Short-circuit Forces Research Articles

Research on Magnetic Characteristics and Short-Circuit Force of 3D Wound Core Transformer

The problem of eddy current loss in power transformers directly affects the technical economy of the transformer, which is a problem that cannot be ignored in the design and calculation of power transformers. Studying how to reduce the eddy current losses caused by leakage magnetic fields is a difficult point in transformer design. The load loss of low-voltage foil copper windings in a 10 kV/400 kVA 3D wound core transformer is calculated, and the three-dimensional finite element models of the transformer are established by Using Magnet software and COMSOL Multiphysics software, and the calculation results are compared. At the same time, the short-circuit force of foil windings is shown in the simulation. The results show that the three-dimensional finite element models are correct.

Numerical Investigations for Vibration and Deformation of Power Transformer Windings under Short-Circuit Condition

The analysis of the dynamic process of winding destabilization under sudden short-circuit conditions is of great importance to accurately assess the short-circuit resistance of power transformers. Based on magneto-solid coupling, an axisymmetric model of the transformer and a 3D multilayer model of the transformer considering the support components are established, respectively, and the short-circuit electromagnetic force (EF) is simulated by using the finite element method. It is concluded that the middle layer of the winding is subjected to the larger radial EF, while the axial EF has a greater effect on the layers at both ends. Moreover, the impression of the preload force, aging temperatures, and the area share of spacers on the vibration and deformation of windings are studied under short-circuit conditions. The overall distribution of plastic strain and residual stress in the winding is symmetrical, and the maximum values occur in the lower region of the middle of the winding. Finally, considering the material properties of disks and insulating components, the cumulative effect of plastic deformation under multiple successive short-circuit shocks is calculated. Compared with the traditional axisymmetric model of transformer, the three-dimensional multilayer model of the transformer established in this paper is more suitable for the actual winding structure and the obtained results are more accurate.

Calculation and Analysis of Short Circuit Strength of Three-Winding Transformer

The transformer is the most important in the entire power system and is also one of the most expensive devices. The operating condition of the transformer affects itself and at the same time concerns the stability and safety of the whole power system. This paper deals with leakage field, short-circuit electromotive force, and other issues in the transformer. The basic data of the SFSZ-40000/110 power transformer is calculated as an example, and then the leakage field of winding and short-circuit electromotive force is calculated and analyzed.

Analysis of Transformer Winding Deformation and Its Locations With High Probability of Occurrence

Power transformer, as a crucial equipment for power transmission, frequently suffers winding deformation defects, owing to the impact of huge external short-circuit current in actual operation. To resist the rapid deterioration of the defects, online monitoring for winding states is imperative, depending on a thorough understanding of the deformation defects. Unfortunately, there are not much related research on the deformation form and location, as two key objects online diagnosed. In this paper, we concentrate on the analysis of winding deformation and investigation of its high-probability location to deeply understand the winding deformation. For the form of the deformation, a three-dimensional finite element model of the transformer is established to obtain the form and extent of the short-circuit impact force, and a buckling model of the low-voltage winding is designed to analyze the mechanism and form of winding deformation under the impact of huge force induced by short-circuit current. For the location of the deformation, the three-dimensional simulation models are established to analyze the force characteristics of different winding structures in three locations (the conductor transposition area, the area with imbalanced amp-turns and the area with uneven circumferential distribution of force). Then we clarify the possibility of winding deformation in these areas, defined as high-probability locations. Finally, the analyzed results are found to be highly consistent with the actual winding deformation, demonstrating the correctness of the research methods and conclusions. Next stage, the results will provide effective theoretical support for online diagnosis of winding deformation and optimal design of winding structure.

Electromagnetic Field Analysis and Optimization Method of High-Temperature Superconducting Transformer under the Influence of Abnormal Voltage

High-temperature superconducting transformers are an important research topic of superconducting technology in power applications, and electromagnetic field analysis and optimization are the basis for the design and application of high-temperature superconducting transformers. The electromagnetic field analysis of high-temperature superconducting transformers should consider the superconducting properties of the materials, that is, the properties of critical current and magnetic field. This paper aims to study the electromagnetic field analysis and optimization method of high-temperature superconducting transformer under the influence of abnormal voltage. Due to the energy loss of high-temperature superconducting transformers, in order to study the economy and reliability of high-temperature superconducting transformers, in this paper, the core loss, winding AC loss, and coil power consumption of high-temperature superconducting transformers are analyzed under normal operation and short-circuit fault conditions, respectively. The power and stress on the windings are analyzed. In order to take into account the current-carrying capacity, short-circuit loss, and short-circuit electromotive force of superconducting windings in normal operation, a concentrically placed double-cake coil structure is selected in this paper, and according to different optimization objectives, a global optimization method is used to evaluate the structure of the coil. The structural parameters of the high-temperature superconducting transformer are optimized, including the structural parameters of the magnetic conducting ring. It is found that that abnormal voltage will affect the electromagnetic field of high-temperature superconducting transformers, including winding circulating current, leakage magnetic field, and current distribution.

Coupled magneto-mechanical finite element analysis of a power transformer in short circuit conditions

External short circuit is one of the most demanding load conditions a transformer can be subjected to. Short circuit withstand capability of power transformers is therefore quintessentially important in order to ensure the proper functioning of a power transformer during its lifetime. Accurate calculation of the forces and stresses a transformer is subjected to during a short circuit is a prerequisite for better, optimized design of the active part. Main focus of this paper is the investigation into dynamic electromagnetic and mechanical behaviour of a transformer winding subject to an external short circuit. For purposes of this simulation, a single-phase 100 MVA autotransformer active part was modelled using ANSYS and NACS software. Particular areas of the winding were modelled to a greater degree of detail in order to observe the effects of Lorentz forces during a short circuit on individual conductors. A transient coupled magneto-mechanical simulation of the transformer under short circuit conditions was carried out. When subject to dynamic short circuit forces, the winding discs exhibited a profoundly resonant behaviour indicating a strong relationship between the natural frequency of the winding and the resulting stresses and displacements incurred during a short circuit. It has been shown that the position of the yoke changes the orientation and the distribution of the magnetic field vectors at the top and the bottom of the winding, causing a non-uniform distribution of forces along the top discs of the winding. This non-uniform distribution of forces along the circular shape of the winding conductor caused high stresses at the positions within the winding which were previously considered to be under lower stress when calculated using 3D static FEM and analytical methods.

Coupled Magnetic-Structural Modeling of Power Transformer for Axial Vibration Analysis Under Short-Circuit Condition

When an external short circuit occurs, the axial electromagnetic force increases dozens of times. Under the effect of the axial short-circuit electromagnetic force, the transformer windings vibrate violently. The spatial distribution of the disks is constantly changing during vibration, which can change the temporal and spatial distributions of the leakage magnetic field and the axial electromagnetic force. This process is called the strong coupling phenomenon of the structural field and the leakage magnetic field. In this article, a strong coupled magnetic-structural model is proposed by using the analysis method. The strong coupling equations, where the independent variables are the axial position of the disks, are obtained. The vibration process with strong coupling phenomenon considered can be obtained. The accuracy of the strong coupling model is verified by the iterative method. By comparing the results calculated by the strong coupling model with those calculated by the weak coupling model, the influence of the strong coupling phenomenon <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</b> the vibration process is obtained. Due to the influence of the strong coupling phenomenon, the winding vibration intensity increases and the maximum displacement of the disks can be doubled, which implied that the strong coupling phenomenon cannot be ignored when investigating the short-circuit strength of power transformers.

Research on Single-phase Power Supply in Short-circuit Test of Transformer on Magnetic-force Coupling Field

The short-circuit test is a test of the comprehensive technical ability of transformer manufacturing. The three-phase power supply is usually used for short-circuit test of transformer. To investigate the feasibility of using a single-phase power supply in the short-circuit test of transformer, in this paper, we modeled a 200 kVA power transformer in three dimensions, using the finite element method to calculate the short-circuit current and short-circuit electromagnetic force of the windings under different excitation modes when the three-phase short-circuit occurs in the low-voltage windings. Analyze and compare the short-circuit current and short-circuit electromagnetic force distribution characteristics of windings under different working conditions. The results show that when the three-phase short-circuit condition occurred in the low-voltage windings, regardless of the three-phase excitation or single-phase excitation exerted on the high-voltage windings, the short-circuit current and the short-circuit electromagnetic force of the voltage zero-crossing closing phase is basically the same. This proves that a single-phase power supply can be used instead of a three-phase power supply for short-circuit tests. the analysis result has certain reference significance for improving the short-circuit test of transformer.

Research on Electromagnetic Force of Transformer in Different Short-circuit Modes

When a short-circuit fault occurs on a power transformer, the windings of the transformer under the combined action of the short-circuit current and the leakage magnetic field, which is easy to deform the winding or damage the insulation of the transformer. Therefore, it is necessary to research on the force of the transformer under short-circuit situation, analyze and calculate the size and distribution characteristics of the electromagnetic force in different short-circuit modes. Based on the structural parameters of a transformer with a rated capacity of 200kVA, a three-dimensional model of a three-phase transformer is established by finite element simulation software. The axial and radial electromagnetic forces of windings in different short-circuit modes are analyzed by this model, comparing and analyzing the experimental results. In the simulation model, It can be known that the electromagnetic force of voltage zero-crossing closing phase when three-phase short-circuit occurs on low-voltage winding is basically the same as that of short-circuit phase electromagnetic force when single-phase short-circuit occurs. The analysis results have a certain reference value for improving transformer short-circuit withstand ability.

Research on Measurement of Transformer Short-Circuit Force Using Piezoelectric Thin Film Polyvinylidene Fluoride Sensor

This paper presents a newly designed piezoelectric thin film polyvinylidene fluoride (PVDF) sensor that is able to measure short-circuit force directly in a short-circuit test. The sensor, with its advantages of high sensitivity, thin shape and shock-resistant, could measure the axial and radial short-circuit force which is usually difficult to measure due to large voltage and small gap between transformer windings during a short-circuit test, and thus provides a good way to study the ability of transformers to withstand short circuit, in which case many transformer accidents are caused. In the first part the working principle of PVDF sensor and the design of PVDF sensor in transformers are described. The following part introduces the calculation and simulation of the sensor and the short-circuit force. A real short-circuit test with PVDF sensor is then recorded and analyzed in the following part. And it is finally concluded that the piezoelectric thin film PVDF sensor is proved to have high accuracy in the measurement of the short-circuit force of transformer.

HTS transformers leakage flux and short circuit force mitigation through optimal design of auxiliary windings

Mitigation and control of leakage fluxes and short circuit forces needs much more attention, for a high-temperature superconducting (HTS) transformer, than for a conventional one. Different methods such as the application of auxiliary windings, multi-segment winding, and flux diverter have been presented in the literatures for leakage magnetic field reduction in HTS transformers. In this paper, for the first time, optimal design of auxiliary windings has been performed for a 132/13.8 kV, 50 MVA three phase core type HTS transformer. Genetic algorithm (GA) has been used for the optimization process. Induced current in auxiliary windings which is inversely proportional to the leakage fluxes and short circuit forces has been considered as the objective function. An analytical method has been proposed in this paper which formulates the objective function in terms of the self and mutual inductances of the main and auxiliary windings. Consequently, the optimal parameters of the auxiliary windings have been determined. It is shown that utilizing the optimized auxiliary windings design, the leakage fluxes, the radial and the axial components of the short circuit forces are reduced significantly. Two-dimensional electromagnetic field simulations using finite element method (FEM) by application of COMSOL multiphysics software have verified the theoretical formulations.

Assessment of the use of FEM for computation of Electromagnetic Forces, Losses and Design of Transformers

This paper reviews the published work on power transformers for assessment of the electrical, magnetic losses, and electromagnetic forces produced during normal and short circuit conditions. The different methods used are analytical method, integral equation method, boundary element method, and finite element method (FEM). The copper losses and eddy currents within the copper conductors/windings need to be assessed to estimate the heat generate and compute the efficiency. The knowledge of the eddy current losses in the core and stray losses in each component of the transformer can help in the design improvement. Earlier 2D FEM and now 3D FEM has been used to evaluate the electromagnetic flux under normal conditions, the effect of the in-rush phenomenon, assessment of mechanical strength of windings, insulation, computation of short circuit forces and need of the mechanical support components during fault conditions. This paper gives an overview of the work done on the computation of electromagnetic forces, losses, and design of transformers using FEM to assess the scope for further work.

Simulation modeling study on short circuit ability of distribution transformer

Under short circuit condition, the oil immersed distribution transformer will endure combined electro-thermal stress, eventually lead to the mechanical damage of the inner winding of distribution transformer, therefore it is necessary to study the short circuit ability of the oil immersed distribution transformer. In this paper, the typical current waveform of the distribution transformer under the short-circuit condition is analyzed theoretically. The short circuit fault simulation model of distribution transformer is built on the MATLAB/Simulink simulation platform, the short circuit waveform of the single phase, double phase and three phase short circuit is obtained. Further on the ANSYS simulation platform, three dimensional solid modeling of the three-phase five column transformer is carried out, the harmonic and transient field are applied to analyze the magnetic field distribution of the key components in distribution transformer under the short circuit condition, the internal cause of large short-circuit force in the winding of the distribution transformer under the short circuit condition is analyzed to certain extent. The results of the modeling and simulation show that the three phase short circuit current is larger than the single-phase and bi-phase short circuit current. Its value is 1.45 times the normal running current, which is the gradual damping asymmetrical short-circuit current. Magnetic induction intensity is in-homogeneous in the circumferential direction of the core column, and the degree of in-homogeneity varies along height. The magnetic density distribution under the short circuit condition is more than 6 times as much as the the normal condition. From the point of view of simulation modeling, short circuit ability of the oil immersed distribution transformer is analyzed, distribution characteristics of short circuit current and magnetic field of oil immersed distribution transformer under short circuit condition have been obtained, the theoretical reference value of the state characteristics and protection measures of oil immersed distribution transformer under the overload condition can be provided.

Research on simulation calculation on short-circuit electrodynamics force of power transformer winding

The safety and reliable operation of power grid is directly related to the ability of power transformer to withstand short-circuit, therefore, it is a problem to be solved to improve the ability of large power transformer windings to withstand short-circuit. Taking a three-phase five-limb power transformer as an example, the transient electromagnetic field, short-circuit electrodynamics force of windings and mechanical strength of coils are analyzed in depth. Firstly, the three-dimensional finite element model of the prototype is established, and the magnetic flux density distribution of the three-dimensional transient electromagnetic field of transformer under short-circuit operation and the axial and radial static force magnitude of the winding are calculated by using the field-circuit coupling method, and the distribution law can be obtained. At the same time, the mechanical strength of power transformer winding in its height direction is discussed, and the modal vibration mathematical model of transformer low-voltage winding in Z-axis direction is established. The displacement change and resonance frequency of the winding wire cake in the axial direction caused by short-circuit are calculated, and the short-circuit electrodynamics force of the winding is also checked. The research in this paper provides a theoretical basis for strengthening the design of short-circuit withstanding capacity of windings, and has a certain theoretical and engineering application value.

Optimal Design of Flux Diverter Using Genetic Algorithm for Axial Short Circuit Force Reduction in HTS Transformers

The appealing advantages of high-temperature superconducting (HTS) power transformers over conventional ones have attracted transformer manufacturing companies, power companies, research institutes, and universities worldwide to conduct research and development in this field. Unfortunately, HTS transformers are more vulnerable to mechanical stresses than conventional transformers. The results of the interaction between current carrying windings and leakage magnetic fluxes are the electromagnetic forces, which act on transformer windings. Under short circuit events, these forces are remarkable, and, therefore, catastrophic failure of transformer may arise. Flux-diverter applications have been reported in earlier literatures for increasing critical current or decreasing ac losses in HTS transformers. In this paper, a genetic algorithm based method is employed for the optimal design of flux diverter to minimize the axial short circuit force, in design stage of a sample 132/13.8 kV, 50 MVA three-phase core type HTS transformer. In this paper, the optimal dimensions, placement, and permeability of a flux diverter have been determined. It has been shown that utilizing this optimized flux diverter, the axial short circuit forces have been reduced significantly. Electromagnetic modeling and simulations, by the application of finite element method, have been employed for the verification of the analytical method results. A high degree of consistency has been observed between the analytical results and the simulation results.

전기기기] 전력용 변압기 권선의 탭 조건에 따른 단락 전자력 계산에 관한 연구

This paper deals with short-circuit electromagnetic force of power transformer depending on tap condition. In order to reduce the analysis time, we used a 2-D axi-symmetric model. Firstly, in order to prove the 2-D axi-symmetric model, we calculated percent impedance and maximum value of leakage magnetic flux density by using analytical method and finite element method. Secondly, short-circuit currents are calculated by using a short-circuit equation. Finally, short-circuit electromagnetic forces produced by short-circuit currents are computed by finite element method. And the results has compared depending on tap condition. The results are expected to be useful in structure design of power transformer.

Multi-segment Winding Application for Axial Short Circuit Force Reduction Under Tap Changer Operation in HTS Transformers

High-temperature superconducting (HTS) transformers have remarkable appealing advantages over conventional ones. But higher brittleness of HTS windings with respect to copper windings makes HTS transformers more vulnerable in short circuit and inrush current situations. During tap changer operation, appreciable asymmetry and non-uniform distribution of ampere-turn along the windings causes high axial component of short circuit forces and makes the situation more severe. In this paper, multi-segment winding method is employed for reduction of axial short circuit forces. An analytical method is presented for calculation of axial component of short circuit forces under tap changer operation. Analytical method shows that with utilizing HLHLHLH asymmetrical multi-segment windings, during tap changer operation, the axial component of short circuit forces reduces significantly. The results of the analytical method are compared with the results of finite element method (FEM) model simulations, and the consistency is demonstrated.

Research of Short-Circuit Performance of a Split-Winding Transformer With Stabilizing Windings

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.

HTS Transformer Windings Design Using Distributive Ratios for Minimization of Short Circuit Forces

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.

Testing and Analysis of Dynamic Response of a High-Voltage Substation Structure to Short-Circuit Current Forces

In substations, buswork, insulators, and supporting structures are subjected to electromagnetic forces caused by short circuits. The current industry design standard of practice is to apply the maximum instantaneous short-circuit force to the structure and perform simple static structural analysis to calculate supporting structure member. However, it is well known that this may be overly conservative since the applied forces and the response of the structure are dynamic in nature. To quantify the dynamic effects, full-scale short-circuit testing was performed on a typical 138 kV disconnect switch stand. The switch stand was instrumented with fiber optic strain gages and subjected to a variety of fault conditions. Extensive dynamic finite element analyses were performed on the subject structure, which were validated with the test data. The results confirm the reduced dynamic response of the structure. With further analyses, it is anticipated that a generalized quasi-static design methodology that considers dynamic response can be developed to replace the present short-circuit design approach.