Increase In Core Loss Research Articles

DC bias impact analysis on the capability of power transformer and failure risks

A significant transition towards low-carbon, renewable energy sources and technological adaptation is mandatory in the present scenario to address climate change and achieve a sustainable energy system. Aligned with the upgradation in technology, as the need for efficient and smart energy grows, power electronics are being extensively used in power systems. Various factors can affect the pervasive use of power electronics associated with power transformers, thereby introducing the DC bias in the system. DC bias in the transformer leads to a shift in operating point, a rise in excitation current and a generation of harmonics. This causes an increase in core losses and temperature, resulting in exceeding the thermal limits and leading to transformer failure. Consequently, there is an emergency need to understand the DC bias capability of power transformers that aims at optimal transformer selection without being overrated. This research employs Ansys maxwell software to model and simulate a 500 kVA, 11kV/420V three-phase power transformer. The experimental investigation is carried out through a scale-down value of a 5 kVA laboratory prototype. The research findings revealed a significant negative impact of DC bias on power transformer capabilities that could be detrimental to its performance, health and lifespan. The analysis results provide valuable insights for the design engineer during the initial stages of designing a high-performance, cost-effective transformer with a low failure rate.

A model to account for magnetic permeability changes resulting from edge damage caused by laser cutting in a high performance cobalt-iron alloy

Laser cutting is the mainstay of electrical machine stator core manufacture for prototyping and for high value, small and medium batch sizes. However, it can introduce localized damage into electrical steels, with reduction in magnetic permeability and increase in core loss in regions adjacent to the edge. These phenomena have been studied in Silicon-iron alloys, but there is little published data on Cobalt-iron. This paper presents experimental measurements on magnetic edge damage effect in Cobalt-iron alloys due to laser cutting. The paper then uses magnetic measurements for an increasing number of cuts in test samples to develop a model that represents the deterioration of magnetic permeability with distance from the cut edge, including cumulative damage effects from multiple cuts. The model is suitable for incorporation into finite-element models, either as a continuous function of position or to generate individual magnetization curves for discrete layers in finite-element mesh. The paper concludes by using the model to generate a series of magnetization curves which include the damage effect and in turn uses these to predict the net magnetic behavior of a series of rectangular strips. Good agreement is obtained between these predictions and measurements of samples from the same batch of Cobalt-iron.

CMT and GTA welding on microstructural characteristics and magnetic performance of thin CRNO electrical steel sheets

The Cold-Rolled Non-Oriented (CRNO) electrical steel of M − 45 grade are widely employed in medium capacity rotating electrical systems and small motors. The present work is based on the investigations performed on the CRNO electrical steel core samples welded on 6 sides around the outer periphery using Cold Metal Transfer (CMT) and Gas Tungsten Arc Welding (GTAW) process. The welded toroidal core samples were investigated for analyzing the alterations in magnetic properties and core losses by varying the magnetic flux density. In addition, the microstructure, residual stress and microhardness evaluation of the weld samples were also performed. The investigation on magnetic property revealed an considerable increase in core losses (W/Kg) affecting the magnetic performance, with coarse sized grains, drastic variations in hardness and residual stress in the weld affected region of the GTAW welded samples were noticed, in comparison to the CMT welded sample.

Fe-Based Amorphous Magnetic Powder Cores with Low Core Loss Fabricated by Novel Gas-Water Combined Atomization Powders.

FeSiBCCr amorphous powders were produced by a novel gas–water combined atomization process, and the corresponding MPCs (magnetic powder cores) were subsequently fabricated by phosphating treatment (0.4~1.6 wt.%), cold pressing (550~2350 MPa), and annealing (423~773 K), respectively. The results showed that the powders had high circularity, excellent thermal stability (ΔT = 59 K), and high saturation magnetization (0.83 T), which could provide raw powders for high-performance MPCs. With increasing phosphoric acid concentrations, despite the increase in DC-bias%, the uniformity of the insulation layers deteriorated, which led to a decrease in permeability and an increase in core loss. With increasing compaction pressures, the core loss increased continuously, and the permeability and DC-bias% first increased and then decreased. When annealing below the crystallization temperature, with increasing annealing temperatures, the permeability increased, and the core loss and DC-bias% decreased continuously. Under the optimized process of 0.4 wt.% phosphating concentration, 550 MPa pressure, and 773 K annealing temperature, the MPCs had a permeability of 21.54 ± 1.21, DC-bias% of 90.3 ± 0.2, and a core loss (Bm = 50 mT, f = 100 kHz) of 103.0 ± 26.3 mW cm−3. The MPCs had excellent high-frequency low-loss characteristics and showed great application potential under the development trends of high current, high power, and high frequency of electronic components.

