Regulating arc in metal melting, welding or plasma process - includes using second order differential of arc current w.r.t. time as regulating parameter

摘要

Regulation of the arc of metal-melting arc furnaces, welding units or plasmas involves adjusting the electrode distance from the material being melted in accordance with the value obtained by double differentiation w.r.t. time (i.e. d2I/dt2) of the arc current between the electrode(s) and the material during arc operation. In the case of an arc melting furnace, pref. the method involves (i) summing the instantaneous values of the phase voltages of the electrodes; (ii) summing the values of the rectified phase voltages; (iii) calculating the difference between the two sums; (iv) subjecting the transformer output current to second order differentiation w.r.t. time; (v) comparing the value from (iv) with the previously determined value for the max. melting rate (wt./time); and (vi) forming a signal for electrode stand-off distance regulation from the value obtained in (iii) and from the comparison (v). ADVANTAGE - The second deriv. of the arc current w.r.t. time is directly proportional to the melting efficiency (melted wt. per unit time) and can thus be used for direct regulation of melting power or plasma power to give considerably increased yield.