GB1154972A - Electrical Control Method and Apparatus - Google Patents

Abstract

1,154,972. Control systems for electrostatic precipitators. JOY M.F.G. CO. 23 Aug., 1966 [30 Sept., 1965], No. 37685/66. Heading H2H. A control system for an electrostatic precipitator comprises means whereby the average discharge electrode voltage is maintained at a maximum value. The precipitator 10, 12 is supplied from an A.C. source 13 by way of a step-up transformer 14 and rectifier 18, the voltage across the precipitator electrodes being controlled by way of a saturable reactor 22 serially connected between the A.C. source and the primary winding of the transformer 14. A signal proportional to the voltage across the precipitator electrodes is fed to a transformer 32, 33 and is then rectified to give a steady D.C. signal by a rectifier and filter 34. The output of the rectifier 34 is fed to a dual time constant unit 36 having a short time constant whilst the precipitator voltage is rising and a long time constant whilst the voltage is falling and the output voltage of this unit 36 is fed to a polarized differentiating unit 38. The unit 38 is constructed to produce a D.C. output signal only when the precipitator voltage is falling and this signal is proportional to the rate of decrease of the precipitator voltage. The output voltage of the unit 38, after amplification, controls a trigger circuit 42 which produces a single output pulse each time it is energized from the unit 38. The pulses are amplified and used to control a "flip-flop" unit 48 whereby alternate output signals of opposite magnitudes are produced. These signals control a scan generator 52 whereby alternately rising and falling D.C. outputs are derived having a slow rate of rise or fall. The output of the generator 52, suitably limited and amplified, is used to feed the control winding 24 of the saturable reactor 22 and thus to control the voltage applied to the precipitator electrodes 10, 12. Thus, should the precipitator voltage tend to fall along a curve 66 on either side of a maximum value 68, the reactor 22 will receive a signal to return the voltage to the value 68. A time delay unit 50 may be provided to prevent false operation of the control circuit and a filter unit 73 provided to isolate the units before the filter from those after the filter. Furthermore a switch may be incorporated in the control circuit so as to enable manual control of the precipitator voltage to be made. The saturable reactor may be replaced by a thyristor.