Helmut Schmidt University (Hamburg, Germany):

Schnack H., Mag. Eng., e-mail: schnack@hsu-hh.de
Krüger K., Dr. Eng., Prof., Technological Data Processing and System Analysis

Maschinenfabrik Rheinhausen GmbH (Regensburg, Germany):

Babizki A., Mag. Eng.
Wu J., Dr. Eng., Net Integration Group

In a joint research project, Maschinenfabrik Reinhausen GmbH and Helmut Schmidt University develop a control algorithm for AC-EAF based upon a solid-state tap changer (OLTC) for electric arc furnaces. Through this tap changing method it will be possible to flexibly vary the arc current within 20 ms intervals. The OLTC operates within the possible switching stages, changing the secondary line-to-line voltage. Through this technology it is possible to reduce grid voltage fluctuations (flicker) resulting from overcurrents and undercurrents. In addition, a significantly calmer operation of the three phases offers possibilities to reduce electrode consumption and to dam mechanical loads in the high current system. Especial attention has been paid to development of recognition algorithms providing forecast of variation of current load in the nearest 10 or 20 ms and to ignore retarding time that is usual for thyristors. Additionally, possibilities of control of the asymmetric working point are expanding due to adjusting of transformer stages along separate winding turns. Stable burning of the electric arc and direct decrease of return effect on the net can be achieved. It is concluded that qualification testings for efficiency confirmation are strictly required.

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