Transformer Core Research Articles

Broadband Modelling of Power Transformers for Sweep Frequency Impedance Studies on Winding Short-Circuit Faults

To study sweep frequency impedance (SFI) features of short-circuit (SC) faults easily, this paper proposes a broadband electric circuit model of a transformer winding and solves its three key problems. The first problem is the calculation of lumped-circuit parameters considering frequency-dependent complex anisotropic permeabilities (FDCAPs), which are caused by the physical characteristics, such as skin, proximity, and geometrical effects and anisotropic properties, of the transformer core and winding materials. The other issue is the establishment of the electric circuit model based on the SFI measurement connection mode, the transformer winding parameters, and a double-ladder network (DLN). Another issue is the construction of the state-space model of the electric circuit toward different SFI values to obtain all network branch voltages and currents. The accuracy of the proposed model is assessed by comparing its SFI signatures with those of the simulation model, without considering FDCAPs under healthy winding, and the corresponding physical transformer model during healthy winding and SC faults. It is observed that the SFI results of the proposed model are closer to the experimental measurements, and the model can be effectively used to study the SFI features of SC faults. Moreover, the impacts of different types of SC faults on the SFI data are concluded in this paper.

Modeling magnetostriction of grain-oriented sheet steels based on magnetization process and domain motion

Grain-oriented (GO) sheet steels are preferred for magnetic cores in large power transformers because of their low core loss and high permeability. However, GO sheet steels exhibit more complex magnetostriction than non-oriented (NO) materials, causing undesirable vibrations and acoustic noises in the transformer core, especially under certain operating conditions, such as DC bias and magnetic saturation. This paper proposes a magnetostriction model of GO sheet steels based on an improved understanding of the magnetization process and domain motion. Incorporating the positive and negative magnetostriction components attributed to domain wall motion and rotation, the proposed model can accurately reproduce the butterfly loops in a wide range of magnetization along the rolling direction (RD) of GO material. Its effectiveness and accuracy are verified by the experimental measurements.

SPICE-Aided Models of Magnetic Elements—A Critical Review

This article analyzes the problem of modeling the properties of such magnetic elements as inductors, coupled inductors, and transformers using the SPICE software (version 17.2). Both the classical models of magnetic elements, built in this software, and the models implemented in the form of subcircuits are described. In particular, attention was paid to the possibility of taking into account the non-linearity of the characteristics of the considered elements and mutual couplings between electrical, magnetic, and thermal quantities. Using the results of thermographic measurements, the need to take into account the differences in temperature values between the individual windings and the core of inductors and transformers was justified. Selected models of the considered elements given in the literature are briefly characterized. The network structures of the electrothermal models of the considered elements elaborated at Gdynia Maritime University are presented. The results of calculations and measurements illustrating the correctness of the described models and their prac-tical usefulness for the elements of different structures are presented and discussed.

Comprehensive study on the through-process Goss texture evolution in Fe-3.78 wt.%Si grain oriented electrical steel

Cold rolled grain oriented steel is used in transformer cores due to its superior magnetic properties. Large Goss oriented grains develop after the final secondary recrystallization provide low hysteresis loss. The present study represents the development of Goss orientation after each processing stage of Fe-3.78 wt% Si steel with the help of electron backscatter diffraction and x-ray diffraction techniques. The Goss oriented grains developed during hot rolling and hot band annealing did not remain stable in cold rolling. On the other hand, shear bands developed inside {111}<112> component of γ-fiber texture during cold rolling. Partial recrystallization of the cold rolled sheet revealed that Goss oriented grains started evolving inside the shear bands of {111}<112> oriented grains. Intermediate annealing between cold rolling passes was found to be not essential to achieve Goss orientation in primary recrystallization. The optimum primary recrystallization temperature was in between 923 and 948 K where a significant amount of Goss oriented grains were present. Further, secondary recrystallization was attempted at different temperatures between 1173 and 1473 K. Grain boundary curvature of Goss oriented grains and all other grains after both primary and secondary recrystallization was studied. Despite the percentage of convex boundaries surrounding Goss oriented grains was found slightly higher than that around other grains, it was insufficient to cause abnormal grain growth.

