Calculation of the flux distribution of three phase five limb power transformers considering nonlinear material properties

Abstract

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, . . .).

Multi-harmonic approach to determine load dependent local flux variations in power transformer cores

“…The inductance matrix is extracted systematically from a Finite Element model of the transformer by means of static simulations in the time domain based on the magnetic energy. The method to extract the inductance matrix is described in detail in [4]. The working point of the transformer, considering nonlinear core material, is determined as depicted in the flow chart in Figure 1.…”

“…The computational effort decreases significantly for the multi-harmonic approach. The computational effort of the multi-harmonic approach is approximately 30 minutes (w/o parallelisation), whereas the effort of the time-stepping method is more than 2 days, due to the transient phenomenon [4]. …”

Improving Core Quality in Power Distribution Transformers Using Machine Learning Methods

“…Predicting iron losses of individual cores is a critical problem in an industrial setting that deals with the transformers with wound cores for distribution built since these losses have a substantial impact on both the quality and functionality of the resulting three-phase power transformers. Additionally, core expenses account for around 30% of the total power transformer material cost (Riemer et al, 2013). In fact, it would be ideal if individual core iron losses could be predicted in the early stages of core production because it would allow for potential corrective steps to be taken while the manufacturing process is still ongoing.…”