Under direct current voltage, charged particles in the air are subjected to the force of a constant-direction electric field and are adsorbed onto the surface of insulators. This is the "electrostatic dust collection effect" of direct current. Due to this effect, under the same environmental conditions, the amount of contamination on the surface of DC insulators can be more than double that under AC voltage. As the amount of contamination continues to increase, the insulation level correspondingly decreases, and under certain weather conditions, insulator pollution flashover is prone to occur. Therefore, due to this technical characteristic of DC transmission lines, compared with AC transmission lines, their external insulation characteristics are more complex.