Magnetic Flux Bias Compensation Based on Voltage Injection Method With an Auxiliary DC/DC Converter

DC bias will make the transformer core saturated, causing local overheating and insulation materials aging. Therefore, it is great of significance to study the suppression of DC bias in transformers. In this paper, a magnetic compensation scheme of DC bias based on a hybrid transformer (HT) integrated an auxiliary DC/DC converter is proposed. Firstly, a compensation mechanism is established by designing a novel HT topology structure, which lays the magnetic circuit foundation of DC bias compensation. Secondly, the mathematical model of transformer DC bias is established, and the DC compensation amount of HT is derived. A transient simulation model of three-phase HT is established by the finite element model, and the situation of the DC bias before and after the compensation is analyzed. Finally, the platform of the DC bias compensation scheme is built. The full compensation experiment of DC bias is simulated by two parallel HT. The experimental results show the DC bias compensation effect is obvious, the distortion of excitation current, temperature rise and flux density distribution drop obviously, which verifies the correctness of the scheme proposed in this paper. It provides a reference for solving the problem of DC bias.

A Low-Cost Battery-Balancing Auxiliary Power Module With Dual-Active Half Bridge Links and Coreless Transformers

Redistributive balancing brings many benefits to electric vehicles, such as increased range and more uniform cell degradation. Despite previous analyses suggesting a 17-36% extension of battery lifetime, the cost of such systems has prevented the technology from being adopted in practice. This study proposes a simplified topology for battery-balancing auxiliary power modules with reduced magnetic material to achieve cost-friendly solutions without sacrificing functionality or balancing modes. The proposed system consists of a dual-active half bridge, halving the number of switches needed compared with the conventional dual-active bridge. In addition, the transformer core material is removed and a coreless transformer is used to provide isolation and energy transfer. Both changes reduce the cost of redistributive balancing. The topological modeling differs from cored transformer circuits as the coupling of the coreless transformer is weaker. The coupling coefficient is now used in an updated model that includes transformer currents and output powers. These, along with the balancing modes, are analyzed then experimentally verified. The proposed models can guide the selection of MOSFETs and the design of the coreless transformer. An analytic projection shows up to a 22% cost reduction compared with similar topologies.

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.

