GB1215721A - Electrode control systems for electric arc furnaces - Google Patents

Abstract

1,215,721. Automatic arc furnace control. ALLEGHENY LUDLUM STEEL CORP. Nov.17, 1967, No.52526/67. Heading G3R. A polyphase arc furnace has its electrodes positioned by a circuit responsive to the time averaged value of arc power. Each electrode e.g. 16 has signals proportional to arc voltage and current passed to units 80, 38. For constant power a signal proportional to power applied across a resistor 84 is compared with that across a reference potentiometer 94, the error being passed to units BSI, BSR, which adjust the electrode position through a servomotor system. By a switch (128) Fig.4 (not shown) the electrode spacing may be alternatively controlled by power factor through units BSHPF, BSLPF which similarly adjust the electrodes. The circuit may be arranged under power control when the power factor is within a range of values or power factor control outside this range. Potentiometers 104, 106 provide opposing currents to provide band width control and electrode power loss compensation respectively. The circuit may be controlled by any known programme arrangement, which may be coupled to controls 94 (128). In Fig. 1 (not shown) a signal proportional to power is compared through an averaging circuit (42) with a signal proportional to current so that electrode may be moved in an appropriate direction. A circuit comparing power change relative to current change may alternatively be employed. The power factor is separately controlled by adjusting the taps, off load, on a transformer feeding the furnace. The taps may also be adjusted if the range of circuit adjustment does not produce the desired power consumption. A low arc voltage short circuit detector 74 is provided which retracts the electrodes.