Discharges that occur when a grounded object approaches an electrified insulating surface

When a grounded metal sphere approaches a charged polyethylene terephthalate sheet (75-850 mu m thick) backed by a grounded metal layer, discharges occur. The discharges are called approaching discharges. In an experiment, with a 130 mm diameter backing electrode, two modes of discharge were studied: small (Polbuschel) and large (Gleitbuschel). When an approaching Gleitbuschel initiates, it spreads over the entire charged surface simultaneously. The approaching Gleitbuschel is apparently very hazardous. To avoid it, one must not electrify a thin and wide insulating layer on a grounded object negatively.<>