(Digital Presentation) A Novel Electrochemical Reactor Design-2

(In this design emphasis is given particularly on the tube types of the secondary winding without much change in the previous description of the reactor)Different kinds of energies such as optical, thermal, mechanical etc. are used for carrying out chemical reactions.The following presentation deals with a simple and an innovative idea of utilization of electromagnetic energy for carrying out chemical reactions.Proposed here is an entirely different electrochemical reactor design with an innovative experimental setup which will give - or rather - is very likely to give interesting results while carrying out chemical reactions. The setup is a modified transformer. Unlike the conventional transformer which has a primary and a secondary coil of insulated copper wire wound on a transformer core; this suggested setup has a primary coil of copper, but the secondary coil is in the form of a tube in which a reaction mixture i.e. the reactants can be introduced as shown in Figure 1. Reactants that have at least some electrical conductivity are preferable. If not, provision can be made by adding compatible additives. On applying an alternating sinusoidal electric current in the primary coil; the reactants will directly receive energy by the phenomenon known as mutual electromagnetic induction from the primary coil which will/or should initiate, accelerate or aid the reaction.In the experimental setup we have:1) A primary coil of copper,2) A secondary coil in the form of a tube to carry the reactants,3) Variable frequency and amplitude of the alternating electric current to be applied to the primary coil,4) Type of waveform from the waveform generator,5) Provision to control the rate of flow of the reactants through the tubular secondary coil.By experimenting using the proposed setup, it is very likely that we well get some primary results. Based on these primary results/observations, the setup then can be further tuned down to get the desired results by choosing:1) Number of turns of the primary coil,2) Number of turns of the secondary tube coil carrying the reactants,3) Deciding the frequency, amplitude and the duration of the alternating electric current to be applied to the primary coil,4) Selecting the waveform from the waveform generator,5) Deciding the rate of flow of the reactants through the tubular secondary coil,6) Deciding the material and properties of the tube used in the secondary winding etc.Simultaneously, ultrasound, UV radiation, temperature (either cooling or heating) etc. can also be thought of as an application on the reactants contained in the secondary tube.A catalyst can be coated or inserted at proper locations and in proper shape inside the secondary tube.Different frequencies in a particular sequence and duration can also be applied at the input.The tube of the secondary may be: Transparent,Electrically non-conducting,Electrically conducting with insulation coating from outside,Or a combination of conducting - non-conducting - again conducting as shown in Figure 2,And of any such combinations using two or more types of tubes mentioned above. Such combinations of multiple tube types may prove to be beneficial (e.g. for simultaneous application of UV radiation through the transparent portion) and can be experimented on.Different types of transformer assemblies with secondary in the form of a tube to contain the chemicals can also be used. For example, multiple winding transformers which have two or more primary or secondary windings allowing for different combinations of voltages and current, three phase transformers etc.The reactor can be used to study various types of parameters in different types of chemical reactions such as:1) The study of frequency dependence on the rate of chemical reactions,2) Estimation of triggering frequencies for breaking of bonds in a reaction,3) The threshold of a chemical reaction in terms of frequency can also be tested by application of a triggering pulse at the input etc.Here we have an unusual secondary in a transformer wherein the secondary is a coil of reactants.Experimental validation of the reactor needs to be done which will require a team of experts in chemistry/electrochemistry, transformer designing etc. On reviewing the abstract, should any scientist or a group if scientists find the design intriguing, they are welcome to conduct further research using the proposed reactor design. A provisional patent has been filed for the same. Figure 1

Mathematical Modelling of Shear Cutting Process of Grain Oriented Electrical Steels Using Regression Modelling

This article proposes a regression model for the shear-cutting process of grain-oriented electrical steel magnetic cores of transformers made from different gages and magnetic properties of steels. In the experimental runs, 3 levels for thickness (230, 270, and 300 µm) and 4 levels for magnetic features of electrical steels are considered. Core steels are supplied as foils and slit to designed lengths in slitting machinery along the rolling direction of coils. The best magnetic features rely on the rolling direction of the coil and the transverse direction of the coil is subject to the shear-cutting process. The result of cutting operations, discontinuities, and degradations in magnetic properties may occur because of deterioration in crystallography and strain gradation on laminated sheets. Shear-cutting process factors have a strong influence on magnetic degradation even the magnitude of the no-load loss of the transformer core. In this study, the mathematical relation between shear cutting factors sheet thickness ST, counts of hits CH, and the response burr length BL is determined using regression modeling. For this purpose, the process parameters of GEORG TBA 400 cut-to-length machinery in use core production is studied. The calculated coefficient of determination is close to almost 1.00 i.e., R2 = 0.9896 which means the factors are sufficient to model the response, and the model is obtained with a good prediction performance. The aim of the present study is building up a useful process control tool for the machinery and raise a discussion alike process in industry.

Mathematical modeling and experimental research on grounding current calculation of converter transformer core

When the converter transformer core is grounded at multi-points, a fault loop will be formed and a circulation will be generated, leading to local overheating of the magnetic core and decomposition of insulating oil. Therefore, the converter transformer core will be single point grounded. As a rare internal lead of converter transformer, the ground current on the core ground lead can often reflect the running state of converter transformer. In this paper, theoretical analysis, modeling simulation and experimental research are carried out on the ground current of converter transformer at one point. Firstly, according to the structure characteristics of converter transformer, the analytical modeling of ground current is carried out. Secondly, based on the structure characteristics of oil paper insulation, the equivalent capacitance of converter transformer is calculated. Then, the analytical and finite element simulation model of converter transformer is established, and the ground current of converter transformer is calculated. Finally, the correctness of the proposed scheme is verified by measuring the grounding current of converter transformer core.

