Continuous Success of DC EAF Power Supplies

Continuous Success of DC EAF Power Supplies
Daniel Sager
Shripad Tambe
Räto Stadler
Rajesh Pai
ABB Switzerland AG,
5400 Turgi, Switzerland
Tel.: +41 58 589 2877
Fax: +41 58 589 2090
E-mail: [email protected]
Key words: Rectifiers, SVC, DC EAF, Electrode Control.
INTRODUCTION
DC power supplies are widely used in the steel and non-ferrous industries – ABB continues to focus on DC technology while
improving safety, reliability, efficiency, maintainability and performance.
With increasing pressure from utility companies to their big industrial customer to be ‘clean’ (low flicker, tighter power factor
requirements and no unbalanced load), DC EAF technology continues to demonstrate advantages over AC EAFs.
As plants with EAF’s are often built close to the mine site, in a rural area far away from the next power station, the utility’s electrical
grid is normally very weak for big industrial consumers (a Minimill easily consumes 400 MVA). In such cases, DC EAF becomes the
ideal answer.
ABB’s new AC 800PEC controller provides optimized current control, features an enhanced electrode control (ELREG) capability
and a fast direct link to the SVC control (ArcComp) in order to achieve shorter power-on-time and higher average power input
resulting in increased production.
This paper discusses the following topics:
1. Silent success of the DC EAF: Why the DC Arc Furnace is still in fashion
2. Advantages of the SVC with DC EAF: Efficient flicker reduction thanks to the Rectifier Control’s direct link with the
SVC Control system
3. Converter types and topologies
4. Reducing losses by using magnetic coupling
5. DC EAF users survey: Some performance data and reasons why Minimills operate with DC EAFs
6. Reducing maintenance costs and furnace downtime with NoArc: Keeping the rectifier transformer energized during
tapping but disconnecting and grounding the furnace on the DC-side leads to increased system availability by
simultaneously reducing risks and maintenance costs
7. ABB’s latest power control system, the AC 800PEC, features a high-speed control for current and voltage (electrode
control), precise status and fault indications, easy integration with the plant’s control network, and very high reliability
8. Optimized current and electrode control: By using ELREG, the software analyses on its own, depending on raw
material conditions and melt progress, the best parameters for current and arc control. Electrode control doesn’t even
need to consider the electrode arm’s physics in order to reduce its mechanical stress
1 Silent success of the DC EAF
Many earlier papers have addressed the numerous advantages of the DC EAF. In summary, the following development was observed
over the last 10 to 15 years: In the early/mid 90s, there were huge expectations for the newly promoted DC arc technology, based on
thyristor rectifiers as power supply, promising better efficiency, better arc control, lower electrode consumption and lower flicker,
while at the same time long life for the furnace bottom anodes and the furnace refractory was expected. As soon as the first success
stories echoed, new ideas for DC power conversion were promoted, such as the chopper technology (converter based on IGBT

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