| 摘要 |
PROBLEM TO BE SOLVED: To stabilize a power supply network even when the reactive power of an electric system is changed by controlling a transformer by a switching sequence so that the power factor of reference frequency is always equally held at about '1'. SOLUTION: A substance to be melted is supplied to an arc furnace 5 and a 1st electrode 4 and a 2nd electrode 8 formed on a bottom area are connected to an AC network 1 through a transformer 3 and a switching device 2. In the device 2, three phase inputs R, S, T are formed in a control closed loop consisting of three sides and the primary windings 11, 11', 11" of the transformer 3, switching element 10, 10', 10" and free wheel control loops 12, 12', 12" are respectively arranged. In the transformer 3, the high speed switching elements 10, 10', 10" are on/off controlled by a switching sequence for always generating the power factor of reference frequency so that a three-phase sine wave input signal has at least a value of about '1'. Consequently interference reaction on the network can be avoided.
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