The Research Of Electrical Characteristics Of Corona Discharge Based On Isolated Metal Grounded Object

Based on laboratory experiments and numerical calculation, the corona triggering thresholds at the tip of grounded metal points and the properties of corona current have been studied analytically and numerically. In order to obtain the electric field strengths at the tip of metal tips in the case of corona discharge. Firstly, the environmental threshold electric fields must be obtained by laboratory test for different heights, shapes and materials of metal tips. Then we calculate the two-dimensional Poisson equation using finite element method and obtain the corona emission thresholds at the tip of different types of metal tips. On this basis, we investigate their effects for onset corona fields at the tip of metal tips by changing the temperatures and humidity in laboratory environment. Ultimately, the records of corona current and synchronous corona voltage were also analyzed in detail. Converting corona voltages into corona electric fields at the tip of metal tip by numerical calculation and establish the function relationship between the corona current and electric field at the tip of the metal point. We will compare corona current function in the laboratory environment with that in the field experiment. The main conclusions are as follow:(1) The environmental threshold fields are basically a linear decrease with the height of metals. The environmental threshold fields appear the trend of first decreases and then increases when metal tips are becoming increasingly sharp. The height and shape of mental tips have no effect for corona emission threshold at the tip of metal tips. The corona threshold at the tip of mental tip is a constant which is Ec=158.75kV/m. We fit a function between corona emission threshold and spatial resolution. It will provide a reference on judgment of corona discharge starting moment for the future numerical simulation of corona discharge.(2) Atmospheric conditions (temperature, humidity) have an impact on onset corona fields at the tip of ground objects. Corona emission thresholds are proportional to the relative humidities (Corona emission thresholds are basically a linear increase with the relative humidities) when the temperature remains constant. The higher temperatures, the larger corona triggering thresholds in the case of maintaining the same relative humidity.(3) Corona currents increases with the increase of the electric field strengths at the tip of metal tip are nonlinear. The relation between corona current and the electric field strength at the tip of metal object is Ic=-1.21518×10-6Ec(Ec-121.1623) when spatial resolution is lcm. For the convenience of study of the corona discharge of ground structures, the function formula between the corona current and electric field at the tip of the metal point under different resolution. Compare corona current function in the laboratory environment with that in the field experiment found that the corona threshold at the tip of ground object is bigger than that in the field experiment and the corona current is stronger than in the laboratory environment.