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Reference: ISH2015_287

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Study on the Characteristics of Surface Charging in a Vacuum Insulation System



Flashover along surface of a solid insulator is one of the important problems for vacuum insulation systems. In order to mitigate the electric field at the junction between an electrode and a solid insulator, which is a primary cause of surface discharge, shield rings are applied to the electrodes. This paper presents a study on the charge distribution on an insulator surface in a vacuum insulation system. The main objective of this work is to clarify the charging characteristics and the effects of the shield rings on the charge distribution. The configuration of study consisted of a hollow cylindrical alumina insulator set between parallel electrodes. The tip radius and the position of the shield rings were varied for investigating their effects. After an application of 25 kV potential to the electrodes, we measured the charge by using a guarded electrostatic probe to collect the induced-charge data at different vertical and azimuthal positions. From the measured data, we determined the charge distribution on the inner surface of the cylindrical insulator by using an inverse calculation. The method of ? function was applied to construct the relationship between the surface charge on the insulator and the induced charge on the probe. The finite element method was used to calculate values of the ? function in 3D conditions. For solving the charge distribution, we assumed a condition of axisymmetric charging. The Tikhonov regularization was applied to smooth the charge fluctuation. Our results clearly show that the use of a shield ring can significantly lower the degree of surface charging. We have also found that the geometries of the shield ring have a remarkable effect on the surface charging. High electric field at the ring tip may charge the insulator surface near the tip. The ring tip in close proximity to the surface may also increase the magnitude of the surface charge.

File Size: 815 KB

Year: 2015

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