Study On Corona Onset Characteristics Influenced By Conductor Surface Status Under Low Air Pressure

The corona discharge on conductors should be considered when designing transmission lines, scholars at home and abroad generally think that corona onset voltage of conductor will be lower in a rainy day, but it isn't reported formally that to what extent corona onset voltage decline; As pollution adhering to conductor can form tips distorting electric field around conductor, corona onset voltage of conductor will decline, but it isn't also reported formally that to what extent corona onset voltage decline and the relation between corona onset voltage and pollution density; In our country some HV transmission lines pass through high altitude region some of that is over 3000meters. As is well-known that air pressure will be decrease with altitude increasing, as air pressure decreases, corona discharge characteristics of conductor under contamination or rain conditions are unknown, so the study on corona onset characteristics influenced by superficial conditions of conductor under low air pressure has theoretical and practical values. The effects of atmospheric parameters on corona discharge were carried through for demands of practical engineering, some empirical formulas to modify corona onset voltage are proposed, as relative air pressure and humidity in the experiments are limited, and the methods to estimate corona onset voltage are different from each other, so the results can't be applied extensively. On the basis of existing production, this paper performs a mass of experiments in the corona cage, the effects of water drops and pollution as well as relative air density and humidity are analyzed. The main conclusions are as follows:①The method to estimate corona onset voltage based on the relation between discharge quantity and applied voltage is quite accurate. The law of photons varying with voltage is coherent to the relation between discharge quantity and voltage when conductor is slick. On the relation curves between discharge quantity and voltage is there an obvious turning point which don't exist on the relation curve between photons and voltage when conductor is in rainy and pollution.②The effects of quantity of water drops on corona onset characteristics of conductor are studied in this article. The rusults indicate that corona discharge will experience three stages while one or two water drops are adhering to conductor: discharge caused by unstability of water drops, discharge by ionization of gas and absolute corona discharge of conductor in turn; there is no obvious boundary between the first and second stage while much water drops adhere to the conductor.③Corona onset characteristics of conductor adhered with much water drops under low air pressure are also studied. It shows that corona onset voltage will obviously decrease; the corresponding surface roughness coefficient m is between 0.62 and 0.65.④By transforming ESDD and NSDD, the effects of pollution density on corona onset characteristics are investigated. It indicates that there is no obvious relation between corona onset characteristics and ESDD and NSDD.⑤Corona onset characteristics of conductor adhered with pollution under low air pressure are studied. It shows that corona discharge of contaminated conductor under low air pressure is more serious than normal pressure; the corresponding surface roughness coefficient m is between 0.67 and 0.79.⑥The effects of relative air density and relative humidity on corona onset characteristics are performed. The results show that corona onset voltage decreases with decreasing of relative air density; as increasing of relative humidity, corona onset voltage shows a trend that increases firstly then declines; as diminishing of relative air humidity, the characteristic exponent of effects of relative air density on corona onset voltage increases; as increasing of relative air humidity, corona discharge quantity of corona onset also shows a trend that increases firstly then declines.⑦Emendation formula of corona onset voltage of conductor:(only for coaxial column conductor)...