Factors That Influence the Decay Rate of the Potential at the Surface of Nonwoven Fabrics After Negative Corona Discharge Deposition

Surface potential decay (SPD) measurements are considered as the most appropriate technique for the investigation of the corona charging of dielectric surfaces. The aim of the experiments reported in the present paper was to point out the peculiarities of SPD in the case of nonhomogeneous dielectrics, such as the nonwoven fabrics employed for heat, ventilation, and air conditioning. This paper reports experimental data collected on two types of polypropylene (PP) media, characterized by different fiber diameters. The experiments were performed on 60 mm × 50 mm samples of nonweaved sheets of PP (sheet thickness: 400 μm; average fiber diameter: 20 μm), in ambient air (temperature: 18°C to 22°C; relative humidity: 25% to 60%). The samples were charged for 10 s by exposing them to the negative corona discharge, using a triode-type electrode arrangement, energized from a dc high-voltage supply. Their surface potential was then measured with an electrostatic voltmeter. The measured data indicate that the charge of the filter is limited by the local discharges that occur inside the fibrous dielectric.