Electrical energy consumption accounts for 30 to 40 per cent of the cost of aluminium production. This paper describes and intends to discuss the commonly used electrical power quality compensation concepts and designs as well as the potential of operation cost reduction which a high electrical power quality can have. Power quality is assessed by the "harmonic currents" still in the feeding power grid after cleaning them up and "power factor" when the smelter is running under normal conditions. Looking at a large 2 pot line smelter, at least one additional power generation unit is required if no power factor and harmonic current compensation system is installed. The investment cost for one additional power generation unit and the yearly operation cost have no relation whatsoever to the investment cost for a compensation system. Harmonic currents create electrical losses and if not compensated create costs for additional electrical power. These additional costs for electrical power pay off the investment cost of the compensation system in a very short time. Compensation systems connected to the power grid require detailed studies and a high number of parameters need to be known or made available by the power utility. When installed and operated on the grid the power utility will normally ask to control them as they are connected to their grid. Their drawback is that should the feeding grid get polluted by other consumers during the years to come, they will be loaded with this power quality pollution. Compensation systems connected to tertiary windings of the regulation transformer are decoupled from the grids and are less affected by power quality pollution coming from the grid or which already exists in the grid. Both compensation concepts eliminate the need for additional power generation units which cost many times the initial cost of a compensation system, or additional cost for electrical power due to electrical losses created by poor power quality.
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