Theoretical and Experimental Evaluation of Hot-spot Temperature at Series Connection of Turbine Generators

During stator rewinding of an air-cooled turbine generator, thermal discoloration of end winding insulation was observed. Measured winding temperatures remained within the class 130 (B) temperature limit, but the discoloration indicated that the local strand temperatures may have been much higher. Previous studies [1][2] showed that the strand temperatures can significantly be higher than that of measurable temperatures; however, those study could not explain the observed discoloration. The insulation degradation was highly sporadic. Some location exhibited severe discoloration while adjacent areas appeared nearly unused. No clear correlation was found with electrical or physical parameters such as voltage, ventilation, or phase shift. All bars and end windings are manufactured by the same…