Sinusoidal, Triangular, or Square Alternating Voltages Neutralization of Electrostatic Charges on the Surface of Polypropylene Nonwoven Fabric

The most widely used techniques for neutralizing the static charge at the surface of insulating bodies make use of the bipolar ions generated in an ac corona discharge. The aim of the present work is to evaluate the efficiency of the neutralization achieved with a corona electrode energized from a generator of sinusoidal, triangular and square ac voltages of various amplitudes and frequencies. The experiments were performed on 120 mm $\times$ 90 mm samples that were cut from the same nonwoven polypropylene (PP) fabric. The samples were charged for 10 s, in ambient air, using a triode-type corona electrode system of positive polarity. The neutralization was performed 300 s after the charging process, with the samples moving at constant speed (3 cm/s) in the ac corona discharge zone. The electric potential distribution at the surface of the samples was measured with an electrostatic voltmeter (model 3450, Trek Inc., Medina, NY). The efficiency of the neutralization was evaluated by calculating the inverse ratio between the maximum absolute values of the potential before and just after the neutralization. The amount and the polarity of the residual charge after neutralization depend on the frequency, amplitude, and type of ac voltage. The results show that an excellent neutralization can be obtained for any of the three wave shapes of ac voltage, at industrial frequency (i.e., 50 Hz) by varying the amplitude of the offset.