Bonded Terfenol-D composites with low eddy current loss and high magnetostriction

Bonded Terfenol-D composites,with high electrical resistivity and low eddy current loss,can be used in an alternating magnetic field with high frequency.However,the nonmagnetic binder impairs the magnetostriction of the composites.To achieve high magnetostriction and low eddy current loss,the mixture of the alloy powder and binder was compressed at low pressure in an oriented magnetic field.After this,the aligned samples were recompressed by cold isostatic pressing（CIP）.Besides,the effect of particle size on the magnetostriction of the bonded Terfenol-D composites was also studied.The results showed that the bonded Terfenol-D composites had excellent magnetostriction when the particle size was 50-80 μm.The oriented magnetic field and CIP could improve the magnetostriction of the bonded composites,which reaches 1020×10-6.The bonded Terfenol-D composites had good compact structure and high density（7.24 g/cm3）.The magnetic loss of the bonded Terfenol-D composites was 192 mW/cm3 at a frequency of 100 kHz in a magnetic field of 960 A/m,which was about one third of that of casting Terfenol-D alloys.

Experimental Study of Current Loss of Stainless Steel Magnetically Insulated Transmission Line with Current Density at MA/cm Level

A magnetically insulated transmission line （MITL） is used to transmit high power electric pulses in large pulse power systems. However, current loss is unavoidable, especially when the current density is up to 1 MA/cm. In the paper, the current loss of an MITL made of stainless steel, which is usually used in large pulse power generators, is experimentally studied, and possible mechanisms to explain the current loss of the MITL are analyzed and discussed. From the experimental results, the relationship between loss current density and input current density follows approximately a power law. The loss is also related to the configuration of the MITL.

Experimental study of current loss of a single-hole post-hole convolute on the QG I generator

The post-hole convolute(PHC),which is used to transport and combine the pulse power flux,is a key component in huge pulsed power generators.Current loss at the PHC is a challenging problem for researchers.To explore a method of reducing the current loss,a single-hole PHC was designed for experiments on the current loss on the Qiang Guang I generator.The experimental results showed that the current loss at the single-hole PHC is related to the distance/between the vicinity of the cathode hole and the surface of the downstream side of the post.Meanwhile,a single-hole PHC with a blob cathode hole transmitted current more effectively than the PHC with a circle cathode hole.The relative current loss at the single-hole PHC with the cathode coaled w ith gold foil was about 30%-50% of that with the cathode coated with nickel and titanium foil.The gap closing speed was also obtained from the current waveforms in the experiments.The speed was 5.74-14.52 cmμs 1 which was different from the classical plasma expansion velocity of 3 cmμs 1.

Novel Rotors with Low Eddy Current Loss for High Speed Permanent Magnet Machines

Due to the large rotor eddy current loss and low thermal conductivity of carbon fiber sleeve,the high temperature usually occurs in high speed permanent magnet machines(HSPMMs)at the rated operation condition,resulting in irreversible demagnetization of the permanent magnet(PM).To obtain low rotor temperature,two novel rotor structures with low rotor eddy current loss are proposed in this paper.With the output torque and air gap flux density unchanged,the performance of HSPMMs with the two proposed rotor structures are analyzed based on finite element algorithm(FEA),including eddy current loss and temperature.Finally,the appropriate parameters of the proposed rotor structures are selected,and the electromagnetic(EM)performance,rotor stress and temperature are compared with those of the conventional rotor structure.Index Terms-Eddy current loss,finite element algorithm(FEA),electromagnetic(EM)performance,high speed permanent magnet machines(HSPMMs).

Visualization and Quantitative Evaluation of Eddy Current Loss in Bar-Wound Type Permanent Magnet Synchronous Motor for Mild-Hybrid Vehicles

This paper describes the conductor eddy current loss that occurs in a permanent magnet type synchronous motor with a distributed winding stator using a rectangular copper wire designed for mild hybrid system applications for small vehicles.Compared with the conventional round wire inserter method,the space factor can be improved and the coil-end length can be shortened by applying a so-called hairpin windings using a pre-formed into hairpin shape of bar conductor,and as a result,DC current resistance of the armature winding can be reduced.However,since the conductor cross-sectional area tends to increases,the conductor eddy current loss generated by the space harmonics linkage becomes too large to ignore.In order to study the reduction of the conductor eddy current loss,it is important to visualize the spatial leakage flux distribution which causes loss and finely analyze how the magnetic path is formed.Therefore,analysis of the conductor eddy current loss distribution generated in the bar-wound conductor is performed using the CAE model that faithfully reproduces the coil-end shape of the actual machine.Furthermore,it was qualitatively clarified what ratio of conductor eddy current loss at various driving points.Finally,the results of preliminary study on reduction of conductor eddy current loss are reported.