The effects of post-processing on longitudinal magnetostriction and core losses of high saturation flux density FeSiBC amorphous alloy ribbons and cores

Fe-based amorphous soft magnetic materials play an attractive role in energy saving and emission reduction due to low core losses. One of the problems is the acoustic noise resulting from magnetostriction during AC magnetization process. In this work, amorphous ribbons with a nominal composition of Fe81.5Si4B14C0.5 (at. %) were produced by planar flow casting and subjected to various postprocessing treatments. The influences of annealing conditions on the longitudinal magnetostriction, acoustic noise and core losses of the ribbons measured at low-field were studied. The effects of bending stress and epoxy impregnation and curing on medium frequency core losses of the alloy cores with different shapes were also investigated. It is shown that larger longitudinal magnetostriction of amorphous ribbons leads to higher acoustic noise emission from amorphous cores. Although the longitudinal magnetostriction was found to be reduced by applying a longitudinal magnetic field during annealing, the core loss was increased. The minimum longitudinal magnetostriction value at 1000 A/m is 7 ppm for ribbon annealed at 350 °C for 90 min. under an applied longitudinal magnetic field, while the lowest core losses at 1.4 T and 50 Hz is 0.213 W/kg for toroidal core annealed at 350 °C for 90 min. under an applied transverse magnetic field. The coupling between longitudinal magnetostriction and bending stress of amorphous ribbon results in an increase in core losses. Furthermore, extra stress was introduced after epoxy impregnation and curing, which also results in an increase in core losses. Thus, low longitudinal magnetostriction is important for stress insensitivity and soft magnetic properties.

FUNCTIONAL TESTING OF THIN AND STACK WELDED M400-50 A5 CRNGO ELECTRICAL STEEL

In this paper, the effect of gas tungsten arc (GTA) welding current on the mechanical–microstructural–magnetic (M[Formula: see text] properties of cold-rolled non-oriented electrical steel (CRNGO) are investigated. The thin CRNGO sheets of 0.5[Formula: see text]mm each are stacked, welded at a different range of welding current from 30 A to 110 A, and observed for mechanical testing (joint performance and micro-hardness), macroscopic (weld seam characterization), microscopic (grain size variation), and magnetic property evaluation of post-welded samples. The results showed that with the increase in weld current, significant variation in micro-hardness, weld strength, weld seam size, and grain size in the samples’ weld zone is observed. A massive increase in core loss and magnetic field strength, with a significant decrease in relative permeability, is observed for the welded samples compared to the non-welded sample. The samples’ weld strength was varying, depending on the size of the HAZ and fusion zone (FZ) region, for a different weld current range. The hardness in the samples’ weld region increases with the weld current, with relatively higher hardness values observed at the FZ region of weld. Besides, it is observed that the increase in weld current resulted in the formation of coarse-sized grains in the HAZ region of the weld sample, with fine grains existing at the FZ region for higher weld current. The study can be referred for determining the appropriate welding parameters for joining of stacked CRNGO sheets to achieve the desired material properties.

