Calculation of the flux distribution of three phase five limb power transformers considering nonlinear material properties
Purpose - Depending on the load the flux-density distribution inside power transformers core shows significant local variations due to stray fluxes which enter the transformer core. As saturation of the core has to be avoided the flux-density distribution has to be determined early in the design stage of the transformer. This paper seeks to address these issues. Design/methodology/approach - To determine the load dependent flux-density distribution the operating point of the transformer is calculated considering linear and non-linear material properties. The operating point is determined using a linearised lumped parameter model of the transformer under various load conditions. Considering non-linear material properties the inductance matrix depends on the operating point and will be extracted by means of the FEM whenever the magnetic energy within the transformer changes notably. Findings - This paper presents a numerical stable approach to calculate the operating point of a transformer by using the magnetic flux linkage as state variable for the coupled field problem. Research limitations/implications - The proposed approach uses a fixed time-step to update the lumped parameters by means of the FEM. This results in long simulation times. In further research it is planned to implement an adaptive time-step method based on the change of the magnetic energy. Originality/value - A numerical stable approach to calculate the operating point of a transformer by using the magnetic flux linkage as state variable for the coupled field problem is proposed. The methodology is applied to a 2D model of a three-phase transformer. However, it also can be applied to 3D FE models. Based on the calculated operating point, the flux-density distribution can be determined and several post-processing methods can be executed (e.g. determination of core losses, ... ).
fluxes transformers flux-density distribution field circuit coupling load dependent stray fluxes transformer core saturation phase shifting transformer flux density