Precise capacitance measurements of high-voltage compressed gas capacitors

The parameters affecting the capacitance measurement of compressed gas capacitors which are used as high-voltage standards are investigated. The temperature coefficient of compressed gas capacitors in the range of 2 to 3 · 10⁻⁵ K⁻¹, as well as inevitable ambient temperature changes and gradients within high-voltage halls, were found to be mainly responsible for the limitation in the accuracy of precise capacitance measurements. A method is given to distinguish between capacitors with high- and low- voltage dependence of capacitance, without applying high voltage to them. The voltage dependence of a commercially available 120-kV, 100-pF capacitor could be considerably reduced by renewing and readjusting its electrode system. The natural frequencies of the mechanical electrode system of capacitors with rated voltages between 100 and 800 kV were found to be between 38 and 8 Hz, respectively.