TL;DR

Arc instability is most often caused by a worn or broken electrode, or contact arm current path deterioration. Inspect the electrode condition and the contact shoe contact before adjusting any controller parameter.

What you might see

arc flicker visible on the power trace
electrode current fluctuating widely
ladle heating rate below target
electrode position controller hunting

Likely causes

Tap to mark as ruled out

Electrode crack or partial break reducing the current cross-section
Contact shoe worn, leaving poor electrical contact between the arm and the electrode
Scum and slag floating on the bath surface creating arc instability
Power bus or flexible cable connection loose or corroded

Required tools

Aluminized radiant-heat PPE
Insulated torque wrench for power terminals
LOTO kit for transformer isolation

Safety first

Extreme thermal radiation from the open ladle furnace. Aluminized PPE is mandatory near an open ladle.
High-voltage power circuit on ladle furnace electrodes. Only qualified personnel with proper permits may work on the power circuit.
Molten steel splash hazard if electrodes contact slag or bath surface violently. Keep clear of the ladle perimeter.

Procedure

6 steps · ~45 min

1
Stop the heating process and wait for the electrodes to retract to the safe upper position.
Warning: Extreme thermal radiation from the open ladle. Use aluminized radiant-heat PPE and maintain maximum safe distance when working near an open ladle.
2
Visually inspect each electrode from the platform for cracks, breaks, or eccentric wear on the lower stub.
3
Inspect the contact shoe clamps for wear and clean any scale or oxidation from the contact surfaces.[1]
4
Check the flexible power cable connections at the contact arm for looseness or heat discoloration. Tighten any loose terminals.
Warning: All electrical work on ladle furnace power circuits requires isolation from the transformer and an Energized Electrical Work Permit for any energized checking.
5
If the steel bath has excess slag, adjust the bath chemistry to reduce scum before continuing heating.[1]
6
If arc instability persists after electrode and contact shoe inspection, review the electrode regulator controller parameters with the furnace control specialist.

Sources

Danieli Danieli LF Ladle Furnace / AOD / VOD general technical documentation, Danieli
Danieli ladle furnace operation and maintenance documentation, electrode and contact arm inspection procedures (general)

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