Abstract: A method of controlling the pulse frequency of an electrostatic precipitator energized by a pulse superimposed direct voltage, is disclosed in which, for a given direct and/or pulse voltage, the pulse repetition frequency, at intervals which are preset or determined by one or more precipitator or operational parameters, is lowered and then increased stepwise according to a predetermined scale. At each value of the pulse repetition frequency the average current being measured and the transmitted charge per pulse (defined as the average current divided by the pulse repetition frequency) calculated.

Abstract: In the method of controlling the period length of an intermittent voltage supply to an electrostatic precipitator, a search procedure is carried out at predetermined time intervals or at time intervals determined by one or more continuously monitored/measured precipitator or operational parameters. During the search procedure either the number of system voltage half-periods during which the power supply to the precipitator is cut off (the length of the non-conduction (n.sub.p) period), or the number of system voltage half-periods during which the power supply supplies current to the precipitator (the length of the conduction period), are changed according to a predetermined scale or to a scale determined by one or more precipitator or operational parameters. The charge transmitted per system half-period is current in the precipitator divided by the total number of half-periods of conduction per second.