Numerical analysis of the impact of fin design and solar radiation on the cooling performance of a power transformer

In the present work, a three-dimensional model was performed to test a geometry and solar radiation effect on the cooling efficiency of a 250 kilovolt-ampere (kVA) oil-natural-air-natural (ONAN) electrical distribution transformer. Several fin shapes and other geometric aspects of the transformer were analyzed numerically (trapezoidal, wavy, and triangle fins).According to the findings, the trapezoidal fin shapes were the most effective in lowering the transformer's average surface and core temperatures, followed by the wavy fins and the triangular fins compared to the traditional transformer shape (straight fins). The study also showed that the temperature of the surface and the core of the transformer increases with increasing solar radiation, but the effect of high temperature as a result of electrical load is more influential than solar radiation. The results showed a significant convergence with previous research.&#x0D;

Effect of Preheating on the Mechanical Workability Improvement of High-Strength Electrical Steels during Tandem Cold Rolling

Cold-rolled silicon steel strip products are widely used as the main soft magnetic components in cores of electrical motors, generators, and transformers. In the case of rotating electrical machines, the so-called non-oriented electro-technical steels are normally applied. They are characterized by a similar behaviour to the induced magnetic field found in all sheet plane directions. The kind of soft magnetic alloys that defined herein not only possess an isotropy of electromagnetic properties, but also high mechanical strength; such alloys are called high-strength electro-technical (HSET) steels. These commercially produced HSET steels contain a high silicon content in the range of 3–4 wt.%. However, if the silicon content exceeds 3%, the machinability of Fe–Si alloys is dramatically reduced and they become much more brittle as a consequence. According to this, regular hot band brittle damage occurs during cold deformation at a high-speed tandem rolling mill. In accordance with these reasons, the production of thin high-strength silicon steel grades using the traditional methods of cold rolling deformation is extremely problematic and it is characterised by a high degree of steel sheet mechanical damage. In this scientific work, the effect of preheating hot-rolled strips on their mechanical workability improvement during tandem cold rolling was investigated. The results of this study indicate that the cold rolling of hot bands at elevated temperatures increases their resistance to brittle failure and mechanical plasticity. Moreover, the mathematical simulation clearly demonstrates that residual stress is distributed relatively homogeneously across the thickness of samples, which were cold rolled at 100 °C in contrast to the same ones deformed at room temperature.

A general strategy for direct growth of yolk-shell MOF-on-MOF hybrids

Construction of metal–organic framework (MOF) hybrids with yolk-shell nanostructures via MOF-on-MOF growth is significant for MOF design toward elaborate properties and enhanced performances, while remains challenging. Here, we report the direct growth of yolk-shell MOF-on-MOF hybrids via an interfacial growth-reorganization strategy. The synthesis relies on the precise growth of guest CoZn-ZIF (ZIF = zeolite imidazole framework) with appropriate crystal diameter and arrangement on host MOFs, inducing an in-situ transformation of core–shell intermediate into yolk-shell product. This strategy can be generally applied to the growth of CoZn-ZIF onto various host MOFs with different shapes, crystal structures and compositions including rod-like and octahedral Fe-based NH2-MIL-88B (MIL = Material Institute Lavoisier) and cake-like Ti-based NH2-MIL-125 toward three kinds of yolk-shell MOF-on-MOF hybrids. Moreover, functional carbon materials with bridged yolk-shell architecture can be prepared by pyrolysis of MOF-on-MOF hybrids as precursors, exhibiting enhanced oxygen reduction reaction performance than their monomeric counterparts. Our work paves the way for the design and application of MOF based yolk-shell nanostructures.

Design, manufacturing, and testing of 0.35/25kV, 20kHz transformers for particle accelerators.

