Influence of the Gas Volume Size on Spacer Charging in Sf6 under Dc Stress

As Gas Insulated DC transmission systems unite the advantages of space saving installation and large transmission capacity this technology is increasingly discussed and investigated today. The main problem in operation with respect to insulation seems to be identified today, which is charge accumulation on the surface of the spacer. These trapped charges can cause a reduction of dielectric strength and can lead to breakdown, especially at polarity reversals and overvoltages. The experiments presented in this paper deal with the influence of the volume of the gas phase on the charge accumulation. Ion from the gas phase drift in the DC field along the flux lines. If these lines end on the insulator surface, charges accumulate and distort the background electric field distribution. The amount of charges accumulated on the insulator surface increase with field strength only for very small applied voltages as a saturated drift is quickly reached. The main influencing parameter is thus the volume of the gas phase that is connected to the surface via the flux lines. To investigate and quantify this effect in detail the volume of the active gas phase, i.e. which is connected to the surface by flux lines, was varied for the presented experiments and the surface charge accumulation on the spacer was measured.