Turbine Generator Stator-Winding Temperatures at Various Hydrogen Pressures [includes discussion]

The power industry has for years accepted certain general principles upon which temperature limits are based in the rating of electrical machines and apparatus. AIEE Standard No. 11 sets forth the philosophy to be followed in selecting the permissible total temperatures at various locations within machines, dependent upon the class of insulation employed. The particular values of allowable temperatures and the locations at which they shall be measured in cylindrical rotor machines are stated in the American Standards Association Standard (ASA) C50.2 Both of these standards established their recommendations many years ago, when turbine generators were all air-cooled machines and the industry´s experience on the performance and life of such machines was a dominant factor in the selection of allowable temperatures. In 1937, when turbine generators began to be hydrogen-cooled, the allowable temperatures established for air-cooled machines and the temperature differences between the measurable temperatures and the hot-spot temperatures were tacitly assumed to be correct for the new type of cooling at a hydrogen pressure of 1/2 pound per square inch gauge (psig) in spite of a load increase which was realized with hydrogen cooling. With time, the practice of operating machines at hydrogen pressures higher than 1/2 psig has become quite general. Also for some years a number of machines have had their ratings based on capacities associated with increased hydrogen pressures, and there is no industry standard which recognizes the proper allowable measurable temperatures and temperature rises.