Construction and Behavior of a High Voltage Cylindrical Condenser

Abstract

Cylinders of lumite glass 35 inches long by 10¼-inch diameter (such as are used on gasoline filling-station pumps) were used for dielectrics, and 0.005-inch aluminum foil for plates. A 7-inch glass margin was left at the ends of the cylinders. Each condenser had a capacity of 0.012 microfarad and would withstand steady voltages of over 100 kilovolts without ``flashing over.'' Sets of rings of 516−inch copper tubing were made to fit the cylinders at the edges of the plates, both inside and out. The rings provided a ``curled'' or ``rounded'' edge, in place of the rather sharp edge of the foil itself. The effect upon the ``edge corona'' and ``flash-over voltage,'' due to various-width bands of aluminum paint on the glass surface adjacent to the metal-plate edges, was tried, with and without the above-mentioned rings, in disruptive discharge and steady-voltage tests. The results showed that the highest voltages could be obtained, without break-over occurring, when the glass margins were chemically clean. It was also found that the best type of plate-edge construction was either the plain aluminum-foil edges without paint, or the curled edges (i.e., with copper rings) with a ¼-inch band of paint.