Alternating-current losses in two-layer superconducting cables consisting of second-generation superconductors coated by U-shaped ferromagnetic materials

Alternating-current losses in a two-layer superconducting cable, each layer being composed of 15 closely-spaced rectangular wires made up of second-generation superconductors when the ends of wires are coated by either a non-magnetic or strong ferromagnetic material having a U profile is numerically investigated. Computations are carried out through the finite-element method. The alternating-current losses do not increase significantly if the relative permeability of the coating is increased three orders of magnitude, provided that the current amplitude is less than half of the critical current in a superconducting wire. However, the losses are much higher for ferromagnetic coating if the amplitude of the applied current oscillating at 50 Hz is close to the critical current. The ferromagnetic coating is seen to accumulate the magnetic field lines normally on its surfaces, while the field lines are parallel to the long axes of the wires, leading to more significant flux penetration in the coated regions. This facilitates a uniform low-loss current flow in the uncoated regions of the wires. In contrast, coating with a non-magnetic material gives rise to a considerably smaller current flow in the uncoated regions, whereas the low-loss flow is maintained in the coated regions. Moreover, the current flows in opposite directions in the coated and uncoated regions, where the direction in each region is converse for the two materials.

Current loss of magnetically insulated coaxial diode with cathode negative ion

Current loss without an obvious impedance collapse in the magnetically insulated coaxial diode （MICD） is studied through experiment and particle-in-cell （PIC） simulation when the guiding magnetic field is strong enough. Cathode nega- tive ions are clarified to be the predominant reason for it. Theoretical analysis and simulation both indicate that the velocity of the negative ion reaches up to 1 cm/ns due to the space potential between the anode and cathode gap （A-C gap）. Accord- ingly, instead of the reverse current loss and the parasitic current loss, the negative ion loss appears during the whole pulse. The negative ion current loss is determined by its ionization production rate. It increases with diode voltage increasing. The smaller space charge effect caused by the beam thickening and the weaker radial restriction both promote the negative ion production under a lower magnetic field. Therefore, as the magnetic field increases, the current loss gradually decreases until the beam thickening nearly stops.

Investigation on current loss of high-power vacuum transmission lines with coaxial-disk transitions by particle-in-cell simulations

Coaxial-disk transitions can generate non-uniform magnetic fields and abrupt impedance variations in magnetically insulated transmission lines(MITLs),resulting in disturbed electron flow and non-negligible current loss.In this paper,3 D particle-in-cell simulations are conducted with UNPIC-3 d to investigate the current loss mechanism and the influence of the input parameters of the coaxial-disk transition on current loss in an MITL system.The results reveal that the magnetic field non-uniformity causes major current loss in the MITL after the coaxialdisk transition,and the non-uniformity decreases with the distance away from the transition.The uniformity of the magnetic field is improved when increasing the number of feed lines of a linear transformer driver-based accelerator with coaxial-disk transitions.The number of input feed lines should be no less than four in the azimuthal distribution to obtain acceptable uniformity of the magnetic field.To make the ratio of the current loss to the total current of the accelerator less than 2%at peak anode current,the ratio of the current in each feed line to the total current should be no less than 8%.

Penalty-Finite Element Analysis of the Eddy Current Loss in a Fully-Stabilized Multifilamentary Superconducting Wire

The paper is mainly concerned with the penalty incurred in finite element analysis of the eddy-current loss problem in a fully established multi-filamentary superconducting wire. A finite element model with 4-node quadrilateral isoparametric elements is formulated for the present problem. Unlike the conventional vector potential scheme in use for electromagnetic field problem, the present work features a direct computational approach to eddy current loss. Simplicity and remarkable enhancement in computational accuracy can be obtained with the proposed method.

Calculation of Eddy Current Loss and Short-circuit Force in SSZ11-50000/110 Power Transformer

The ?method is used in this paper to calculate the leakage magnetic field of SSZ11-50000/110 Power transformer, and by which the structures’ influences to the main leakage flux are analyzed. Through the combination of the product and TEAM Problem 21B, the surface impedance method shows its great advantage in the calculation of eddy current loss.

Eddy current loss analysis and frequency optimization design of double-sided LCC-IPT system in seawater environment

Inductive power transfer system can generate eddy current when operating in seawater medium. On the one hand, it can cause eddy current loss, and reduce operating efficiency of the system. On the other hand, it can change parameters of the system and increase difficulty of system design. To grasp the influence mechanism of seawater on the inductive power transfer system,firstly, an equivalent circuit model of double-sided inductor-capacitor-capacitor(LCC) inductive power transfer system in seawater environment was established based on loosely-coupled transformer model of eddy current. Then, based on Maxwell’s equations, the distribution function of the magnetic field and electric current density along radium direction of the coupling coils in seawater medium was obtained by analytical calculation. Besides, in combination with Biot-Savart law, expression of the eddy current loss in transfer direction was derived, and based on which expression of the equivalent of the eddy current loss on the coupling coils was got. Thus the equivalent resistance of the eddy current on the coupling coils in a seawater environment could be predicated, and the optimal operating frequency of the inductive power transfer system could be further optimized. Finally, a prototype of inductive power transfer system was established, which gave the experimental results, and verified the correctness of theoretical analysis, and the experiments showed that: in air medium, the transfer distance was 100 mm, the transfer power was 3.3 k W, and the transfer efficiency was 92.6%;while, in seawater medium, the transfer efficiency was 87%. Eddy current losses mainly caused the reduction in efficiency, and the experimental results of eddy current loss were consistent with the simulation results.

