EFFECT OF INSULATOR PROFILES ON DC FLASHOVER VOLTAGE UNDER POLLUTED CONDITIONS - A STUDY USING A DYNAMIC ARC MODEL

From field experience and laboratory tests, it has been observed that the contamination flashover voltage of insulators used on dc lines is more influenced by geometry (diameter and profile) than those used on ac lines. Presented in this paper are the results and analysis of a st udy of the effect of insulator shapes on the dc contamination flashove r voltage. A dynamic arc model is used for this purpose. The salient f eature of the model is that it takes into account the geometry of the insulator at every instant of the arc propagation, and thus includes t he role of geometry in the contamination flashover process. A variety of porcelain cap and pin insulator geometries that are widely used in practice have been evaluated using this model. Nonuniform pollution di stribution on insulators, which is more representative of field condit ions, has also been considered, and its effect on the flashover voltag e has been evaluated for the various geometries. Results are in good a greement with the experimental findings. Use of the model as a design tool to select type and number of insulators for HVDC transmission lin es has been illustrated.