GB812277A - Automatic voltage control of precipitator rectifiers - Google Patents

Abstract

812,277. Automatic control systems for electrostatic precipitators. LODGE-COTTRELL Ltd. June 27, 1956 [June 27, 1955], No. 18528/55. Class 38 (4). [Also in Group XXXVII] An electrostatic precipitator 14 supplied from rotary rectifier 13 driven by motor 2 has cut-outs 9 and an autotransformer 4 in the primary circuit of its high-voltage transformer 12, the autotransformer being adjusted by a motor 49 having a " raise " winding energized periodically by a time relay 50, 51 and a " lower " winding energized through contacts 36 by a relay 37 itself operated by current transformer 8 and relay 39, 40 when excessive current flows in the primary circuit of transformer 12. When a heavy current of short duration flows, overload coils 10 open contacts 11 to de-energize relay 16 and so open cut-outs 9, and also open contacts 17 preventing immediate re-energizing of relay 16 and close contacts 18 energizing motor 19. Motor 19 rotates a disc 54 against spring 55 and a peg 57 on the disc operates contacts 20, 21 and 22; it first closes 20 to maintain itself energized during the cut-out reclosing cycle, then closes 21 to energize relay 23 which closes contacts 24 re-energizing coil 16 to close cut-outs 9 and holding contacts 17, and open contacts 18. Peg 57 then closes contacts 22 to short-circuit relay 23 and open contacts 24, and then opens contacts 20-22 simultaneously, switching off the motor 19. After a predetermined number of such operations (depending on the number of pegs 57) a longer peg 58 operates to close contacts 28 and energize relay 29 from transformer 52 and bridge rectifier 53; relay 29 is coupled to relay 30 and this latches closed contacts 31 in an alarm circuit and opens contacts 32 and 33. The opening of 32 de-energizes clutch 27 so that spring 55 may return disc 54 to its starting position, and the opening of 33 switches off motor 19. Thus, the overload coils act to open cut-outs 9 and then reclose them, until after a predetermined number of such operations the cut-outs are held permanently open; the apparatus is then re-started by " on " button 34 which latches relays 29, 30 in the position in which contacts 32, 33 are closed and 31 open. An " off " button 35 is also provided ; this breaks the circuit of relay 16 and also energizes relay 29 to act as described above. A time-switch 25 opens contacts 26 at predetermined intervals to de-energize clutch 27 and return disc 54 to its starting position so that " lock-off " only occurs when a predetermined number of overload trips occur in a predetermined time. " Raise " and " lower " buttons 43 and 44 allow manual adjustment of voltage, and limit switches 45 and 46 limit the travel of contact 47. An arrangement is described and illustrated in the Provisional Specification having minor differences in the circuit of relay 39, 40 and in associated circuits.