Abstract: In a system for controlling electric power supplied to corona-generating electrodes in an electrostatic precipitator (10), an opacity-sensitive transducer (20) produces an output signal proportional to the opacity of the flue gas exiting from the precipitator (10). The signal from the transducer (20) is compared in comparators (304 and 305) with pre-set upper and lower limits defining a permissible opacity range for the flue gas. When the signal from the transducer (20) exceeds the pre-set upper limit or falls below the pre-set lower limit, automatic voltage controllers (40) are activated to control the power supplied to the corona-generating electrodes in order to restore the flue gas opacity to the permissible opacity range.

Abstract: An improved precipitator voltage control system including an automatic voltage control (AVC) circuit, a firing circuit, an alarm circuit, a power-saving circuit, a remote set-point control circuit and a power supply, all of which are mounted on a single, readily interchangeable circuit board. The automatic voltage control circuit includes a highly responsive spark detection subcircuit which causes the transformer/rectifier voltage to be reduced to zero at the end of the half-cycle in which a spark occurs and then causes the voltage to remain at zero for a short period of time after which voltage is reapplied in a dual ramp manner causing it to rapidly reach a level below the precipitator arcing potential and then increase at a slower rate to the threshold of sparking. The firing circuit drives silicon-controlled rectifiers (SCRs) through optical couplers which provide several thousand volts of circuit isolation.