Study On Pollution Flashover Performance Of Typical Insulators Intended For EHV/UHV DC Transmission Line

The flashover of polluted insulators is the one of the key issues to threaten the safe operation of transmission line. Compared with the AC insulators, the contamination deposited on DC insulators is more and the external insulation design of DC transmission lines is more difficult. A mass of investigation of DC pollution flashover has been studied in China and the world, but there is less investigation about pollution flashover of the larger insulators intended for EHV/UHV DC transmission lines.Based on the needs of external insulation design of Yun-Guang±800kV UHV DC transmission project, six types of typical porcelain and glass insulators intended for EHV/UHV DC transmission lines are tested in an artificial climate chamber. Based on the tested results and analysis, the thesis studies the DC pollution flashover performance of the insulators and the developed rule of the partial in the discharge process.Based on the experimental and analysis, the conclusions in the thesis are as follows:①In the artificial pollution tests, the flashover voltage Uf of porcelain and glass insulators decreases with the increasing of salt deposit density SDD. The exponent a charactering the influence of SDD on Uf is relative with the configuration and materials of insulators, whose value is between 0.32 and 0.55. a of fog insulators are smaller than those of outer-rib insulators.②At the lighter pollution degree, the flashover voltages of two-outer-rib type and three-outer-rib type insulators are higher than fog type insulators and the former's flashover voltage gradients along creepage distance are higher. But, at the heavier pollution degree, the flashover voltages of the fog type insulators are higher than the two-outer-rib type and three-outer-rib type insulators. The fog type insulators have better anti-pollution performance in the heavy pollution areas.③Under the same condition, the flashover voltage gradients along creepage distance and along arc distance and valid coefficient of creepage distance of the glass insulators are higher those of porcelain insulators.④There are three stages in the development of DC discharge of polluted insulators: the formation of partial arc,pause partial arc and development stage of partial arc to flashover. The development velocity of partial arc of various types of insulators is related with the materials and configurations of insulators. The velocities of porcelain insulators are faster than those of glass insulators, the velocities of outer-rib type insulators are faster than those of fog type insulators.⑤Based on comparison of the electrostatic force, electromagnetic force and thermal buoyancy, the reason of forming arc-floating is analyzed. The electrostatic force is the main one and partial arc develops mainly along the surface of insulators when the leakage current is smaller, while the thermal buoyancy is the main one and partial arc divorces from the surface of insulators when the leakage current is larger.