Interlaminar Flux Density Distribution at Joints of Overlapping Stacked (original) (raw)
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Journal of Magnetics
The design of joints in a transformer core significantly affects the transformer's efficiency. Air gaps cause variations in the flux distribution at the joints of the laminations, which depend on the geometry. Two similar samples consisting of electrical steel strips and amorphous ribbons were made. The spatial flux distributions were determined using an array of search coils for each sample. 2D models of these samples were created and examined by finite element analysis. The magnetic flux distribution for each lamination in the samples was computed. The results show that the flux density in amorphous ribbons above and below the air gap starts to approach saturation at lower flux density levels than for electrical steel. The flux density measured using the search coil under the air gap is increased in amorphous ribbons and decreased in the electrical steel with increasing frequency.
IEEE Transactions on Magnetics, 2000
The paper develops an efficient computational method for establishing equivalent characteristics of magnetic joints of transformer cores, with special emphasis on step-lap design. By introducing an equivalent material, the method allows the real three-dimensional structure of the laminated thin sheets to be treated computationally as a two-dimensional problem and enables comparative analysis of designs. The characteristics of the equivalent material are established by minimizing the magnetic energy of the system. To verify the proposed approach, a series of experiments have been conducted. First, the anisotropic characteristics of the step-lap were established, and then space components of the flux density at specified positions measured. This enabled detailed analysis of the flux distribution in the step-lap region, in particular the way in which the flux travels between the laminations close to the air-gap steps. Encouraging correlation between the homogenized 2-D model and experiment has been observed.
Sensors
The structural discontinuities in the form of air gaps in transformer cores cause the concentration of electromagnetic force, which is an important source of transformer vibration and noise. In this paper, an engineering model of magnetic flux density and electromagnetic force density on transformer core discontinuities is analytically developed. Based on a reasonable structural simplification and assumptions, magnetic flux density and electromagnetic force density are deduced as explicit functions of the geometric, material, and electrical excitation characteristics of the gap region and the transformer core. The accuracy of the established model is validated by the finite element method (FEM) combined with a magnetic measurement experiment. According to this engineering model, the electromagnetic force density can be reduced by decreasing the gap ratio and increasing the gap thickness to a reasonable level. The outcome of this paper can help to understand the physical mechanism of...
Experimental and Numerical Analysis of Shorted Interlaminations in Transformer Cores
— This paper presents an experimental and numerical analysis regarding shorted electrical steel laminations of core of a small transformer core (120 VA single-phase shell-type transformer). Experimental tests were performed to measure the core losses of the transformer with and without shorted electrical steel laminations. Soft solder was utilized to produce the shorted region in the transformer core. Furthermore, 3-D Finite Element (FE) simulations were carried out to compute the eddy current losses in the core of transformer with shorted electrical steel laminations. The laminations of the core and their insulation were taken into account in the transformer model. Finally, several FE simulations were performed to calculate the eddy current losses for several cases, where the location and size of the shorted lamination region was varied in the core of transformer.
IET Electr. Power Appl., 2010
Simple equivalent permeability and reluctance models are obtained for the transformer core joints from the analysis of the magnetic flux. It is shown that the flux variations in the joint zone can be fitted with simple Gaussian expressions suitable for transformer design purposes. These models are derived from 2D and 3D finite element simulations. The magnetic flux distribution in the transformer core joints is studied for wound cores and stacked-lamination cores with step-lap configurations. The models of the study properly account for the effects of core design parameters such as length of air gaps, number of laminations per step and overlap length. The proposed models, which include saturation and anisotropy, are applied to grain-oriented silicon steel (GOSS) and super GOSS. The new models are intended to estimate, right from the design phase, the magnetic flux density, permeability and the reluctance in the joints. The maximum differences between the Gaussian models of this study and finite element simulations are under 6%. The models of this study can be used to improve core designs with the aim of reducing core losses and magnetising current. A comparison of the total losses computed with the model of the study and measurements on a wound core distribution transformer showed differences of about 2.5%.
