The accumulation of surface charge due to a conducting particle on a spacer

The electrical properties of the widely used gas inslulated systems for switchgear depend strongly on the properties of the used gas. Electrical fieldstrength and the field distribution determine the behaviour. If the field gets disturbed the insulation properties decrease significantly. Conducting particles lead to local field enhancement. Especially when these particles get stuck on a spacer surface, the fieldstrength in the vicinity of the particle is increased. This increase in fieldstrength yields more ionization and can result in a dielectric failure. To investigeate the behaviour of particles on spacers a simplified spacer model with an adhering particle was tested under homogenous field conditions in SF 6 . The gas pressure and the particle length were used as parameters. Investigations on the electrical strength and charge distribution were performed under clean and particle contaminated conditions The surface charge accumulated during AC and LI stress and its distributio was measured during the experiment. A specially designed setup was used to aquire the surface charge data; stressing the sample and subsequent measurements of the charge distribution could be performed without distortion of the latter. This enabled the application of voltage stress to a known charge distribution. Thus the effects of surface conditioning and decreasing or increasing insulation strength could be studied. Special attention was paid to the charge distributions concerning on-site test procedures.