Analysis of DC electric arc furnace electrode control system and its improvement

In DC electric arc furnace steel-making in the refining process, melting, melting, its initial stage of oxidation and reduction on power supply (voltage, current) have different requirements, energy efficiency, improving efficiency, achieve the best technical and economic indicators.

And communication control method of electric arc furnace steel-making does not, arc voltage of DC electric arc furnace (ARC voltage) and the arc stream (the arc current) size is two entirely independent conditioning system control, arc voltage and arc current can be adjusted independently of automatic linearly, to meet the requirements of smelting technology for power supply. ARC stream regulating system of thyristor rectifiers as regulation, automatic closed-loop stability of arc current flow regulator control thyristor rectifier output DC current, under static conditions, auto-steady flow system can maintain a constant arc flow unchanged. In the context of effective control, arc arcs caused by pressure changes do not flow with the change, which create the conditions for independent and adjust the arc length arc voltage. DC arc furnaces in steelmaking process, electrode lifting control system for electrode positioning mechanism for controlling object, whose primary role is to adjust the length of the arc column (ARC length). In accordance with the relevant documentation analysis, Va the arc voltage and arc length approximation between La and there is the following relationship:

Ka=0.6~1.1V/mm call in an arc voltage gradients, pressure gradient varies, depending on the size of the arc furnace atmosphere. Relative to the arc current and arc voltage rate of change, believing that Ka values change very slowly, can be approximated as a constant. Thus, arc voltage and arc grew up to be an approximate linear relationship. Adjust the arc length is equivalent to adjust the length of the arc voltage of high and low. When the arc when the stream is constant, adjust the arc length is equivalent to adjust the arc power level. ARC power Pa=IaVa. So, have a direct impact on the performance of the electrode lifting control system of electric power input and the furnace running.

2 the main problem and cause analysis

Gansu Tibetan metallurgical group special steel two nominal capacity of 5 tons of DC electric arc furnace steel-making in 1997 and began to put into trial operation, commissioning and discovered electrode lifting control system is not working properly, exists mainly in the form of:

(1) is not stable, electrode flees the frequent and of long duration, the arc furnace without continuous and stable access to effective power input;

(2) arc down, fifth tranche with the highest AC voltage, arc voltage (DC) values will only be around up to 250V, severely limiting the arc power increase, network side of transformer power factor is relatively low;

(3) the arc voltage adjustment range is small, real arc voltage values not follow change linearly with the given arc voltage values. Control of smelting technology of performance does not meet the requirements, do not accurately on stabilization of arc voltage at a given value of;

(4) circuit high failure rate, frequent power outages, maintenance, adjustment, or replace components, seriously impacting production. <br> according to the problems that occur in the course of trial run, after careful on-site observation and careful analysis of control circuit system, that occurs above the main cause of the problem has the following aspects: