Short Circuit Stress Calculation in Power Transformer Using Finite Element Method on High Voltage Winding Displaced Vertically (original) (raw)
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Alexandria Engineering Journal, 2016
The aim of this work was to work out the mechanical stresses within transformer resulting from the extreme short-circuit currents. The forces and stresses set up in transformer windings as the result of exterior or interior short-circuits or of switching operations, are measured in detail. A variety of arrangements of windings in large power transformers are described. Points at which mostly high mechanical stresses take place in concentric windings are discussed in detail. Analytical and FEM calculations for individual short circuit forces, axial and radial have been discussed. The result was then compared with actual measurements on a prototype 20 MVA 132/11.5 kV power transformer [15]. Various failure mechanisms due to these forces have been discussed. Design parameters are also discussed, whose values determine the maximum stresses which may occur in any part of the transformer. Effects of irregularity in various parts and various properties of materials have been studied and the usage of appropriate material for withstanding the dynamic effects of SC is discussed. Effect of workmanship errors on short circuit withstand capability has also elucidated. Finally, a complete model is developed.
IEEE Transactions on Power Delivery, 2017
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 conductors often used in power transformer windings. In literature, there barely exist calculations to the radial buckling withstand capability of CTCs. Therefore, a Finite Element Analysis (FEA) 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 the use with CTCs.
Analytical estimation of short circuit axial and radial forces on power transformers windings
IET Generation, Transmission & Distribution, 2014
In this study, an analytical method is proposed to calculate exerted axial and radial forces on the high and low voltage (LV) windings in core type power transformers. Hence, an analytical modelling approach is proposed to compute short circuit currents in the transient mode and steady state. The proposed model includes non-linear characteristics of the core materials, eddy currents effects, symmetrical and asymmetrical hysteresis loops of the used laminates. Then, exerted axial and radial forces on the high and LV windings are analytically computed in the transient mode and steady state. In order to certify obtained analytical results, the two-dimensional (2D) time stepping finite element method (TSFEM) is utilised to determine aforementioned forces. In this modelling approach, the geometrical, electrical and magnetic characteristics of the core type transformer under short circuit fault are taken into account. Furthermore, three-dimensional TSFEM is employed to verify the analytical and 2D TSFEMs results.
2020
Short circuit electromagnetic forces are considered as important factor from design point of view of transformer and should be taken care of while designing a transformer as it has very serious damaging effect to the transformer. Short circuit forces are more dominant in case of large power transformers.The work has been carried out on a power distribution transformer. The procedure for the analysis of power distribution transformer can be used to calculate the short circuit electromagnetic forces of large power transformer also. Therefore, a 630kVA, 11/.433kV power distribution transformer has been modelled for analysing the short circuit electromagnetic forces. Windings are modelled in twenty-three sections and short circuit force of each and every section of the winding is calculated using Finite Element Method of analysis. Electromagnetic forces are calculated for single helical and double helical windings of transformer.
Measurement of Short-Circuit Effects on Transformer Winding with SFRA Method and Impact Test
Metrology and Measurement Systems, 2016
The paper presents theoretical and experimental analyses of a possible effect of the short-circuit forces on the transformer winding. The first part of the paper is focused on creation and activity of the radial and axial forces during a short circuit. It shows dimensions, direction and − of course − the resulting mechanical stress. The presented equation shows basic dependencies of these mechanical forces created in the transformer winding. Finally, the paper presents experimental methods of diagnosing and analysing the effects of short-circuit forces on the transformer winding.
Power transformer under short-circuit fault conditions: A multiphysics approach
Transformers Magazine, 2020
Transformers' windings experience mechanical loads from electromagnetic forces due to the currents they carry. During normal operation, the resulting stresses and strains have minor influence, therefore they do not represent the significant risk to the devices' integrity. However, transformers can suffer from high sudden short-circuit currents that are several times higher than those during the normal operation. These short-circuit currents are a significant threat, not only from an electrical but also from the structural integrity point of view. In this paper, coupled electromagnetic and structural mechanics simulations are carried out to evaluate short-circuit fault risks in a comprehensive and accurate way.
Analyzing Short Circuit Forces in Transformer for Double Layer Helical LV Winding using FEM
International Journal of Performability Engineering
In medium and high capacity transformers where current rating is high and the number of turns is low, the low voltage (LV) winding is generally of the helical type. These helical windings have very large magnitudes of electromagnetic forces during a short circuit. This is due to the inherent asymmetry of helical structure. The objective of this work is to use the finite element method to compute the radial and axial components of short circuit forces and identify areas of high stresses in the windings. This can be used to find the likely reason of transformer failure during a short circuit. For this work, a 3-phase power distribution transformer of 11kV/433V, 630kVA rating is considered. The effect on short circuit forces of the tapping in the center of HV winding is also studied.
Dynamic behaviour of transformer winding under short-circuits
2008
The work presented in this thesis contributes to the understanding of the dynamic behaviour of large power transformer windings under short circuit forces. A simple yet accurate method of prediction of electromagnetic forces is developed and used as input to the dynamic mechanical model. In developing this model the mechanical properties of oil-impregnated pressboard have been investigated and measured in a specially designed rig which simulates the typical power transformer environment. Assumptions have been made regarding these properties to enable them to be meaningfully incorporated in a dynamic model of a transformer. Predictions made using the model have been compared with actual measurements on a transformer and a correlation within 20%-30% was achieved. The work demonstrated the importance of mechanical prestress to ensure that no serious nonlinearities will be encountered in the mechanical behaviour when short-circuit forces are present in a power transformer. It was also f...
Electromagnetic Forces in Power Transformers under short circuit conditions
Zenodo (CERN European Organization for Nuclear Research), 2022
Power transformers are among the most expensive and key apparatuses in an electric power system. It is important thus, that they are properly protected and well-maintained. Transformers experience different stresses while in operation. The effect of electromagnetic force on transformer windings is worsened by electrical, mechanical, and thermal issues. Damage from the increase in electromagnetic force includes winding displacement, bending, and tearing. Therefore, it is essential to predict electromagnetic force when designing transformers. This paper investigated the causes and process of damage to transformer windings due to electromagnetic forces when these windings are short-circuited and recommended mitigation measures for the safer and more reliable operation of power transformers under such conditions.