Patent GB-786316-A (GB)
Title: Improvements in or relating to systems for energising electrostatic precipitators
IPC: G05F1/34
Filed: 1955-12-30
Abstract: 786,316. Automatically-regulated supply systems for electrostatic precipitators. RESEARCH CORPORATION. Dec. 30, 1955 [Feb. 16, 1955], No. 37439/55. Class 38 (4). A system for energizing electrostatic precipitators comprises a pair of oppositely connected thyratrons 2a, 2b, in the primary circuit of a high-voltage transformer 4 through which the precipitator sections 6a, 6b are supplied. The secondary circuit of the transformer includes a full-wave rectifier 5 whereby two direct pulsating voltages are provided for energizing the two sections. Grid phase control circuits for the thyratrons, comprise cathode resistors 208a, 208b, and across each resistor is developed an A.C. lagging bias to which is added vectorially an A.C. signal of variable phase and amplitude. Auto transformers 210a, 210b provide individual control of the thyratrons so that the precipitator sections can be adjusted separately for maximum voltage and optimum sparking rates. A small stabilizing D.C. bias is obtained by grid rectification across resistors 212a, 212b, shunted by capacitors 213a, 213b, low-value capacitors 214a, 214b prevent transient anode voltage disturbances from interfering with the grid control operation, and series resistors 216a, 216b, limit the grid current. When the grid voltage is in phase with the anode voltage, nearly the full pulse-width is utilized and appears across the respective precipitator section as a broad voltage pulse, alternate pulses being applied to one section and intermediate pulses in the opposite direction to the other section. Retardation of the thyratron firing angle produces a pulse of shorter duration but having a higher maximum value. The thyratrons, or a single thyratron, may be connected in the secondary circuit of a control transformer having its primary winding in series with the primary winding of the high-voltage transformer, Figs. 4, 5 (not shown). The series transformer may be centre-tapped so that the thyratron cathodes are at a common potential, and an input auto transformer may have tappings for matching the line voltage to the primary voltage of the high-voltage transformer, Fig. 6 (not shown). In another arrangement, the grid circuits of the thyratrons comprise an auto transformer controlled by a reversible servomotor which is, in turn, controlled by means of a magnetic amplifier, electronic integrator, and spark senser. This arrangement provides pulse-width control and automatic control for optimum sparking, Fig. 7 (not shown). In a further embodiment, the grid control of the thyratrons is effected by means of a bridge circuit having two balanced impedance arms, and a saturable magnetic transducer with windings forming the other two arms of the bridge. One of the control windings of the transducer is supplied with D.C. in accordance with the sparking rate of the precipitator, and the other control winding with a manually adjustable current. The bridge is supplied with A.C. and its output varies in magnitude and phase in accordance with the difference between the actual and desired sparking rates, Fig. 9 (not shown). Thus, the grid firing angle is advanced or retarded to raise or lower the precipitator voltage when the sparking rate is either too low or too high, whereby the system becomes self-regulating to maintain a desired sparking rate. Specifications 706,929 and 740,394 are referred to.