A high voltage, high frequency transformer unit has been designed and built for powering the Cockcroft-Walton voltage multiplier to be used as part of a particle accelerator power supply at the Institute For Plasma Research, India, for the nuclear fusion research facility. A novel combination of high voltage (25kV), high frequency (20kHz), and high power (70kVA) specifications makes its design distinctive and more challenging. The complete unit is composed of two 0.350/25kV amorphous core transformers connected in center-tap configuration and immersed in an oil-filled tank. To facilitate an iterative design procedure, a spreadsheet method was utilized. The design involved a methodical approach for the core and winding selection, followed by the magnetic analysis and high voltage insulation layout through the finite element method. All the magnetic, electrical, and thermal parameters have been evaluated in detail, assuring a continuous stable operation having an efficiency of greater than 95%. Finally, the transformers were made, and preliminary experiments, including turns ratio, short-circuit, and dielectric tests, were carried out to verify the accuracy of the proposed design. The unit was also field tested under actual load conditions, and the test results were presented and corroborated with the design calculations.

Analytical formula of the mutual impedance of a partial core transformer with conductive tapes

The present work shows a first approximation of the analytical model of the mutual impedance of a transformer with a partial cylindrical core considering the effective tensor values of magnetic permeability and electrical conductivity. This first model is based on the use of constant values to represent the effective relative permeability of the core material of this transformer. The analytical expressions obtained allow modeling the mutual impedance values for the following cases: filamentary conductor, conductors with a rectangular cross-section and for a two-coil device.

Measurement of Magnetic and Magnetostrictive Characteristics of Transformer Core Based on Triaxial Strain Gauge and B-H Vector Sensor.

As is well known, the magnetostrictive phenomenon of electrical steel sheet is the main source of electricity in equipment such as transformers. The magnetostrictive characteristic of the actual transformer core is more complicated than that of single-sheet steel. The magnetostriction phenomenon of the transformer core cannot be fully understood by studying only a single piece of electrical steel, so it is necessary to study the local magnetic characteristics of the transformer directly. In this paper, two-limb, one-phase transformer core with a multi-step-lap construction was assembled, a laminated magnetostrictive testing system based on triaxial strain gauges was built, and the local magnetic characteristics were studied using a self-developed B-H vector sensor. The magnetostrictive and magnetic properties in different local regions were measured and analyzed under several magnetization patterns, and the influence of DC bias on the magnetostrictive property of the corner, yoke, and limb of the core was investigated. The influence of the position of the clamp on the magnetostriction of the transformer core was also studied. The magnetostrictive strain of the single sheet and laminated core was compared and discussed. The results showed that the strain caused by the interaction between laminations in this area can be effectively reduced when clamping in the middle of the yoke.

Soft Magnetic Properties and Electromagnetic Shielding Performance of Fe40Ni40B20 Microfibers

AbstractFe40Ni40B20 metallic glass is a key material among the many amorphous systems investigated thus far, owing to its high strength and appealing soft magnetic properties that make it suitable for use as transformer cores. In this study, Fe40Ni40B20 microfibers are fabricated down to 5 µm diameter. Three different melt–spinning wheel velocities: ≈51 m s−1, ≈59 m s−1, and ≈63 m s−1 (MG1, MG2, MG3) are used. Their fully amorphous structure is confirmed using X–ray diffraction, and differential scanning calorimetry (DSC) traces reveal a larger relaxation profile for the higher–quenched microfiber. Vibrating sample magnetometer measurements showed a higher saturation magnetization of 136 emug−1 for annealed metallic glass microfibers with a wheel velocity of 59.66 ms−1. Cylindrical magnetic field shields are obtained by aligning and wrapping the fibers around a cast. The observed anisotropic static field shielding behavior is in accordance with the microfibers' anisotropic nature. Composite samples are also produced by embedding the microfibers in an epoxy matrix to investigate their electromagnetic properties at GHz frequencies. Inclusion of the microfibers increase the composite's attenuation constant by 20 to 25 times, making it an ideal candidate for applications in the communications frequency range.

