Transformer Joints FE Analysis Using Pseudo-Source Technique

Proceedings of the 23rd International Conference on Electrical Machines ICEM 2018, Alexandroupoli, Greece, September 3-6, 2018

This paper describes a finite–element (FE) based application for the numerical evaluation of core–losses in distribution transformer. The specific application is centered around a method that permits the generation of software applications for a variety of user/customer defined problems and makes use of the FE method in order to solve them. A variety of problems are considered such as electromagnetic or thermal, steady state or transient, linear or non–linear, and two– dimensional (2–D) or three–dimensional (3–D). The present manuscript focuses on one such application and more specifically on the problem of core–losses evaluation in oil– immersed, wound core, distribution transformers, both single– phase and three–phase. Finally, the core–losses of a single–phase wound core transformer are computed using the " CORELOSS " application and they are compared with results obtained with a commercial FE package.

IEEE Transactions on Magnetics, 2000

International Journal of Power and Energy Systems (ACTA Press), 2003

This work analyzes the behaviour of wound-cores losses in distribution transformers, as a function of the design parameters of the transformer joint configuration. The configuration used in this paper is called step-lap joint. This analysis is carried out experimentally as well as by using the finite element method. In this research, the effect of the following factors is considered: (a) overlap length and (b) number of laminations per step or group. The design aspects of the wound core are also discussed.

Master of Engineering Thesis GTU India, 2013

Transformers are most essential and consequential elements in electricity transmission and distribution. Therefore, in order to have a transformer working at optimum level, many researches and tests have been being performed. The goal of these tests and researches is reducing the amount of losses and extends lifetime of a transformer. During the conversion of the electricity in a transformer, some losses occur. These losses occur at windings and core of the transformer and they turn into heat. Transformers are widely used in almost all industrial application and is must for any basic industrial setup. As every machine, when running under normal condition is subjected to different kind of faults, the solution of which has to be carried out in advance to achieve best possible efficiency before actual use of the transformer. In the initial step, we go through the numerous papers which has worked on different parameters of transformer using FEM analysis. And the results of the same will be used in determining modelling of a transformer in the software using Finite Element approach. This method helps to develop accurate models of the machine under both healthy and faulty conditions. It also accurately calculates magnetic fields and related transformer design parameters for different types of transformers with completed geometry, which increases possibilities of improving the design during the planning stage (Before actual use of transformer). Using this method, analysis of Internal Insulation Design Improvements, Accurate Prediction and Minimization of No Load Loss, Internal Stresses at high frequency and faults like leakage reactance, internal winding stress etc. will be carried out. The analysis with the fault condition listed above will be simulated in FEM based software and the result will be compared with that of the transformer under healthy condition, which helps a great in knowing the worst possible condition under which transformer can be used. The design of the transformer carried out by the above method will be helpful to the industry in the sense that maximum possible efficiency and accurate calculation of magnetic field and stresses on windings can be achieved under worst possible conditions.

International Transactions on Electrical Energy Systems, 2018

Reducing the losses of 3-phase transformers is still considered a significant target by many transformer designers and manufacturers. Core joint design is one of the factors related to the losses. In previous studies, core losses and flux density distribution motivated researchers to design appropriate T-joints. However, the variation of load and thermal profiles are the most important factors related to the losses in transformers. This study proposed a new T-joint configuration for the core of the 3-phase transformer. The proposed model was built after considering the variation of load and thermal profiles. Results were compared with those of conventional T-joint designs, such as butt-lap and 45°mitered designs, that are currently used. The no-load losses of the proposed model were reduced by more than 6.8% and 10% compared with those of the butt-lap and mitered T-joint designs, respectively. Furthermore, the total losses, the hot spot temperature of the core, and the oil temperature decreased significantly. The proposed model contributes to the literature on new T-joint designs for improving transformer performance. KEYWORDS core loss, finite element, flux density, joint design, power transformer The 3-phase distribution transformer is a significant component of an electrical distribution grid. The losses of transformers consist of no-load and load losses. Losses incessantly lead to loss of energy in transformers, which are connected to the network. Thus, more energy is lost and undesirable factors appear, which affect transformer performance. The power transformer is an important component of a power system, and its efficiency reaches 98%. 1 Core loss accounts for approximately 70% of the total transformer losses, whereas the operating (or energy) efficiency is 93.38%. Thus, a worldwide concern on core losses exists and should be reduced. In electrical transformers, iron losses are important for thermal designs and electromagnetic analyses. In the past few contracts, we have witnessed rapid changes in the field of transformer design and manufacturing. As a general rule, increasing flux density by 1% increases losses by approximately 2%. The efficiency of a transformer core is largely dependent on the design of the joints, such as corner and T-joints. At the T-joint area of the core of a 3-phase transformer, the direction of magnetization in laminations may change during the magnetizing cycle, resulting in the increase in rotational flux. Therefore, designing the optimum core

