Water Chemistries of an Electrical Generator Cooling System

Abstract

At some thermal and nuclear power plants, water is used for cooling the electric generator stator windings with copper used as their main structural material. During operation of such cooling systems, certain problems are encountered as a consequence of copper corrosion and deposits formed on the inner surfaces of stator winding cooling channels. Inadequate quality of water circulating in the tubes is one of the factors causing the corrosion to occur. The article outlines the main stages of the corrosion and deposit formation processes: copper surface oxidation with formation of copper ions, formation of oxides on the metal surface, partial transfer of oxides from the metal surface into water, and carryover of oxides from one metal surface area to another. Four basic water chemistries for electric generator cooling water systems developed by the International Association for the Properties of Water and Steam (IAPWS) are discussed. These water chemistries are based on using low-oxygen (20–50 μg/dm3) and high-oxygen (2000 μg/dm3) treatments. The article gives the basic standardized and monitored indicators characterizing the water quality in electric generator cooling systems for the water chemistries developed by the IAPWS. Apart from the water chemistries described in the IAPWS technical document, the article presents data on the advantages of using reducing agents for cooling water treatment, e.g., hydrogen in concentrations ranging from 30 to 60 μg/dm3.