Magnetizing current measurements on full scale power transformers

Abstract

The magnetic properties of a power transformer core are generally held to be quite similar to those of the core steel itself. Due mainly to it being rare and practically difficult to acquire a transformer for testing and verification, testing of large units is usually only performed concerning no-load losses. However, other parts of the magnetic hysteresis loop are more sensitive to variations in material and geometry and could be used for more detailed diagnostics. This paper shows that measurements of magnetic hysteresis can be performed with good results on large power transformers. Methods to compensate for capacitive currents and to calculate the effective magnetic length of the core are shown and the results are compared to standard material measurements. The results show good agreement with Epstein frame measurements on annealed samples.