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Vacuum Capacitors

Introduction


A vacuum variable capacitor uses a high vacuum as the dielectric instead of air or other insulating material. This allows for a higher voltage rating and/or capacitance value using a smaller total volume. In addition to the higher voltage rating a vacuum dielectric greatly reduces the chance of arcing between the plates. There are several different designs in vacuum variables, the most common geometry of the capacitor plates is usually inter-meshed concentric cylinders. The meshed cylinders are contained within a ceramic vacuum envelope, similar to an electron tube. Metal bellows are used to maintain vacuum seal while allowing positional control for the moving parts of the capacitor.

What is vacuum?

Vacuum is the state of gas with an smaller molecular density than that of air. (Air pressure: 2.7×1019> high vacuum: 2.7× 1010 piece/cm3). Since the gas molecule density is extremely low in a high vacuum, the charged particles (gas molecules) coming out of the cathode hardly collide with the residual gas molecules. The vacuum controls the breeding of charged particles after collision without reducing the dielectric breakdown voltage. Therefore, the vacuum has the insulating performance ten times greater than that of air.