Characterization of Magnetic Losses in the Transformer Tank Steel

The transformer tank is normally built of construction steel and has relatively large thickness of 1.2 mm for distribution up to 12 mm for large power transformers. In such thick materials, skin effect becomes much more significant than thin materials due to both frequency and non-linearity. The flux density in the tank can vary in a wide range of some mT to 1800 mT (in the case of having high zero sequence flux) leading to a large variation in the permeability and, consequently, in skin depth. Since the losses are high, the temperature rise can also be a main problem influencing the conductivity that must be considered in the loss calculations. The main contribution of this paper is to study the magnetic losses in the transformer tank steel through the measurements and finite difference-based numerical calculations. Using the loss separation principle, different loss mechanisms are investigated, and the behavior of each at the different level of inductions and frequencies is studied.