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CONTACT SHOE WISE CURRENT MEASUREMENT IN A SUBMERGED ELECTRIC ARC FURNACE – PROCEDURE, ADVANTAGES & LIMITATIONS
Bhabesh Kumar Mohanty1
1ArcelorMittal Nippon Steel, Barbil, India

PAPER: 197/Iron/Regular (Oral) OS
SCHEDULED: 17:50/Mon. 21 Oct. 2024/Ariadni C

ABSTRACT:

In a submerged electric arc furnace, contact shoes/ clamps/ pads are large copper/ copper alloys components, that are pressed against the electrode casing to conduct electric current into the electrode from the furnace transformer/s connections. Submerged electric arc furnaces normally use Soderberg electrodes in which the solid electrode paste becomes molten and then baked to solid by the increasing heat as the paste moves down inside the electrode casing and passes by the contact shoe area. To bake the paste properly and uniformly across the cross-sectional area of the electrode, the appropriate level of current and its uniform distribution among all the contact shoes of the same electrode, are required, to provide the heating, to solidify the electrode paste at the correct rate. Lower current level at any contact shoe may result in poor baking in the zone of that contact shoe, which may force to reduce the slipping rate to prevent the baked paste level dropping too below the electrode contact shoes or it may result in a green break in extreme case. The contact of the contact shoe with the electrode is not fixed, as the electrode must be supplemented from the top, which continues to get consumed at the bottom; this makes the working conditions of the contact shoes worse. Contact shoes are designed for long and trouble-free operation with optimum electrical contact. Also, to avoid hot spots around the contact shoes or overloading of any contact shoe, the equalization of current in each contact shoe of an electrode is essential. High unequal contact shoe current may indicate poor contact shoe service pressure, over slipping of the electrode so green electrode beneath the contact shoe, furnace zone wise charge mix problem/ under carbon, electrode breakage, issues with the transformer secondary winding, cooling circuit problem of that contact shoe, electrode casing problem, cavitation in the electrode, arcing of contact shoe, double earthing issues etc. This paper focuses and describes the procedure for accurate measurement of individual contact shoe current as well as accurate derivation of electrode-wise current and furnace transformer phase wise current; so that from the recorded trends the above noted problems can be predicted and longer breakdown for defective contact shoe replacement can be substituted with no required replacement / planned maintenance, resulting in higher availability and more efficient operation.