Abstract
Startup fuses are used to protect cathode busbars from arcing damage when putting a cell in circuit. While an ideal fuse would divert all electrical current flowing through a given short-circuiting station when removing its last wedge, this is never the case in an operating cell. Fuses are part of a parallel network of conductors, therefore, the amount of current effectively diverted depends not only on their dimensions, but also on pot internal resistance at the preheating phase and on the interfaces electrical contact resistance. This article discusses the physics of startup fuses and the on-duty behavior of both bolted-on-bus and clamped specimens. Prototypes were designed using numerical analyses and then field-trialed at different amperages. Apart from validating numerical predictions, experimental data indicated that fusing time may be directly estimated by pot voltage readings, if sampled raw and at high enough frequency .
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Notes
- 1.
Which can be readily verified by means of cathode ring-to-wedge electric potential measurements : virtually the entirety of the voltage drop between the two opposed SCS halves, ΔVsts, occurs at the busbar -to-wedge contact interfaces.
- 2.
About two orders of magnitude larger than that of a permanent cathode ring busbar .
- 3.
Or in the case of a potline restart , i.e., when there’s no current flowing through the pot-to-pot busbars.
- 4.
From last wedge removal to fuse failure, when (∂Tfuse∕∂t) is maximum.
- 5.
Unless the fuse is sufficiently long thus allowing one to neglect both the effects of heat conduction to SCS and local heat generation at the constricted section.
- 6.
And, in the limiting case, not failing at all.
- 7.
Given that Rwedge continuously increases as each one of these jumpers is disconnected, more current is diverted to Rfuse each time—refer to Fig. 1.
- 8.
Estimated from ΔVpot = f(t)—right hand side of Fig. 8—and Ioper = f(t), as recorded by the pot control system.
References
A. Al Jasmi, A. Zarouni, L. Mishra, M. Batski and V. Potočnik, “Concept and Design of Dubal Pot Start-up Fuses”, Proc. Light Metals 2014, TMS, Warrendale, PA, pp 729–732.
A.F. Schneider, D. Richard and O. Charette, “Impact of Amperage Creep on Busbars and Electrical Insulation: Thermal-Electrical Aspects”, Proc. Light Metals 2011, TMS, Warrendale, PA, pp 525–530.
Acknowledgements
The authors would like to genuinely express their gratitude to the following people, whose invaluable contributions made this work possible: Marc Hamelin, Claude Moisan, Marc Denis and Francis Isabelle from ALCOA Operations, René Trudel from ALCOA’s Aluminum Center of Excellence and Lou Malenfant from Charl-Pol, Inc.
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© 2019 The Minerals, Metals & Materials Society
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Schneider, A.F. et al. (2019). Thermoelectrical Design of Startup Fuses for Aluminum Reduction Cells. In: Chesonis, C. (eds) Light Metals 2019. The Minerals, Metals & Materials Series. Springer, Cham. https://doi.org/10.1007/978-3-030-05864-7_76
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DOI: https://doi.org/10.1007/978-3-030-05864-7_76
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