Investigations on Magnetic and Corrosive Characteristics of Thin Cold-Rolled Nonoriented Electrical Steel Sheets Post Gas Tungsten Arc and Laser Welding

Abstract Thin sheets (0.5 × 10−3 m) of cold-rolled nonoriented (CRNO) electrical steel are widely used for rotating electrical machines. Gas tungsten arc (GTA) and, recently, laser welding are used for welding M-43 grade CRNO steel. The performance of CRNO is thus explored because of changes in low-carbon, high-silicon content and thin insulation coatings post welding. The welding current for GTA varied from 30 to 110 A, whereas a laser of 800 W was used to estimate the heat affected zone (HAZ), fusion zone (FZ), and weld characteristic ratio. Ferritic phases with polygonal grain size, percent silicon content, magnetic losses, and welded corrosive samples corrosion rate (in mils penetration per year) are compared with the base material (average grain size 55 ± 12 μm). Five different corrodent (NaCl, NaOH, HCl, H2O, H2CO3) environments were created for 2,000 h as per ASTM B895-16(2020)e1, Standard Test Methods for Evaluating the Corrosion Resistance of Stainless Steel Powder Metallurgy (PM) Parts/Specimens by Immersion in a Sodium Chloride Solution, and ASTM G31-72(1999), Standard Practice for Laboratory Immersion Corrosion Testing of Metals standards. The GTA weld samples revealed much-increased weld geometry with welding current, and a significant increase in grain sizes up to 189.2 ± 4 μm for GTA and 187 ± 3 μm for the laser sample near the weld zone is observed. Microhardness variation is found to be in the range of 55 HV for GTA and 51 HV for laser samples in the FZ region with reference to the base metal hardness of 227 HV. In addition, the increase in core loss of 58.72 % for GTA and 39.82 % for laser samples with reference to nonwelded samples is observed.

Effects of Laser Cutting on Microstructure and Magnetic Properties of Non-Orientation Electrical Steel Laminations

Non-oriented electrical steel (NOES) is commonly used as a core material in electric machines. These laminations are cut into the desired core shape that modifies the material properties near the cut edge, which consequently changes the magnetic performance of the core lamination. Magnetic property deterioration due to cutting has been reported in the literature but less attention has been given to the microstructural changes due to cutting and its relation to the magnetic properties. The present research focuses on the effects of laser cutting on microstructure and magnetic properties of NOES laminations. A number of lamination steel samples were laser-cut using an identical procedure to that expected on an industrial scale. Property measurements showed that the magnetic permeability of the samples decreased while the core losses increased. The core loss increase was significant, about 22% at 50 Hz and 1.5 T. This was attributed to the change in the micromagnetic characteristics of the sample due to cutting. The change in micromagnetics was investigated using magnetic domain imaging and distorted domain structure was observed near the laser-cut edge. Backscattered electron imaging and nanoindentation measurements were also used for further investigation of micromagnetic properties of the material.

Design of 3D-Printed Hybrid Axial-Flux Motor Using 3D-Printed SMC Core

Axial-flux permanent-magnet synchronous motors (AFPMSMs) have a higher torque density than radial-flux permanent-magnet synchronous motors (RFPMSMs); therefore, AFPMSMs are widely used in high-power and high-efficiency motors. However, in the case of AFPMSMs, three-dimensional production is limited, less mass production is available, and the production unit cost is high because the shape of the motor is implemented by rolling the amorphous electrical steel sheet or molding the soft magnetic composite (SMC) to manufacture the motor. Therefore, in this paper, a 3D-printed AFPMSM is proposed, which takes high torque density including the AFPMSM shoe to mold existing SMC into shape when producing the AFPMSM using 3D printing. Further, hybrid AFPMSM, which is made by heeding, is proposed. To reduce core loss with 3D-printed AFPMSM, the core loss of the proposed hybrid AFPMSM was compared to that of the target RFPMSM in this study. The 3D-printed AFPMSM showed a 48% increase in core loss compared to the target motor. However, the proposed hybrid AFPMSM reduced the ratio of the electrical steel sheet by more than 25% compared to 3D-printed AFPMSM. The validity of the proposed model was verified using the finite element method.