IEEE Transactions on Magnetics, 1980

The author is indebted to C. W. Steele for many helpful discussions. [7] D. A. Lindholm, "Secondary gap effect in narrow and wide track reproduce heads," IEEE

COMPEL, vol. 31, no. 2, pp. 682-691, 2012

Purpose – This paper aims to present an accurate representation of laminated wound cores with a low computational cost using 2D and 3D finite element (FE) method. Design/methodology/approach – The authors developed an anisotropy model in order to model laminated wound cores. The anisotropy model was integrated to the 2D and 3D FE method. A comparison between 2D and 3D FE techniques was carried out. FE techniques were validated by experimental analysis. Findings – In the case of no-load operation of wound core transformers both 2D and 3D FE techniques yield the same results. Computed and experimental local flux density distribution and no-load loss agree within 2 per cent to 6 per cent. Originality/value – The originality of the paper consists in the development of an anisotropy model specifically formulated for laminated wound cores, and in the effective representation of electrical steels using a composite single-valued function. By using the aforementioned techniques, the FE computational cost is minimised and the 3D FE analysis of wound cores is rendered practical.

The paper presents an accurate and cost effective three-dimensional finite element model for the analysis and design of wound core, shell type, power transformers, focusing on the short-circuit impedance evaluation. The model efficiency lies on the detailed representation of the transformer geometry along with the adoption of a particular reduced scalar potential formulation enabling three-dimensional magnetostatic problem solution without prior source field calculation. Its accuracy is validated through local field measurements and through comparison of the calculated short-circuit impedance value with the measured one for several commercial wound core, shell type transformers. In such transformers, involving extensive winding parts out of the core window, the detailed representation of the transformer geometry, including the winding cooling ducts, provides accurate results for low densities of the three-dimensional finite element mesh, resulting to reduction of the required calculation time. The model is used in the development of a computational tool, which enables the automated and accurate transformer characteristics prediction, adopted to the manufacturing process. This tool has also been applied in the impedance calculation for different winding connections of dual voltage transformers, thus providing the information needed for the achievement of an accurate design and the enhancement of the manufacturer's ability to reduce design margins. The methodology presented in this paper has been incorporated in the design process of a transformer manufacturing industry.

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.

labplan.ufsc.br

This work deals with the representation in two dimensions of three-phase and three-limb transformers using FEMM, where the associated modeling limitations are overcome by the appropriate adjustments proposed in this work regarding the transformer dimensions and the obtained simulated results. The intrinsic small air gaps due to the core steel sheet junctions, which are normally neglected, are included in the modeling, and a method for the calculation of their reluctance is presented, based on the transformer magnetic circuit and on the maximum value of the magnetization current waveform in each winding, obtained through the no-load test. The magnetic flux distribution in the limb and yoke segments of the core is compared to design values and the effects of the inherent air gaps in the magnetization current are analyzed. In order to improve the model, a more accurate representation of the windings is also presented. Finally, the transformer leakage reactance is calculated through simulations and compared with the value obtained from the experimental method.