Calculation And Study Of The Space Electric Field In Long Rod-Plane Gap Discharge

For the cross of multi-disciplinary and the lack of advanced apparatus to measure the parameters of air discharge, the research on high-voltage and insulation technology was mainly based on experiments. The simulation experiment and real experiment both have many deficiency and will take many human power and financial resources, especially for the external insulation research of the ultra-high voltage (UHV) and extra-high voltage (EHV) which will involve the discharge of long air gap and long insulator string under the complex environment, if the research was developed on the real voltage and real dimension it would cost much but found the rule of discharge. For the reasons above we take the method of emulation to research the external insulation of UHV (EHV) and this will accelerate the discipline of high-voltage and insulation from semi-physical research into physical research.In this article, the air gap discharge model was established in finite element method (FEM), the whole process of air discharge was calculated and analyzing, the results obtained as follows:①The space charge density of electrons and irons had to reach 108cm-3 to start the stream discharge and reached 1012cm-3 when the leader discharge starting, at this time the efforts of space charge and applied voltage to the space electric field were correspondence.②The space electric field influences the ionizing rateаand further influences the space charge density, at the same time the variation of space charge density could change the space electric field distribution in air gap. But the attachment rateη,the association rateβand dissociation constantγhave small influences on electric field distribution.③In the plasma-corona cloud model, the efforts of different length corona cloud to space electric field are regular just when the electric field in head of the corona reached 11kV.cm-1 and 3kV.cm-1 inner, the corona can develop forward. The humidity of air influences the breakdown voltage deeply and the lower humidness the lower breakdown voltage.④In the leader development model, when applied 500kV,250/2500μs switching over-voltage, the ion density in the leader channel can reach 1013～1015cm-3 and the electric field reach 1～2kV.cm-1, the time to start leader discharge is about 400μs and the velocity of the leader development is about 3×104m.s-1 from rod electrode to plane electrode. The leader channel takes 3/5 of the whole gap, it's very approach to the tested value 2/3.Both of the plasma-corona model and the leader growth model in this article can describe the long air gap discharge process perfectly. By the emulation and calculation of the process of leader discharge, we gained the starting condition of the leader and the breakdown condition of the long air gap.