Internal Temperatures of A-C. Generators

The paper deals with the internal temperatures of a number of typical large a-c. generators; this temperature being measured by a thermo-couple placed between armature coils in the same slot and in the center of the core. The difference between these measured internal temperatures and the corresponding surface temperatures in the tests given varies from 0 deg. to 35.5 deg. This wide divergence is explained by the aid of the tests and of calculations. A method of calculation for internal temperatures is given which is based on simple heat laws and on data obtained from many tests. By means of the tests and of parallel calculations, the effect on the internal temperature of changes in frequency, core length, thickness and quality of insulation, armature current density and core densities, is explained. The capacity of the end windings to dissipate heat from the center of the core is also discussed. In conclusion, it is stated that although the wide divergence between surface and internal temperatures of different classes of generators is regular and can be justified, yet it is plain that there is no one average figure that can be used for that difference for all classes of a-c. generators.