The threat of pollution flashing to the safe operation of the power grid is becoming more and more serious. The failure and harm of the transmission line due to pollution flash is second only to the lightning accident. The correct selection and use of the transmission line insulators can ensure the safe and stable operation of the insulators, thereby reducing power outages and line operation and maintenance. To this end, through the analysis of the mechanism of pollution flashover discharge of the transmission line insulators, according to the factors affecting the pollution of the line insulators, measures to prevent the occurrence of pollution flashovers on the lines are proposed, and the pollution flashover accidents of the operating lines are reduced.
I. Pollution flashover and mechanism
In the long-term operation of insulators, dust particles in the atmosphere are deposited on the surface to form a pollution layer. In dry climate, the resistance of the pollution layer is large, and the insulation performance is not reduced, but under meteorological conditions such as fog, dew, light rain and snow, After the electrolyte in the contamination layer is wetted, the surface conductivity is increased, the insulation performance is decreased, and the ash therein retains moisture, which promotes further moisture absorption of the contamination layer, thereby dissolving more electrolyte, causing flashover discharge of the wetted surface of the insulator. flash. A significant feature of insulator flash discharges is the low flashover voltage, which can be as low as 10kV and below. The standard insulator has an average flashover voltage of 75kV per piece in the dry and clean state and 45kV in the wet state. The creeping discharge process of the dirty insulator is completely different from the cleaning surface, and is no longer a simple air gap breakdown phenomenon. It is a thermodynamic equilibrium process of ionized surface gas ionization, surface layer heating and drying, and local arc generation and development related to electrical, thermal and chemical factors. Macroscopically, the process of pollution flash discharge can be divided into four stages, namely, the fouling of the surface of the insulator, the wetting of the fouling layer, the formation of dry zones, the generation and development of partial discharges and the flashover of the surface. Therefore, the three elements of the flashover are the surface area of the insulator, the wetness of the contamination layer, and the voltage.
II .The cause analysis:
(1) Dust pollution
As the wind blows or transports vehicles, agricultural machinery, etc., the dust in the air flies and gradually falls onto the surface of the insulator to form a foul. Dust does not contain a large amount of conductive substances, so the threat to the line is not significant. For example, the use of a large amount of chemical fertilizer in the farmland and the increase of the conductive substances in the dust can easily cause the insulator string to fail.
(2) Saline-alkali contamination
In the line in the saline-alkali area, the dust containing salt particles is blown by the wind and accumulated on the insulator to form a salinity contamination. Saline-alkali pollution is a serious hazard to the line, especially in the saline-alkali areas of sand or semi-sand, often due to dust storms, resulting in serious salinity and pollution.
(3) Seawater pollution
The line is close to the coast, and the waves hit the coast to cause sea water splashing or seawater particles. They are blown by the wind and blow them away from the coast. Once they fall on the insulator, in the dry weather conditions, the water evaporates, and the tiny particles of sea salt It is deposited on the insulator to form seawater contamination.
(4) Industrial pollution
Such as coal-fired power plants, chemical fertilizer plants, cement plants, coking plants, glass plants, metallurgical plants and other industrial and mining enterprises, so that the smoke and exhaust gases are dispersed in the air, when they fall on the insulator string, it will form industrial pollution. These contaminated materials may be liquids, gases or solids.
(5) Bird droppings
In the multi-bird area, it occurs mostly in the area where the seasonal birds are clustered. The bird group stays on the cross arm, and the bird droppings fall on the insulator string to form bird droppings.