Calculation of circulating currents in transposed conductors of transformer windings

V magistrskem delu smo obravnavali glavno in stresano magnetno polje v močnostnem transformatorju. Obravnava stresanega magnetnega polja je ključnega pomena, saj lahko z ustreznim načrtovanjem zmanjšamo končne ohmske izgube transformatorja. Neenakomerna porazdelitev stresanega magnetnega polja vpliva na porazdelitev tokov v transponiranih vodnikih transformatorskega navitja. Preverili smo, kako na porazdelitev tokov vplivajo geometrija sekcij navitja, geometrija kablov in hladilnih kanalov ter upornost navitij. Izračun porazdelitve tokov smo izvedli s pomočjo programskega orodja OCTAVE, s katerim smo preko vmesnika in z uporabo skriptnega jezika Lua krmilili FEMM (Finite element method magnetics). V programu FEMM smo izrisali navitja in transformatorsko okno, ki je predstavljalo meje obravnavanega problema. Navitju smo preko avtomatiziranega programa v OCTAVE določevali smeri tokov, dokler nismo pridobili podatkov stresanih magnetnih energij vseh možnih parov navitij za nadaljnji izračun. Na osnovi analize smo prišli do zaključka, da bolj kot je enakomerna in nižja kot je stresana magnetna energija v navitju in med navitji, enakomernejša je porazdelitev tokov v navitju in s tem nižje končne izgube transformatorja.This thesis is focusing on the main and leaked magnetic field in a power transformer. Dealing with a leaked magnetic field is crucial because the proper design of windings can reduce the final ohmic losses of the transformer. The uneven distribution of the leaked magnetic field Wm affects to the distribution of currents in the transposed conductors of the transformer windings. We examined how the flow distribution is influenced by the geometry of the winding sections, the geometry of the conductors and the cooling channels, and the resistance of the conductors. The flow distribution was calculated using the OCTAVE software tool, which controlled the FEMM (Finite element method magnetics) via the interface and using the Lua scripting language. However, through the automated program in OCTAVE, we drew, windings and bounderies of the problem that was taken under consideration and determined the directions of currents through the automated program until we have obtained the data of the leaked magnetic energies of all the possible pairs of windings for each further calculation. According to this analysis, we concluded that the more uniform and lower the magnetic flux in the winding and between the winding is, therefore it balances more the current distribution in the winding and reduces the final losses of the transformer