GB905575A - Improvements in or relating to electric circuits for the automatic control of electric drives of steam-boiler blowers - Google Patents

Abstract

905,575. Control of several motors. PRVNI BRNENSKA STROJIRNA, ZAVODY KLEMENTA GOTTWALDA, NARODNI PODNIK. Jan. 6, 1960, No. 497/60. Class 38 (3). A circuit for the automatic control of electric drives of steam-boiler blowers, arranged so that only one blower is operative at a time and a subsequent blower is set into operation as soon as the preceding blower has ceased to operate, comprises a step selector 1 having two systems of contacts 12, 13, each contact of system 12 being connected in the circuit of an operating coil 3 of a respective main contactor having normally open contacts 16 controlling the main leads to one blower 39 and two normally open auxiliary contacts 14, 15 each connected in the circuit of a separate one of the operating coils of a reversing contactor 2 common to all the blowers. Closure of switch contacts 28 energizes the coil 3 through a circuit including contactor 6 with contacts 18, 19, the contacts 13, contactors 4 and 5 with contacts 21 and 17, and as shown, the contact b in the system 12; the main contacts 16 thus close and connect the motor 39 of the blower to bus-bars 38. The auxiliary contacts 14 close and prepare a future connection between bus-bar 34 and auxiliary bus-bar 36 via contacts 26 of a limit switch, and auxiliary contacts 15 close to connect bus-bar 34 to auxiliary bus-bar 37 via contacts 27 of another limit switch. Operating coil 10 of the reversing contactor 2 is now energized, and the main contacts 31 close and link the bus-bars 38 to the mains intake lead 40 whereby mains voltage is applied to motor 39 and the blower begins to move to its operating position. As soon as the blower leaves its initial position the limit switch contacts 26 are closed; when the blower reaches its extreme operating position the limit switch contacts 27 open, whereby coil 10 is de-energized, contacts 23 are closed, coil 11 is energized, contacts 32 close and motor 39 begins to move the blower back to its initial position where it is brought to a standstill as the switch contacts 26 open to de-energize coil 11. The de-energized contactor disconnects normally open contacts 25 whereby the circuit of a coil 8 is interrupted and its contacts 22 momentarily cause coil 9 to be energized causing the arms of selector 1 to move one step forward, thus connecting the next set of contacts and automatically setting the next blower into operation. When the selector arm of the system 13 moves to the last contact 30 the coil 7 is energized, the contacts 20 disconnect the holding circuits of coils 5, 6, thus opening contacts 17, 19 so that the leads from the bus-bar 34 to the selector 1 are interrupted and the equipment is brought to a standstill.