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Journal ArticleDOI

Analysis of Buckling Strength of Inner Windings in Transformers Under Radial Short-Circuit Forces

01 Feb 2014-IEEE Transactions on Power Delivery (IEEE)-Vol. 29, Iss: 1, pp 241-245
TL;DR: In this paper, the Ramberg-Osgood stress-strain relation has been used to calculate the critical buckling stress and compared with the resulting stress, and the analytically obtained result of the strain induced in the winding conductor during its winding process has been verified using the finite-element method.
Abstract: The buckling of conductors of inner windings in transformers is one of the major causes of their failures. It can occur when a large magnitude of radial short-circuit electromagnetic force acts on them. In this paper, initially, mechanical strains developed during winding processes and due to radial short-circuit forces have been determined. The two mechanical strains viz. the short-circuit induced strain and the winding process-induced strain are algebraically added to obtain their resulting strain. The stress corresponding to the resulting strain has been determined by using the Ramberg-Osgood stress-strain relation. The critical buckling stress has been calculated and compared with the resulting stress. The analytically obtained result of the strain induced in the winding conductor during its winding process has been verified using the finite-element method. A case study has been described in which the factor of safety against the buckling strength is determined.
Citations
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Journal ArticleDOI
TL;DR: In this paper, a finite-element analysis-based simulation model for CTCs is proposed and verified by the tests, and the final simulation model is based on a coupled analysis of magnetostatic force calculation and static structural deformation analysis.
Abstract: A test stand to evaluate the radial buckling strength of power transformer windings under the influence of electromagnetic forces is presented. The resulting conductor deformation can be measured in parallel to the sinusoidal test current. The proposed test results focus on the inception of forced buckling for continuously transposed conductors (CTCs), which are a special type of conductor often used in power transformer windings. In the literature, there barely exist calculations to the radial buckling withstand capability of CTCs. Therefore, a finite-element analysis-based simulation model for this kind of conductor is proposed and verified by the tests. For this verification, three different CTC types are used. The final simulation model is based on a coupled analysis of magnetostatic force calculation and static structural deformation analysis. It suitably reproduces the measurement results from the dynamic short-circuit tests. Furthermore, a standard formula describing radial buckling phenomena inside power transformers is adapted for use with CTCs.

41 citations


Cites background or methods from "Analysis of Buckling Strength of In..."

  • ...In the past, there have been many experiments and analytic as well as simulative investigations in order to master the short-circuit strength of power transformers [1]–[8]....

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  • ...In literature, the critical buckling stress is often calculated by the linear elastic approach [8] to...

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  • ...In [8] a buckling strength analysis for an epoxy bonded CTC winding is proposed....

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Journal ArticleDOI
Longnv Li1, Xiaoming Liu1, Gaojia Zhu1, Hai Chen1, Shengwei Gao1 
TL;DR: A comprehensive analysis of the characteristics of the split-winding transformer with stabilizing windings under different short-circuit faults reveals that the axial forces exerted on the winding in half-crossing short- Circuit faults are generally larger than those in full-crossed short-Circuit faults.
Abstract: Short-circuit faults are inevitable in split-winding transformers with stabilizing windings, and the resulting transient electromagnetic force may cause detrimental damages to the equipment. This paper focuses on a comprehensive analysis of the characteristics of the split-winding transformer with stabilizing windings under different short-circuit faults. In this regard, a FEM based on a field-circuit coupled approach is proposed. Also, a SFFZ10-88000-kVA split-winding transformer with stabilizing windings is used as a prototype to investigate its transient performances with both full-crossing and half-crossing conditions under different short-circuit faults. The symmetrical component method is presented to compute short-circuit currents to compare with the simulation ones, and a prototype test model is established to verify the correctness of the proposed method. The results reveal that the axial forces exerted on the winding in half-crossing short-circuit faults are generally larger than those in full-crossing short-circuit faults. Moreover, there is a considerable short-circuit force in the stabilizing winding in cases of a single-phase earthed fault and a two-phase earthed fault and there is no current in the stabilizing winding under other short-circuit fault cases. The numerical modeling approach dealt with in this paper is expected to be useful in the design of the split-winding transformer with stabilizing windings.

39 citations

Journal ArticleDOI
TL;DR: In this paper, the authors proposed an analytical method for determination of optimum distributive ratios resulting in minimization of short-circuit electromagnetic forces for asymmetrical multi-segment windings of an HTS transformer.
Abstract: High-temperature superconducting (HTS) transformers have a promising feature in reduction of total weight, total size, and the losses of large-scale distribution transformers. However, the lower leakage reactance of HTS transformers results in a higher short-circuit fault currents and electromagnetic forces. Therefore, optimization of short-circuit electromagnetic forces is one of the crucial aspects in the design of HTS transformers. In this paper, a novel analytical method is proposed for determination of optimum distributive ratios resulting in minimization of these forces for asymmetrical multi-segment windings of an HTS transformer. Employing these distributive ratios, radial and axial components of short-circuit electromagnetic forces in an HTS transformer are significantly reduced. Two- and three-dimensional (2D and 3D) finite element method (FEM) simulations are employed to verify the analytical method results.