Effect of Laser Cutting on Core Losses in Electrical Machines—Measurements and Modeling

Cutting of the electrical steel sheets to appropriate shape and size is performed during the manufacturing of electrical machines that leads to the magnetic material deterioration near the cutting edge. Epstein frame measurements of electrical steel samples of different widths cut by laser cutting are carried out in the range of 20–400 Hz frequency of sinusoidal excitations. Two stators one with laser cut and another one with electric discharge wire cutting are manufactured and the effect of cutting on core losses is analyzed. The effect of cutting on the magnetic permeability and core losses are modeled with analytical equations. Furthermore, the model is implemented in the finite-element (FE) simulation of the Epstein frame test setup. The presented loss model is found to reproduce the measurement results reasonably. The loss model is then applied to the simulation of a cage induction machine with time-stepping FE analysis (FEA). A significant increase in core losses was observed both in simulations and measurements due to the effect of laser cutting. The presented cutting model closely follows the measured core losses.

Microstructural evolution and magnetic properties in strip cast non-oriented silicon steel produced by warm rolling

In this study, a specific warm rolling was implemented to process Fe-2.8%Si steel by novel twin-roll strip casting. The impact of warm deformation on mechanical behavior, microstructural evolution and magnetic properties is presented. The study indicated that dynamic strain aging (DSA) occurred in the temperature range of 150–300 °C. The elevated rolling temperature strengthened DSA effect and promoted the formation of shear bands. The nucleation process of Cube ({100} 〈001〉) grains during annealing was weakened on introducing warm rolling, while that of Goss grains ({110} < 001>) was enhanced. Moreover, the recrystallization texture pattern of (Cube + Goss) gradually transformed into a pattern of only pronounced Goss texture. The corresponding values of magnetic induction B50 at rolling direction and transverse direction were obviously improved. This confirms the feasibility of processing ultra-high-permeability non-oriented silicon steel based on twin-roll strip casting combined with DSA-control rolling. However, the rolling process increased the nucleation site for recrystallization and decreased the size of precipitates in annealed sheet, leading to a reduction in grain size and an increase in core loss.

Core loss in magnetic rings made of Fe16N2-like iron nitride powder

The soft magnetic properties of α-Fe fine powders were investigated before and after low temperature ammonolysis together with the effect of alumina presence in the grain boundaries to clarify the contribution of these during the preparation process. The crystallite size was controlled to be approximately 50 nm and 30 nm before and after ammonolysis, respectively, by changing the preparation conditions to eliminate the effect of particle size on the magnetic properties. The ammonolysis product was a mixture of approximately 50 wt% of an α″-Fe16N2-like compound (hereafter denoted as “α″-Fe16N2”) with residual α-Fe, which had the largest magnetization among the ammonolysis products reported in our previous works. The core loss of magnetic rings made from this powder was first studied after sealing in Delrin® capsules to avoid decomposition by oxidation and the presence of humidity. The core loss was decreased to one third and the permeability was decreased to approximately 80% by the ammonolysis process, independent of the presence of alumina at the grain boundaries. The hysteresis contribution in the core loss was significantly decreased due to enhanced magnetic domain interaction in the anisotropic crystal lattice of “α″-Fe16N2”. The covalent chemical bonds of Fe-N caused the compound to be more electrically resistive and also resulted in a slight decrease of the eddy current loss contribution. Alumina precipitation at the grain boundaries caused a doubling of core loss increase and an increase of the permeability to approximately 130% because the magnetic interaction between grains was reduced by the presence of alumina in the composite products. Combing the decreased core loss by nitridation and the increased magnetic permeability by alumina precipitation will be useful to develop a new soft magnetic material.

Origin and Quantification of Increased Core Loss in MnZn Ferrite Plates of a Multi-Gap Inductor

