor type affect little, but the bundle number and spacing affect a lot, especially at low frequency. The influence rules on filter equipment are the same. The EMTPC simulation verified these conclusions. Combined with the practical project design convention, the height is the most important subsection basis. It is verified that a simplified model of a few line sections of different parameters can simulate the harmonics in project exactly.