Generation of surface charges on an insulator in SF6 gas

The build up with time of the accumulated charge density on an acrylic glass rod insulator having a fixed length and fixed diameter of 30 mm was measured in SF₆. The charge density is found to increase linearly with increasing voltage at a fixed pressure, to increase linearly with increasing gas pressure in the range 0.1-0.13 MPa, to be almost constant in the range 0.13-0.5 MPa at a fixed applied voltage, and to increase with increasing voltage at a fixed E/p. The rate of charge build-up depends on time; it initially increases rapidly, and then increase slowly until saturation is reached. The charge polarity corresponds to that of the adjacent electrode. These results suggest that the role of the ionized species within the volume of the gas in charging the insulator is less significant than the charging of the insulator by injection of current from the electrodes, which is governed by the total surface and volume resistances of the insulator