Influence of freon on charge density build-up in a solid insulator

The charge generation at the surface of and within an acrylic glass spacer was measured using a capacitive probe in freon as a function of gas pressure and the level, duration and polarity of a dc applied voltage. Typically the rate of charge build up increased with increasing gas pressure from 0.174 μC/m²/s at 0.1 MPa to 0.97 μC/m²/s at 0.4 MPa a fixed applied voltage of 80 kV. At a fixed gas pressure of 0.1 MPa the charge build up increased from 2.6×10^-3 μC/m²/s at 2 kV to 174×10 ^-3 μC/m²/s at 80 kV. The saturated charge density increased linearly with increasing voltage from 1.3 μC/m² at 2 kV to 61.2 μC/m² at 80 kV, for 0.1 MPa. The charging current was also monitored and found to decrease rapidly with increasing time until saturation is reached. The saturated current increased, at a fixed pressure, with increasing voltage. It also increased with increasing pressure at a fixed applied voltage. The observed charge build up is governed by the total surface and volume resistances of the insulator