Ferrite Nanoparticles as Catalysts in Organic Reactions: A Mini Review

Ferrites have excellent magnetic, electric, and optical properties that make them an indispensable choice of material for a plethora of applications, such as in various biomedical fields, magneto–optical displays, rechargeable lithium batteries, microwave devices, internet technology, transformer cores, humidity sensors, high-frequency media, magnetic recordings, solar energy devices, and magnetic fluids. Recently, magnetically recoverable nanocatalysts are one of the most prominent fields of research as they can act both as homogeneous and heterogenous catalysts. Nano-ferrites provide a large surface area for organic groups to anchor, increase the product and decrease reaction time, providing a cost-effective method of transformation. Various organic reactions were reported, such as the photocatalytic decomposition of a different dye, alkylation, dehydrogenation, oxidation, C–C coupling, etc., with nano-ferrites as a catalyst. Metal-doped ferrites with Co, Ni, Mn, Cu, and Zn, along with the metal ferrites doped with Mn, Cr, Cd, Ag, Au, Pt, Pd, or lanthanides and surface modified with silica and titania, are used as catalysts in various organic reactions. Metal ferrites (MFe2O4) act as a Lewis acid and increase the electrophilicity of specific groups of the reactants by accepting electrons in order to form covalent bonds. Ferrite nanocatalysts are easily recoverable by applying an external magnetic field for their reuse without significantly losing their catalytic activities. The use of different metal ferrites in different organic transformations reduces the catalyst overloading and, at the same time, reduces the use of harmful solvents and the production of poisonous byproducts, hence, serving as a green method of chemical synthesis. This review provides insight into the application of different ferrites as magnetically recoverable nanocatalysts in different organic reactions and transformations.

Single-Ended Forward-Flybaсk Stabilized DC-DC Voltage Converter. Part. 1: Converter’s Power Stage

The article addresses the development of a single-ended single-transistor forward-flyback DC voltage converter. The classification of single-ended DC voltage converters is given, and their basic advantages and drawbacks are listed. In the first part, a new power stage structure of the converter being developed is proposed, which makes it possible to exclude pulsed overvoltages without power-dissipating protective RCD circuits caused by the transformer winding leakage inductance. The operation principle of the new power stage structure is described. The requirements posed to the magnetic cores of transformers for the new structure are described. The proposed scheme was investigated using computer simulation in the PSpice software. The computer model and time curves of the processes confirming the operability of the scheme are presented. The results of studying the effect the coupling coefficient between the transformer windings has on the overvoltage and cross instability are presented. The proposed power part structure of the forward-flyback DC voltage converter makes it possible to obtain a higher power output compared with the known single-ended forward-flyback power stages; it retains the operability in a wide variation range of the coupling coefficient between the transformer windings and provides high efficiency.

Measurement of surface vibration signal of 500 kV transformer and analysis of its frequency characteristics

Abstract By measuring and analyzing the vibration signals of the transformer core and windings, the operating conditions of the transformer can be diagnosed. In this paper, the surface vibration signals of 500 kV autotransformer with different structures are measured, and the frequency domain characteristics of the surface vibration signals are analyzed. The blind source separation algorithm is used to separate the surface vibration signals and obtain the vibration signals of core and winding respectively, which provides strong data support for further condition evaluation and fault diagnosis of the core and winding using their vibration signals. Firstly, the surface vibration signal measuring points are set according to the specific arrangement of the core and winding of the transformer; secondly, the vibration signals of different vibration measuring points of the transformer under the same load and different loads of the same vibration measuring point are measured respectively; finally, the frequency characteristics of the measured vibration signals are compared and analyzed. Then, use blind source separation algorithm for transformer surface vibration signal processing, the two signals obtained are close to the vibration characteristics of core and winding respectively, and the separated, it is proved that the accurate vibration signals of core and winding can be obtained by blind source separation, it is helpful for further analysis of the operation state of the core and winding.