Inductors realized with high permeable MnZn ferrite require, unlike iron-powder cores with an inherent dis-tributed gap, a discrete air gap in the magnetic circuit to prevent saturation of the core material and/or tune the inductance value. This large discrete gap can be divided into several partial gaps in order to reduce the air gap stray field and consequently the proximity losses in the winding. The multi-gap core, realized by stacking several thin ferrite plates and inserting a non-magnetic spacer material between the plates, however, exhibits a substan-tial increase in core losses which cannot be explained from the intrinsic properties of the ferrite. In this paper, a comprehensive overview of the scientific literature regarding machining induced core losses in ferrite, dating back to the early 1970s, is provided which suggests that the observed excess core losses could be attributed to a deterioration of ferrite properties in the surface layer of the plates caused by mechanical stress exerted during machining. However, in a first experimental analysis no structural evidence for a deteriorated layer close to the surface is identified by means of Scanning Electron Microscopy (SEM). Therefore, in a next step, a new calorimetric measurement setup based on temperature rise monitoring is proposed in this paper in order to quantify and differentiate between core losses associated with the bulk and the surface of the ferrite plates and therefore to pinpoint the measured excess core loss to shallow layers of ferrite with deteriorated magnetic performance. Electrical measurement of the surface related core losses utilizing the widely accepted two-winding wattmeter method with reactive power compensation is outlined in the appendix but was not employed in this work due to comparably low measurement accuracy. By means of the proposed measurement technique, the bulk and surface core loss density of the MnZn ferrite material 3F4 from FerroxCube was determined for sinusoidal flux density amplitude varying from 75 mT up to 200 mT and excitation frequencies ranging from 200 kHz to 1 MHz. The measured core loss densities (W/cm 3 ) show good agreement with the Steinmetz model provided by the manufacturer validating the proposed calorimetric core loss measurement technique. The measured surface loss density (W/cm 2 ) can also be well predicted with a Steinmetz model, whereby the frequency exponent α in the surface is slightly smaller and the flux density exponent β is slightly larger compared to the Steinmetz parameter of the bulk ferrite. It is shown that the ratio between surface and bulk core losses of a composite core assembled from individual plates is only a function of plate thickness and does not depend on the actual cross section area. Critical plate thickness is then defined to be reached when the total power loss in the composite core has doubled compared to a solid (single-piece) core sample. This new quantity provides a very helpful figure for multi-gap inductor designs. Besides the deteriorated surface layers, several other mechanisms potentially contributing to increased core losses in multi-gap inductors were identified and are finally discussed in the appendix of this paper: flux crowding in the core due to tolerances and imperfections in machining and assembly; deterioration of ferrite properties due to pressure buildup in the stack of plates during the curing of the employed epoxy resin; ohmic loss in the ferrite associated with the current flowing in the conduction path provided by the low impedance of the ferrite material at high frequencies and the parasitic capacitance between winding and the ferrite core.

The thermal and magnetic properties of the Fe89.8Ni1.5Si5.2B3C0.5 and Fe81B13Si14C2 amorphous alloys

This paper investigates the thermal and magnetic properties of two iron based amorphous alloys with different Fe-content: Fe89.8Ni1.5Si5.2B3C0.5 and Fe81B13Si14C2. The XRD results show that the thermal induced structural changes occur in the temperature range of 3000C - 8500C for the Fe89.8Ni1.5Si5.2B3C0.5 amorphous alloy. The appearance of the first crystallization peaks on DSC thermograms of Fe81B13Si4C2, amorphous alloy is perceived already at 4500C. The initial magnetization curves of the as-cast sample of the Fe89.8Ni1.5Si5.2B3C0.5 amorphous alloy, obtained at the frequencies of 50 Hz, 400 Hz and 1000 Hz show the excellent match. The maximum relative magnetic permeability for Fe89.8Ni1.5Si5.2B3C0.5 alloy sample is achieved at magnetic field strength of about 20 A/m for all frequencies, whereas the values of about 7000 were obtained at the frequencies of 50 Hz and 400 Hz. The influence of frequency on total power losses, for both alloys exhibits the increase of core losses with frequency increase. The amorphous alloy Fe89.8Ni1.5Si5.2B3C0.5 toroidal core exhibits about 3 time higher total power losses.

