GB859784A - Improvements in or relating to automatic control systems, for electrostatic precipitators - Google Patents

Abstract

859,784. Automatic control systems for electrostatic precipitators. LODGE-COTTRELL Ltd. Feb. 24, 1959 [Dec. 30, 1957], No. 40330/57. Class 38 (4). In an electrostatic precipitator the average discharge electrode voltage, defined as the average voltage applied to the electrodes over a fairly long time interval, of up to several seconds, is maintained at a maximum value by means responsive to the rate of change of the electrode voltage. A variable ratio transformer VR, Fig. 2, supplies a high-tension transformer TR the output of which is applied via a rotary rectifier to a precipitator P. A voltage proportional to the electrode voltage is derived from a tapping B of a potential divider and after amplification by a high-gain pentode PV, Fig. 3, applied through a capacitor C4 to a power winding of a magnetic amplifier. A process-timer PT sequentially closes a " raise " contact PR, causing a regulator motor RM to move the slider of the transformer VR, and then after a short period opens the ' raise " contact and closes a " lower contact PL applying a voltage to the regulating motor dependent on the reactance of a transductor SR. The rectified control output of the magnetic amplifier is applied to a winding DC1 to vary the reactance of the transductor in dependence on the rate of change of the electrode voltage during the " raise period so as to tend to maintain the average electrode voltage at a maximum value. When the magnetic amplifier is arranged to respond to an increase in average electrode voltage, a winding DC2 is energized to set up a magnetizing flux opposing that of the winding DC1. In a modification, the valve amplifier is not used and the magnetic amplifier has two power windings with differing time constants directly connected to tapping B. In a further modification, the magnetic amplifier is arranged so that the output control current depends on the direction of change of the precipitator voltage. The output from a current transformer CT through a thermal relay S2 actuates a relay EM to drive the regulator motor in the "lower" direction when the primary current of the H.T. transformer exceeds a predetermined value. Specification 832,342 is referred to.