Experimental modeling of the electric potential decay at the surface of polypropylene films (PP)

Abstract Surface potential decay (SPD) measurements have been considered as the most appropriate technique for the investigation of the corona charging of dielectrics. The aim of the present paper is to point out the interactions between three factors namely: grid potential, grid current and sample size (length), by taking advantage of the experimental design methodology. The experiments were performed on 0.08 mm – thick samples of PP films, in ambient air (temperature: 20 °C–22 °C; relative humidity: 56 %–62 %), The domains of variation of the three factors considered in the experiments were as follows: – 8 to – 12 kV, for grid potential – 50 to – 90 μA for grid current and 70–150 mm, for sample length. The relative SPD after 300 s and 900 s were considered as output variables of the process. The models that express these variables as quadratic polynomial functions of the three factors were obtained using the Design of Experiments methodology and the commercial software MODDE 5.0. They point out that the surface potential decay is faster at higher applied voltages, lower grid currents and smaller sample areas. The grid voltage has a stronger effect at lower values of the grid current. Both the grid voltage and the corona current have a stronger effect of the SPD in the case of the samples of smaller areas. These observations suggest the optimal operating conditions of the corona charging devices for this kind of dielectric materials.