GB723568A - Improvement in voltage control in electrostatic precipitators - Google Patents

Abstract

723,568. Supply and switching systems for consumption apparatus. AIR PREHEATER CORPORATION. April 23, 1952 [May 3, 1951], No, 10229/52. Class 38 (4). [Also in Group XL (a)] An electricity supply system for an electrostatic precipitation of the type, described in Specification 684,024, [Group XL (a)], in which separate banks of collecting electrodes are cleaned in succession, by a rotatable pipe 38 above the electrodes, each bank being de-energized during the cleaning period, includes an individual power supply for each electrode bank, and switching and relay gear to reduce partially the voltage on each electrode bank prior to the cleaning period, and after the cleaning period to restore the voltage, first partially, and then fully. The shaft carrying the cleaning pipe 38 carries also rotary switches 67, 68 and 77 for operating the voltage supply circuits. Each power supply circuit includes a rectifier circuit 52 connected to the secondary of a transformer 51 whose primary is connected to the power lines by a circuit including ignitrons 53, 54. The ignitrons are controlled by thyratrons 55, 56 whose grids are normally biased off. An impulse transformer 57 whose primary is connected to an auxiliary power source through a phase-shifting circuit 60, applies starting impulses to the thyratron grids, over-riding the bias voltages. These impulses are supplied when the contacts 711 in the primary of the impulse transformer 57 are opened in response to the energization of a relay 71 through the cam 66 of rotary switch 68 closing contacts 70. Opening of the contacts 711 eliminates shorting of the resistor 61 in circuit 60. The impulses supplied to the thyratron grids are late in phase, and therefore delay the starting phase of the ignitrons. The voltage applied to the primary of transformer 51 is reduced, and thereby reduces the D.C. voltage applied to the precipitator bank. In the cleaning period for the bank, a rotary switch 67 energizes, through cam 69 closing contacts 72, a relay 73 which by opening contacts 731 interrupts the supply of starting impulses to the thyratron grids. The ignitrons become deenergized, and no voltage is applied to the precipitation bank. After the cleaning period first the contacts 72, and then the cam 66 is disengaged from the contacts 70. An overvoltage relay 80 is provided to operate the voltage-reducing relay 71 in the event of a flash-over in the ionizer section of the precipitator. In this event, triode 83 which controls the relay 80, loses its grid bias voltage, since with a reduction in the ionizer voltage, supplied to the ionizer section through resistor 89, glow tube 84 in series with resistor 86 in circuit 87, closes to become conductive. A further circuit associated with the grounded connection to the rectifier bridge 52, operates a relay 92 to cut off all control circuits in the event of a shortcircuit in the precipitator bank. A rotary switch 77 operates to restart the circuits automatically after the cleaning period.