Keeping Your Stator Cool
By David G. Daniels
Water-cooled stators can become fouled with copper oxides that limit flow through the stator bars, causing elevated temperatures that can restrict or shutdown a unit. Methods have been developed for off-line and on-line chemical cleaning of these systems with ethylenediaminetetraacetic acid (EDTA). This article will review why chemical cleaning is needed, typical procedures and parameters that need to be monitored during the cleaning to make the cleaning successful, and cleaning up the system after the copper removal is complete.
It is s important to understand that throughout the stator bars that the copper strands, including the hollow strands that transport stator cooling water, change position within the bar. For example, hollow strands for cooling water flow may be in the top right-hand corner of a stator bar on one end and come out somewhere in the middle of the stator bar on the other end. These changes in position of the strands in a single bar are referred to as “Roebel transposition”, and are done to reduce circulating electrical currents in the stator bars. In addition, there are always multiple elbows and bends found at the ends of the stator bar.
The narrow passages, bends, and twists in the hollow copper strands, including those caused by the Roebel transpositions, create many places for small amounts of mobile corrosion products to partially or completely block the cooling water’s path, causing the stator bar to overheat.
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