Sparks in a small gap between HV spherical metal electrode and corona-charged organic film

Sparks between a spherical metal electrode and corona-charged organic film were studied in air at room temperature. dc and impulse high voltages (HV) were applied to the spherical metal electrode, the polarity of which was opposite to that of the charge on the film. The maximum surface voltage of the corona-charged film was ±2 kV. The gap length was studied in the range 0.2 to 2.5 mm. Films of PTFE, PP, PS and PET of thickness 30 to 50 μm, were tested. In the case of negatively charged films, the electric field strength depended on the film material; the spark field strength decreased in the following order: PTFE⩾PP>PS⩾PET. The dependence of spark field strength on the material of negatively charged film was observed under both dc and impulse voltage applications. In the case of the positively charged films, the spark field strength showed less dependence on the film material. The experimental results are explained in terms of the degree of electron emission from negatively charged PTFE being higher than that from negatively charged PET