Precipitator voltage control system

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. The alarm circuit detects short-circuit and open-circuit conditions and causes automatic trip-out of the control circuit when such alarm conditions exist. The power-saving circuit allows operation of the precipitator to be monitored and the voltage thereof to be reduced during high resistivity conditions. The remote set-point control allows the drive current to be controlled from a remote source.