Calculation of the Magnetic Field and Inrush Current in a Three-phase Transformer

When a power transformer is connected to the grid, the inrush current increases substantially with a high value of harmonic components. At that time, the amount of flux in the core increases causing the magnetic circuit to saturate with a duration up to many grid cycles. This may cause malfunction of protection relays or interfere the operating condition of nearby electrical instruments. Therefore, it is important to analyze the phenomenon of the inrush current and the magnetic field inside the transformer. This paper has derived a simulation model for three power transformers with capacity of 250kVA, 1500kVA and 2200kVA by using Ansys Maxwell 3D software when connecting the transformers to power grid under no load condition. The winding voltages, the inrush currents, and the flux density inside the core of each transformers have been analyzed. Furthermore, with the help of the finite element method, the overvoltage and/or overheating phenomenon of transformers can also be studied.