Electric Arc Furnace

1. EAF Introduction
2. Developments in EAF Technology
3. Basic Equipment and Operation
4. Furnace Layout
5. Electrical Equipment
6. Melting
7. Burners
8. Raw Materials
9. Raw Materials Preparation
10. Alloy Yield
11. Electrode Breakage
12. Slag Foaming
13. Slag Foamability
14. Slag Reduction
15. Deslagging
16. Tapping
17. Exercise: EAF Operation
18. EAF Simulation

The electrical power system consists of a primary and secondary side. The primary side is the high voltage side feeding the steelmill furnace from the plant sub-station.

The primary side, with a voltage of 25-50 kV, enters a furnace transformer where the voltage is decreased to a level suitable for the furnace operating conditions (secondary side), normally between 400-1000 V. In the case of alternating current, three phases are used and three electrodes will be needed. Each of the three phases is connected to one of three graphite electrodes.

The graphite electrodes play an important role since they carry the electrical power into the furnace. Graphite material is used because it withstands high temperatures and is a good electrical conductor. When the electrode is near the scrap an arc is created and an electric circuit is formed. These arcs provide the heat energy needed to melt the scrap – the higher the voltage, the longer the arc. The aim is to always have an even uptake of the provided power. Thus the electrodes have to be raised or lowered depending on the voltage reading.

Operating an EAF requires careful monitoring of the furnace electrical parameters at all times. By adjusting the tap settings, i.e. the pre-defined combinations of voltage and current, the electrical characteristics may be altered in order to fit the present operating conditions.

The electrodes have an upper limit in maximum current allowed, which in practice leaves the secondary voltage as the main regulating parameter when changing tap setting. The secondary voltage is directly proportional to the arc length inside the furnace.