THE INFLUENCE OF SUPPLY TRANSFORMER DESIGN ON THE TRANSFORMER CORE DC MAGNETIZATION

The article covers the issues of magnetization of the core for TRDN 63000/110 three-limb core supply transformer and TDT 400000/220 shell-core supply transformer using direct current with the grounded high voltage winding. The authors developed the model of the supply transformer magnetic field in DC magnetization conditions taking into account the electrotechnical and structural steel magnetization curves nonlinearity. The magnetic field modeling in core limbs of supply transformers is performed using the FEMM software by finite-element method. The distribution patterns of magnetic field lines for TRDN 63000/110 and TDT 400000/220 supply transformers were created. The magnetic fields created by DC in the TRDN 63000/110 supply transformer with three-limb magnetic structure cannot complete through transformer magnetic core and replace each other completing partially through the supply transformer trunk and its airspace. The research showed that the supply transformers with shell-core magnetic structure are capable to complete lines of force within the magnetic system that increases considerably the core DC magnetization intensity. The authors built the dependences of average values of magnetic induction in the center cross-section of limbs of magnet on DC value. Obtained dependences make it possible to estimate the influence of direct current on the value of average magnetic induction and the velocity of saturation of the supply transformer magnetic system and to make a conclusion that TRDN 63000/110 supply transformer is subject to the direct current component impact to a lesser extent in comparison with TDT 400000/220 supply transformer due to three-limb design of magnetic system.