Quasi-3D Finite Element Modeling of a Power Transformer (original) (raw)
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Reduction of Stray Losses in Flange–Bolt Regions of Large Power Transformer Tanks
IEEE Transactions on Industrial Electronics, 2014
In large power transformers, the presence of stray currents in the structural elements near the high current bushings can be considerable, and this leads to hot spots. This work presents a practical analysis of overheating in the bolts that join the tank and the cover, which are near the high current bushings of the transformer. Overheating results are analyzed and discussed for the case of a 420-MVA transformer. The hot spots in the flange–bolt regions are discovered by thermal maps that are obtained during power transformer operation as a part of a preventive maintenance program. In this paper, we use copper links to ensure the connection of both the cover and tank body, significantly reducing the overheating of the flange–bolt region. The copper link solution has been validated by measurements.We have used calibrated measurement instruments in all the experiments. Moreover, a 3-D finite-element analysis of the geometry of interest has been used to verify the copper link solution.
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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.
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Temperature Reduction in the Clamping Bolt Zone of Shunt Reactors: Design Enhancements
IEEE Transaction on Power Delivery, 2014
This paper presents design improvements to lower the temperature in the clamping bolt (CB), in a single-phase extrahigh- voltage (EHV) shunt reactor. Laboratory temperature measurements, under overload and nominal load conditions, were performed in the middle of the two top main air gaps inside one of the slots drilled in the CB using commercial fiber-optic temperature sensors. 3-D finite-element (FE) simulations were performed to calculate fringing losses in the CB. Subsequently, the fringing losses were employed as a heat source for static-steady thermal analysis using 3-D FE simulations. Convective heat-transfer coefficients were selected with a methodology that leads to a close match between measured and simulated temperatures. Two practical design enhancements to diminish temperatures in the CB are analyzed using measured and simulated data. These alternatives improve design and reduce potential failures and, hence, increase the EHV shunt reactor lifetime.
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A Bibliographic Analysis of Transformer Literature 1990-2000
This paper presents an analysis of the bibliography on transformers covering the period from 1990 to 2000. It contains all the transformer subjects: a) Transformer design, b) Transformer protection, c) Transformer connections, d) Transformer diagnostics, e) Transformer failures, f) Transient analysis of transformers (overvoltages, overcurrents), g) Modeling and analysis of transformer using FEM (thermal modeling, losses modeling, insulation modeling, windings mod-eling). Several international journals were investigated including the following: Systems, and IET Generation Transmission & Distribution. Due to the high number of publication in journals, we are not considering publications of conferences and symposia. A total of 700 publications are analyzed in this paper. The research presented in this paper is important because it contains and analyzes the best research papers on transformers coming from many countries all over the world and published in top rated scientific electrical engineering journals.
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Asymmetry During Load-Loss Measurement of Three-Phase Three-Limb Transformers
IEEE Transactions on Power Delivery, 2007
When the load-loss measurement test is conducted on three-phase transformers, an appreciable asymmetry is observed among the power readings of the three phases. This asymmetry is the result of two causes, viz. asymmetrical disposition of phases in space with respect to each other and unequal stray losses produced by phases. The disposition of phases leads to asymmetrical mutual impedances between phases and this is the principal contributor to the phenomenon. Another factor that may have an important contribution to the phenomenon is the deviation of the phase angle difference between the voltages of the three phase source (used during the test) from 120 . The causes are analyzed using a detailed three-dimensional (3-D) finite-element (FE) simulation of a 31.5 MVA, 132/33 kV transformer. In addition, a six-port network impedance model is deduced from open-circuit 3-D FE simulations. The impedance model is able to reproduce any condition of the transformer (e.g., open-circuit, short-circuit or on-load conditions) since it captures all the transformer electromagnetic phenomena. The six-port network results are discussed in order to elaborately clarify the intriguing problem of asymmetrical load-loss distribution, which is important for both transformer manufacturers and users. The results are further explained through sequence components of currents.
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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.
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2D Extraction of Open-Circuit Impedances of Three-Phase Transformers
This work is concerned with the study of the asymmetrical phenomenon observed in three-phase transformers during the standard short-circuit test. The purpose of our work is to see if the asymmetric measurements can be predicted with the use of 2D finite-element models. To this end, we ...
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2D finite-element determination of tank wall losses in pad-mounted transformers
Electric Power Systems Research, 2004
This paper presents a two-dimensional (2D) finite-element (FE) analysis of losses generated in the tank wall surrounding the high-current bushings of pad-mounted transformers. Although the problem is truly three-dimensional (3D), it is shown that a 2D approach gives results that closely agree with 3D simulations and experimental results. Thus, it is possible to avoid the very demanding computational resources required for 3D modeling or the cost of experiments. Nine cases are analyzed to study the impact of inserting small plates of different geometry (located near the high-current terminals) on the reduction of tank losses. Significant reductions in stray losses on the tank wall are obtained with low-cost plate inserts. 2D and 3D time-harmonic FE models are used to determine the losses in the tank wall. Two load loss tests were carried out on experimental transformers to validate the simulations.
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Core loss and excitation current model for wound core distribution transformers
This paper proposes a model for the computation of core losses and excitation current, in a lamination by lamination method, for wound core distribution transformers. The model was developed based on the finite-element method (FEM). The results obtained by applying the proposed model were compared with the FEM results and with the measurements of the no-load test. The no-load losses obtained by the proposed model present a difference of 4% with respect to measured values, while they are almost the same with respect to FEM. The proposed model contributes in the research of new techniques that improve transformer design.
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