Ayumu Morita

Surface charges on alumina in vacuum with varying surface roughness and electric field distribution

We investigated the charging characteristics of alumina in vacuum with varying surface roughness, and the electric field distribution. The charging on the alumina surface in vacuum is, in general, strongly influenced by field electron emission (FEE) and secondary electron emission avalanche (SEEA). We varied the surface roughness and the electric field distribution on the alumina surface in order to control the FEE and the SEEA. Under these conditions, we measured the 2-dimensional distribution of surface charging potential on the alumina surface. From the measurement results, we quantitatively discussed charge polarity and charge density on the surface for various types of electric field distributions. Finally, we successfully propose a concept of a charging control technique on the alumina insulator in vacuum for the improvement of electrical insulation performance on the alumina surface.

Composite insulation structure for medium voltage class switchgear

A Next generation medium voltage Cubicle type Vacuum Insulated Switchgear (C-VIS) has been to deliver high reliability for electric power systems. A composite insulation without SF6 gas is applied to the C-VIS, and realizes environmentally friendly system with compact equipment size. The movable electrode in the double-break three-position vacuum switch is connected to the vacuum and air insulating rods in series. The air insulating rod prevents an earth fault even if a vacuum leakage occurs. The combination of the air insulating rod and the vacuum leakage monitoring system contributes to improving reliability. The air insulating rod is electrically connected to the vacuum chamber of the double-break three-position vacuum switch. Hence, the air insulating rod was designed by clarifying the induced voltage of the vacuum chamber in actual operations, and the insulation performance was verified with enough margins.

Influence of surface charges on alumina dielectrics on impulse flashover characteristics in vacuum

In this paper, we investigated the surface flashover characteristics under the existence of surface charge on alumina ceramic insulator in vacuum. We investigated the surface flashover voltage with varying the location and magnitude of surface charge. We discussed the surface flashover mechanisms under the existence fo the surface charges of alumina dielectrics in vacuum.