EFFECT OF VOLTAGE WAVE-FORM ON PARTIAL DISCHARGE IN FERROELECTRIC PELLET LAYER FOR GAS CLEANING

Characteristics of the partial discharge in a ferroelectric pellet layer have been studied using ac voltages with varying frequency or using square wave voltages. The capacitance of the layer, Ct, consists of the capacitance of each ferroelectric pellet, Cp, and the capacitance of the air gap between each pellet, Cg. Since Cg is much smaller than Cp, the capacitance of the layer is determined mainly by Cg. Therefore the packing of ferroelectric pellets with a large dielectric constant does not increase the value of Ct significantly, and an excessive increase in the capacitive charging current can be avoided. With an ac voltage application, the partial discharge takes place when the voltage crosses zero, and ceases when the voltage reaches positive or negative peak value. The partial discharge consists of many pulsive discharges with less than 1 mu s duration. With the increase in frequency of the ac voltage, the period of the partial discharge is widened, and the maximum value of the current pulse, Ip max is increased. At higher frequency, the partial discharge can be generated in a pellet layer with smaller dielectric constant values. The larger the value of the dielectric constant of the pellet, the larger the Ip max of the pulsive discharges becomes. When a square wave voltage is applied, a very large current can be obtained during the transient period of the voltage. The value of Ip max should affect the plasma temperature of each pulsive discharge, and should affect the efficiency of the plasma chemical reaction for each discharge. Reaction speed should be proportional to the number of the pulsive discharges for 1 s. The gas cleaning performance of the partial discharge can be adjusted by varying the dielectric constant value, the voltage waveform, and the frequency.