Load tests on transformers

The paper discusses the different recognized methods of conducting load tests on more than one transformer without applying actual load, also methods of making such tests where one single phase transformer only is available. The actual loading of transformers for test purposes is very expensive, and therefore, the motor-generator method is most suitable whenever more than one single-phase transformer or any number of three-phase transformers are considered. The load and excitation is applied to the high voltage or to the low voltage windings depending upon the rating, etc. of the transformers. When one unit only is available a heat test may be made which consists in applying intermittently an over-voltage core loss with an over-current impedance loss. Approximate values of temperature only are obtained by a combination of an ultimate open-circuit heat run followed by an ultimate short-circuit heat run, and should be used only where not expedient to use the other method. Tables 1 to 8 inclusive show results of the above methods on different transformers as compared with dead load and motor-generator methods. Upon the characteristics of the transformer will depend the over-voltage and over-current for the intermittent runs, so as not to injure the transformer and also to eliminate errors. All the motor-generator methods, Figs. 1 to 6 inclusive, are standard and therefore have been recommended. When one single-phase transformer is considered, the intermittent run method is recommended and this method may be modified so as to obtain a closer refinement.