Degradation of Magnetic Properties in Transformer Steel: Role of Prior Elastic Deformation

Transformer steel, fully processed Hi-B (high permeability) grade of cold rolled grain oriented (CRGO), was subjected to relatively minor, 0 to -55 MPa, stresses. Detailed magnetic and microstructural characterizations were then carried out. Shift of hysteresis loop and clear degradation in magnetic properties, namely increase in core loss and drop in permeability, were noted. Though absence of mesoscopic plastic strains was confirmed, possibilities of minor local plastic deformation cannot be ruled out. Prior deformations: 1) modified residual strain/stress signatures in both CRGO laminates and Forsterite (Mg <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> ) coating and 2) caused corresponding degradation in magnetic performance. Redistribution of residual stresses through local plastic deformation appears to be the plausible justification for these observations. This paper brought out clear correlations between degradation in magnetic properties with introduced residual stress/strain.

Possible influence of sulfur content on magnetic aging behaviors of non-oriented electrical steels

Six non-oriented steel sheets of similar grade produced by different steel companies were used to analyze the magnetic aging behaviors after aging at 200°C for 48 h. It was observed that tiny S atoms, besides C and N, could also induce certain increase of core loss during aging. Thermodynamic calculation indicated that the nucleation driving force of FeS is much higher than those of Fe3C and Fe4N at low temperature, while S atoms, which tend to segregated around dislocations and boundaries, would diffuse rapidly along the crystalline defects while FeS particles would form. Therefore, higher content of tiny S atoms could increase core loss during service time of non-oriented steel sheets.

Harmonic Balance Based Stability Domain Analysis of Period-1 Ferroresonance

In an attempt to find regions at risk of ferroresonance, different time-domain simulations and analytical approaches were investigated on a one-phase laboratory transformer. A 2D bifurcation diagram based on a one-term harmonic balance method has been developed. It was shown that increase of core losses during over-voltages significantly affects the stability domain of period-1 ferroresonance. Time-domain simulations show that a static core loss model as a function of the maximum flux of the transformer predicts the second bifurcation point with enough accuracy. This modeling approach was incorporated in harmonic balance analysis. A comparison has been made between analysis and measurements.

Estimation of core losses under sinusoidal or nonsinusoidal induction by analysis of magnetization rate

This work deals with a method of analysis that estimates the increase of core losses under sinusoidal and nonsinusoidal inductions. The estimation can be carried out by correlating instantaneous magnetization power (PM) or the instantaneous magnetic field (H) as a function of the magnetization rate (dB/dt) and the induction level (B). Experimentally, this correlation can be obtained under triangular waveform induction tests. Predictions under sinusoidal and nonsinusoidal inductions were made in oriented and nonoriented FeSi steel sheets. The predictions, when compared to experimental results, show an error of up to 3% for nonoriented materials and of up to 5% for oriented materials. Also, this method allows the prediction of the loss loop shapes. The limitations and perspectives of the method are considered in this work.

Estimation of Core Losses under Sinusoidal or Nonsinusoidal Induction by Analysis of Magnetization Rate

This work deals with a method of analysis that estimates the increase of core losses under sinusoidal and nonsinusoidal inductions. The estimation can be carried out by correlating instantaneous magnetization power (PM) or the instantaneous magnetic field (H) as a function of the magnetization rate (dB/dt) and the induction level (B). Experimentally, this correlation can be obtained under triangular waveform induction tests. Predictions under sinusoidal and nonsinusoidal inductions were made in oriented and nonoriented FeSi steel sheets. The predictions, when compared to experimental results, show an error of up to 3% for nonoriented materials and of up to 5% for oriented materials. Also, this method allows the prediction of the loss loop shapes. The limitations and perspectives of the method are considered in this work.

磁性材料 直流送電システム用アノードリアクトル圧粉磁心

Anode reactor powder cores are used to protect Thyristor Valves of HVDC (High-Voltage Direct Current)transmission systems. They must have a long life under special conditions of high frequency and high magnetic flux density. Thus, they should have the properties of low core loss, constant permeability, high saturated flux density, and excellent heat resistance.To develop them, we studied on formation methods and compositions of uniform inorganic insulation films on each powder, and on selection and additive conditions of resin. As the results, we have developed the new anode reactor powder cores which shows specific resistivity of more than 1 Ωm, which is above twenty times of usual powder cores, and saturation flux density of more than 1T. They show scarcely increase of core loss after 4000 hours at 423 K, which means that they indicate excellent heat resistance.