Modelling transformer core joints using Gaussian models for the magnetic flux density
Simple equivalent permeability and reluctance models are obtained for the transformer core joints from the analysis of the magnetic flux. It is shown that the flux variations in the joint zone can be fitted with simple Gaussian expressions suitable for transformer design purposes. These models are derived from 2D and 3D finite element simulations. The magnetic flux distribution in the transformer core joints is studied for wound cores and stacked-lamination cores with step-lap configurations. The models of the study properly account for the effects of core design parameters such as length of air gaps, number of laminations per step and overlap length. The proposed models, which include saturation and anisotropy, are applied to grain-oriented silicon steel (GOSS) and super GOSS. The new models are intended to estimate, right from the design phase, the magnetic flux density, permeability and the reluctance in the joints. The maximum differences between the Gaussian models of this study and finite element simulations are under 6%. The models of this study can be used to improve core designs with the aim of reducing core losses and magnetising current. A comparison of the total losses computed with the model of the study and measurements on a wound core distribution transformer showed differences of about 2.5%.
2017
This paper presents a finite element (FE) analysis of combinations of electrical steels in the lamination core steps of a real 6.3 MVA single-phase distribution transformer. The magnetic core of this transformer has a cruciform cross-section with lamination core steps. Two electrical steels are combined in the lamination core steps of transformer: a convectional grain oriented electrical steel (M-5) and laser-scribed electrical steel (23ZDKH90). 3-D FE simulations are performed to calculate the core losses (no-load losses) without and with combinations of electrical steels. B-H curves and iron loss curves of electrical steels are taken into account in the numerical simulations. The core loss calculated in FE simulation without combination of steels is compared with the core loss measured in no-load laboratory tests. Results obtained in this paper show that the combination of electrical steels in the lamination core steps can reduce 5% the core losses in single-phase distribution tra...
Proceedings of the IEEE International Autumn Meeting on Power, Electronics and Computing ROPEC 2017, Ixtapa, Mexico, November 8-10, 2017
This paper presents an electromagnetic finite element (FE) analysis of combinations of electrical steels in the lamination core steps of a real 6.3 MVA single-phase distribution transformer. The magnetic core of this transformer has a cruciform cross-section with lamination core steps. Two electrical steels are combined in the lamination core steps of transformer: a convectional grain oriented electrical steel (M-5) and laser-scribed electrical steel (23ZDKH90). 3-D FE simulations are performed to calculate the core losses (no-load losses) without and with combinations of electrical steels. B-H curves and iron loss curves of electrical steels are taken into account in the numerical simulations. The core loss calculated in FE simulation without combination of steels is compared with the core loss measured in no-load laboratory tests. Numerical results show that the combination of electrical steels in the lamination core steps can reduce 5% the core losses in single-phase distribution transformers with stacked magnetic cores. Finally, material costs are estimated for the steel combinations in the magnetic core of transformer.
Octagonal Wound Core for Distribution Transformers Validated by Electromagnetic Field Analysis
This paper analyzes a novel configuration of transformer core, called octagonal wound core (OWC), and shows the minimization of the excitation current and the reduction of the eddy-current losses. The OWC is compared with the conventional wound core (CWC) configuration. The comparison is based on two-dimensional and three-dimensional finite-element method (FEM) simulations, taking into account the nonlinear properties of the magnetic material of the core. The results show that the OWC reduces the excitation current and the eddy-current losses when compared with CWC. Moreover, several combinations of grades of the grain-oriented silicon steel (GOSS) were investigated so as to further reduce the eddy-current losses and the excitation current.
IEEE Transactions on Magnetics, 2010
This paper analyzes a novel configuration of transformer core, called octagonal wound core (OWC), and shows the minimization of the excitation current and the reduction of the eddy-current losses. The OWC is compared with the conventional wound core (CWC) configuration. The comparison is based on two-dimensional and three-dimensional finite-element method (FEM) simulations, taking into account the nonlinear properties of the magnetic material of the core. The results show that the OWC reduces the excitation current and the eddy-current losses when compared with CWC. Moreover, several combinations of grades of the grain-oriented silicon steel (GOSS) were investigated so as to further reduce the eddy-current losses and the excitation current.