Experimental Study of Charge Neutralization at the Surface of Granular Layers of Insulating Materials

Neutralization of the residual electric charge is often a prerequisite for the optimal processing of insulating granules, thin films, or textile media. The aim of this paper is to evaluate the factors that might affect the ability of ac corona discharge to eliminate the charge at the surface of polyethylene granular materials. The effectiveness of the neutralization is evaluated from the measurement of surface potential distribution before and after exposing the samples to a flux of bipolar ions. The corona discharge was generated by energizing at various high-voltage (HV) levels (16, 20, and 25 kV) and frequencies (1, 20, 50, 100, 200, and 400 Hz) a wire-type corona electrode suspended at 30 mm above the granular layer disposed at the surface of a grounded plate. The results show that the neutralization efficiency can be improved by increasing the frequency of the HV. An optimal value voltage can be experimentally determined for the case of practical interest when the frequency of the power supply is 50 Hz. In the same case, successive exposures to the ac corona discharge may enhance the efficiency of the neutralization.