16 citations

Journal ArticleDOI
TL;DR: In this paper, a method for analyzing the buckling strength of transformer windings based on electromagnetic thermal structure coupling method is presented, which takes into account the factors of plastic deformation and thermal effect.
Abstract: Winding buckling is a common and complex type of transformer failure. The commonly used method for calculating the buckling strength of transformer windings does not take into account the factors of plastic deformation and thermal effect. Therefore, in the stability analysis of the winding, the stress process of the default winding is ideal elastic. Even if some transformer windings meet the design standards, there is still the risk of instability in reality. A method for analyzing the buckling strength of transformer windings based on electromagnetic thermal structure coupling method is presented in this paper. Through a transformer example, the fault current, leakage magnetic field, and electromagnetic force of transformer are analyzed by field circuit coupling method. A model of the relationship between temperature and yield strength is established, and the temperature rise and ultimate instability load of transformer windings are analyzed by finite element method and experiment. The influence of plastic deformation and thermal effect on the ultimate instability load is considered. The results show that plastic deformation and temperature rise should not be ignored in the buckling strength analysis of transformer windings. The research results have certain reference value for transformer design.

15 citations


Cites background from "Analysis of Buckling Strength of In..."

  • ...There are few researches on the calculation of winding buckling strength [4], [5]....

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Journal ArticleDOI
TL;DR: In this article, a methodology based on computer simulations and aiming to estimate the lifespan of transformer windings after the occurrence of short circuits is presented, where the Von Mises and fatigue criteria are employed to determine the failure proximity of the windings.
Abstract: A methodology based on computer simulations and aiming to estimate the lifespan of transformer windings after the occurrence of short circuits is presented in this paper. The Von Mises and fatigue criteria are employed to determine the failure proximity of the windings. The obtained results contribute to the evaluation of the influence of electromechanical effects in transformer windings and to the determination of the number of short circuits that a transformer winding can support. The simulation results may also be employed in the design of transformers and failure diagnosis, to increase the security margin against mechanical failures.

15 citations


Cites background from "Analysis of Buckling Strength of In..."

  • ...On the other hand, the kinetic characteristics of windings, under short circuit conditions, have been widely analyzed numerically and the winding stability calculation has been the central issue in the safe operation of transformers [8]–[10]....

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References
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Book
01 Jan 1936

8,152 citations

Book
06 Sep 2012
TL;DR: Transformer Engineering: Design, Technology, and Diagnostics, Second Edition as discussed by the authors helps to design better transformers, apply advanced numerical field computations more effectively, and tackle operational and maintenance issues.
Abstract: Transformer Engineering: Design, Technology, and Diagnostics, Second Edition helps you design better transformers, apply advanced numerical field computations more effectively, and tackle operational and maintenance issues. Building on the bestselling Transformer Engineering: Design and Practice, this greatly expanded second edition also emphasizes diagnostic aspects and transformer-system interactions. What’s New in This Edition Three new chapters on electromagnetic fields in transformers, transformer-system interactions and modeling, and monitoring and diagnostics An extensively revised chapter on recent trends in transformer technology An extensively updated chapter on short-circuit strength, including failure mechanisms and safety factors A step-by-step procedure for designing a transformer Updates throughout, reflecting advances in the field A blend of theory and practice, this comprehensive book examines aspects of transformer engineering, from design to diagnostics. It thoroughly explains electromagnetic fields and the finite element method to help you solve practical problems related to transformers. Coverage includes important design challenges, such as eddy and stray loss evaluation and control, transient response, short-circuit withstand and strength, and insulation design. The authors also give pointers for further research. Students and engineers starting their careers will appreciate the sample design of a typical power transformer. Presenting in-depth explanations, modern computational techniques, and emerging trends, this is a valuable reference for those working in the transformer industry, as well as for students and researchers. It offers guidance in optimizing and enhancing transformer design, manufacturing, and condition monitoring to meet the challenges of a highly competitive market.

142 citations


"Analysis of Buckling Strength of In..." refers background in this paper

  • ...The higher its value, the higher will be the value of the critical buckling stress [2], [12]....

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  • ...The effect of radial forces on an outer winding is to produce tensile hoop stresses in its conductors, and they produce compressive hoop stresses in an inner winding which must be adequately supported to avoid its failure [1], [2]....

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Book
01 Sep 1966

65 citations


"Analysis of Buckling Strength of In..." refers background in this paper

  • ...The effect of radial forces on an outer winding is to produce tensile hoop stresses in its conductors, and they produce compressive hoop stresses in an inner winding which must be adequately supported to avoid its failure [1], [2]....

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Journal ArticleDOI
K. Kurita, T. Kuriyama, K. Hiraishi, S. Kusumoto1, Shigeru Shida1, Yasara Hori1 
TL;DR: In this paper, the authors have developed a new short-circuit testing method and have proved the method to be an effective means of finding the shortcircuit strength of transformer windings.
Abstract: For the past few years, the authors have studied the short-circuit strength of large transformer windings. In the course of the study, they have developed a new short-circuit testing method and have proved the method to be an effective means of finding the short-circuit strength of transformer windings. The new testing method and test results will be described in the following, together with a few observations.

34 citations


"Analysis of Buckling Strength of In..." refers background in this paper

  • ...Inner windings generally fail due to a buckling phenomenon [3]–[5]....

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