Heating in transformer cores due to radial leakage flux. Part 1: Experimental models and test results

The heating effects of radial fluxbecome increasingly important in the design of large power transformers, both because of the higher flux densities generally involved and larger dimensions of components affected, particularly the core clamping structure. This paper describes two series of models constructed to study the heating of transformers cores and core clamping structures under the influence of radial leakage flux from the windings. The first series of models was designed to obtain urgently needed design information on the temperatures to be expected in various practical geometries, and their longer-term effect on the insulating materials used in their construction, while the second series was used to allow a more detailed study of flux penetration and eddy-current effects to be made. Formulas for the calculation of the losses and resultant temperature rises are derived and compared with measurements made both on the models and on transformers. The significance of the results for the design, testing and operation of transformers is discussed.