In recent years, the air particulate pollutants formed by the combustion of fossil fuels and the emission of industrial waste gases have constantly been produced, and the polluted particles deposit also seriously affects social production and people’s lives. For instance, pollution-induced flashover is seriously threatening the safe operation of the power system, while insulator pollution non-uniformity has great influence on the flashover voltage of insulators. Therefore, in this paper both field contamination experiments of HVDC (High Voltage Direct Current) transmission lines and wind tunnel contamination simulation tests were conducted, and pollution non-uniformity coefficient KT/B, KW/L and KH/M were proposed and obtained. The results showed that the degree of contamination on top surface and leeward side is heavier than that on bottom surface and windward side. Thus, in the DC energized condition, contamination along the string is also non-uniform, and serious pollution occurs mainly in the high voltage terminal. In order to explain the uneven distribution phenomenon along the string, the coupling-physics model of composite insulator string was established and using the finite element method, the electric field around the insulator was simulated. Furthermore, basing on the field charging theory, the value of electric field force on particles around the insulator surface was calculated and the mechanism of non-uniformity along the insulator sting was then explained. The results are very important for guiding insulation design and field anti-pollution works.

Experience shows that under unidirectional wind or certain terrain, the surface of post insulators is non-uniformly polluted between windward and leeward sides, which affects the flashover characteristics. In this paper, a formulation of residual pollution layer resistance was proposed under this non-uniformity and a typical post insulator was taken as an example to analyze and calculate its residual resistance. The theoretical resistance was verified by numerical simulations using COMSOL Multiphysics. The proposed resistance formulation was then implemented in a DC flashover dynamic model to determine the flashover voltage (Ucal), which was validated by artificial flashover tests. Then the factors affecting DC flashover voltage were analyzed. Research results indicate that: the residual resistance formulation agrees well with simulation results, especially when the arc length exceeds 70% of the leakage distance. The good concordance between theoretical and experimental flashover voltages with most relative error within ±10%, validates the flashover model and its residual resistance formulation. Ucal gets impaired under this non-uniformity. The degree of reduction is related to salt deposit density ratio (m) of windward to leeward side and leeward side area proportion (k).