| 摘要 |
<p>PURPOSE:To improve a power factor in an electric power supply device while maintaining the progress of melting of metal to be melted by means of an arc. CONSTITUTION:A maximum variation of arc voltage to preset voltage is detected from a signal of a voltage detector 12 by means of a voltage variation operation part 16. In a period when an electric current of not less than 50% of a value preset by means of an electric current setting unit 14 is detected to prevent erroneous detection by means of a signal of an electric current detector 13, signal data of the voltage detector 12 are gathered. The data are gathered for a fixed time (several seconds-several minutes) with every constant period, and preset voltage is subtracted from a maximum data value during this time, and the maximum variation of the arc voltage to the preset voltage is detected. Maximum usable voltages of respective taps and the sum of the maximum variation of the detected arc voltage and a preset voltage value are compared with each other, and a secondary voltage tap of a transformer is selected according to the maximum variation of the arc voltage.</p> |
