METHOD OF CONTROLLING THYRISTOR RECTIFIER DEVICE OF DC ARC FURNACE

摘要

PROBLEM TO BE SOLVED: To reduce gradually a short circuit current even when short circuit occurs between electrodes by correcting a firing angle of a thyristor with a corrected value of the firing angle equivalent to an increase rate value when an increase rate per unit time of an electrode current exceeds a specified value. SOLUTION: An increase rate computing element 41 is used to compute an increase rate per unit time I from an electrode current. A corrected value arithmetic operation circuit 42 specifies a firing angle corrected value to be zero within the range of the increase rate I from zero up to I1 and increases the firing angle corrected value from I1 to I2 . When I is larger than I2 , an arithmetic operation is made where the firing angle corrected value is used. Furthermore, the firing corrected value is added to a firing angle command value by means of an adding computing element 43. When the increase rate I exceeds a predetermined value of a setting apparatus 45, a timer 46 is started by a comparator 44, which outputs a holding command. In other words, a holding circuit 47 is arranged to hold an immediately preceding value of the adding computing element 43. This value is output to a firing angle controller 48, thereby controlling a thyristor rectifier device.