Modified electrolysis cell and a method for modifying same

A method for reducing the metal pad unevenness and optimizing the MHD stability in an electrolysis cell of the Hall-Héroult type for aluminium production, the cell having suspended prebaked carbon anodes and a cathode panel comprising several carbon based cathode blocks having one or more collector bars thus forming a cathode block assembly, where said cathode block assembly may be constituted by several individual cathode block sections that together with its cathode collector bars form cathode block section assemblies, the cell further having a metal pad that lies onto the cathode panel and an electrolytic bath between said metal pad and the anodes, where unevenness of the metal pad is detected by measurements or calculations,

• wherein
• a model of the electrolysis cell is established in a computer based modelling program where each cathode block assembly or cathode block section assembly is represented, the modelling program being able to identify which cathode block assembly or cathode block section assembly that preferably should be modified, where at least one of the modifications is implemented in the cell by changing selectively the electrical current distribution in individual cathode block assemblies or in cathode block section assemblies so that the local electrical current paths and correspondingly the local forces in the metal above the cathode panel are modified to reduce the unevenness of the metal pad and optimize the overall MHD stability of the cell.