Thermoelectrical Design of Startup Fuses for Aluminum Reduction Cells

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.