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Reference: ISH2015_110

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Breakdown Charge Dependence for Saturation of Spark Conditioning under Non-uniform Electric Field in Vacuum



Spark conditioning is one of the effective measures to improve the dielectric strength in vacuum. In this paper, we discuss breakdown charge dependence and a saturation condition of spark conditioning in vacuum under various non-uniform electric field and circuit condition. We used a rod-plane electrode system, and the gap distance and the tip radius of the rod electrode were varied. Negative lightning impulse voltage was applied to the rod electrode for the spark conditioning of electrodes. We changed the discharge current at breakdown by the circuit condition, i.e. the limiting resistance. As a result, as the breakdown charge increased, the dielectric strength was improved. However, when the breakdown charge was too large, the dielectric strength decreased due to the damaging effect of the electrode. Consequently, the conditioning effect has the maximum value, and the amount of breakdown charge to achieve the maximum conditioning effect depends on the physical properties of electrode materials, e.g. melting point and specific heat capacity. In addition, the dielectric strength at the cathode surface after completing conditioning depended on the amount of breakdown charge, regardless of the gap distance and the tip radius. Because a high electric field is formed at a low voltage under non-uniform electric field, BD based on the cathode heat theory mainly occurs. Therefore, the saturation condition of spark conditioning under non-uniform electric field is decided by the electric field at the cathode surface and the amount of breakdown charge. From these results, we can estimate the achievable withstand voltage by spark conditioning from the electrode material, the electrode configuration, and the circuit condition.

File Size: 571,5 KB

Year: 2015

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