Phase Defect Angle of an Air Capacitor

Abstract

This investigation was undertaken in order to determine the conditions of atmosphere under which the air capacitor may be regarded as having zero loss. A special guarded and shielded test capacitor was constructed having quartz insulation between the high-voltage and guard plates and low loss molded bakelite insulators between the measuring and guard plates. This capacitor was enclosed in a metal box and subjected to various conditions of temperature and humidity. Readings were made of continuous conduction current and a-c. phase defect angle. The measuring instruments used were the most sensitive available. A D' Arsonval galvanometer having a sensitivity of 1.5 × 10^-12 amperes was used in the continuous current work and a Wien bridge sensitive to three seconds in the a-c. measurements. A gradient of approximately 4000 volts per cm. was used in all tests. Measurements were made of the effect of humidity at temperatures from 60 deg. fahr. to 100 deg. fahr. and in each run the humidity was varied from 40 to 95 per cent, approximately. Readings were made of continuous conduction current and the phase angle of the test capacitor was compared with that of a standard air capacitor in which the humidity was maintained at a low value. It was found that the conduction was zero and the phase defect angle of an air capacitor was less than three seconds for values of humidity below 90 per cent.