GB959715A - Control circuit arrangement for electric furnace - Google Patents

Abstract

959,715. Control systems for arc furnaces. BIRLEC-EFCO (MELTING) Ltd. March 7, 1963 [Feb. 22, 1962], No. 6944/62. Drawings to Specification. Heading H2H. [Also in Division G3] A three-phase electric furnace is supplied with alternating current through a tap-changing transformer and the power consumed by the furnace is determined by an induction type watt-hour meter actuating impulses contacts at a rate dependent on the meter rotor rotation. The impulse contacts actuate a " first charge " relay and a " back-charge " relay, the holding times of which are adjusted in dependence on the weights of the charges. The relay controls a motor driving a cam sequentially operating micro-switches selecting the taps on the transformer, so that the angle through which the cam is moved for each impulse is related to the charge-weight. In an alternative arrangement banks of tap-changing uniselectors are arranged so that the uniselectors are stepped between the impulses from the watt-hour meter in dependence on the charge weight. The stepping of the uniselectors is also modified in dependence on the quality of the charge. When power is cut-off from the furnace the heat loss is compensated for by (1) driving the cam in reverse at a predetermined rate, or (2) stepping the uniselectors back at a rate determined by a capacitor delay circuit. The drive to the motor or uniselectois is inhibited when the furnace temperature is above a desired value. The end of the melt-programme is audibly or visually signalled and the arrangement may be manually actuated.