Željko Štih

Local overheating of transformers with high currents

Purpose – The purpose of the paper is to compare losses and temperatures in power transformer tanks for different high current lead arrangements. Design/methodology/approach – 3D computational tools MagNet and ThermNet based on the finite element method are used to calculate magnetic field distribution in 3D models of power transformers. Eddy current losses in conducting metal parts are induced by the stray magnetic field of transformer windings and high current leads. From loss distribution and appropriate cooling condition temperature values are calculated. Findings – From calculation results it is possible to understand advantages and disadvantages of different lead arrangements. The analysis is finalized with a short presentation of the influence of magnetic shielding height on temperature and loss values. Originality/value – Results give transformer designer clearer understanding of precautions that should be taken for avoiding high temperatures on the tank wall of a transformer.

Fully Coupled Dynamic Model of Thomson’s Levitating Ring

The complete electromagnetic-mechanical-thermal modeling approach is demonstrated on the Thomsons levitating ring experiment. This problem, but with a different set of parameters, was also described by Laithwaite and defined by Freeman and Lowther as TEAM17 problem. This paper presents its most complete solution. The factors for determining the vertical displacements and influence of the height of the ring are explained. The whole apparatus is explained in detail so that an accurate computer model can be made. The model introduced is validated against measurements and transient finite-element method (FEM) solvers. All the results prove the applicability of using steady-state FEM analysis with lumped parameter approach for a fast and effective fully coupled modeling.