A Review of Medium Voltage Single-Core Cable Armouring, Induced Currents and Losses

Insulated underground cables have the potential to reduce power outages, maintenance costs, and transmission losses compared to overhead lines. On the other hand, they are exposed to several risks and physical damages, since they are buried in the ground. Though the cables are armoured in order to provide mechanical protection and achieve tensile strength, and also to provide effective conductance of earth fault currents. The main purpose of this paper is to introduce insulated underground cables, armouring process, and to analyze the induced currents in metallic parts such as sheath and armour that causeohmic losses which are categorized mainly in two groups as circulating current and eddy current. This paper presents a review on analytical techniques used to analyze the effect of magnetic fields, andcalculate the losses in the armour of the cables, besides providing the strategies and solutions used for armour loss reduction.

三电平辅助变流器寿命优化控制

辅助变流系统是动车组车辆上关键的电气组成部分,主要为空调机组、风机、照明等交流负载提供稳定的三相电源。结温是影响动车组三电平辅助变流器IGBT(Insulated-gate Bipolar Transistor)模块寿命的主要因素。为了提高动车组三电平中点钳位(Neutral-Point Clamped,NPC)型辅助变流器寿命,提出一种降低结温的模型预测电流控制(Model Predictive Current Control,MPCC)策略。首先,考虑传统MPCC在每个采样周期需要代入27个电压矢量循环计算,计算量较大,因此将三电平基本电压矢量划分在间隔60°的6个扇区中,通过计算电压矢量在两相静止坐标下的相角,进而判断参考电压矢量所处扇区,将备选矢量数目从27缩减至10,减少了计算量;其次,传统MPCC直接应用于动车组辅助变流器会使IGBT模块的结温较高,老化速度加快,对变流器安全稳定运行产生不可预测的损害,本文对IGBT模块的开关损耗和导通损耗进行近似等效,得到了和集射极电压、集电极电流相关的功率损耗因子。通过预测每相电流的方向,进而预测IGBT模块的开关和导通情况,动态加入功率损耗因子,并在代价函数中约束每相IGBT及其续流二极管(Free Wheeling Diode,FWD)的功率损耗,使得最优电压矢量在降低功率损耗的同时保证一定的控制性能。通过仿真与实验验证,本文所提方法相比传统MPCC策略降低了功率器件的结温,提高了变流器寿命。

核电半速汽轮发电机励磁绕组匝间短路时转子涡流损耗研究

为研究核电半速汽轮发电机励磁绕组匝间短路时转子涡流损耗特性,推导了核电半速汽轮发电机空载运行时励磁绕组匝间短路故障下,定子分数次谐波环流产生的合成磁动势表达式,分析合成磁动势相对于转子的转速,揭示了转子表面产生涡流的原因以及涡流的频率特性。结合涡流损耗计算方法,以一台核电半速汽轮发电机为例进行了仿真验证。在此基础上,对核电半速汽轮发电机励磁绕组不同位置发生相同程度匝间短路,以及励磁绕组发生不同程度匝间短路过程进行了仿真,计算了转子各阻尼条及槽楔中的涡流及涡流损耗,揭示了励磁绕组匝间短路时影响转子阻尼条及槽楔中涡流和涡流损耗的因素。为核电半速汽轮发电机励磁绕组匝间短路故障时,分析转子发热的影响因素提供了理论基础。

超磁致伸缩力传感执行器磁路优化设计与分析

以超磁致伸缩力传感执行器为研究对象,基于磁致伸缩与涡流损耗理论,应用COMSOL有限元软件进行磁场分析,系统地研究了导磁体参数对磁通密度与涡流的影响规律。为增大磁通密度、减小涡流损耗,以超磁致伸缩棒中轴线上磁通密度均匀度为评价标准,优化了导磁体参数,并将导磁体分区绝缘。静、动态磁场下与未优化时实验结果进行对比,结果表明:静磁场中优化后的磁通密度均值提升了0.0161T,均匀度提升了4.5%;动态磁场中,分区绝缘可有效减少涡流损耗,优化后的力传感器灵敏度提升了5.76%。

混合级联特高压直流功率损失计算方法研究

混合级联特高压直流(UHVDC)在降低直流换相失败风险的同时提升了直流输电的灵活性,但由于LCC与VSC混合拓扑导致不同阀组闭锁后健全阀组的功率传输能力存在不确定性,影响了直流功率损失准确计算。此处提出了一种适用于混合级联UHVDC的功率损失计算方法。直流控制系统以极为单位计算阀组闭锁后的直流功率并发送安控系统计算直流功率损失,设计了合理接口与数据处理方式保证阀组单次及相继故障直流功率损失计算的准确性。最后通过试验,验证了所提方法的正确性与有效性。

基于自抗扰的永磁同步电机附加谐波损耗抑制方法

针对永磁同步电机在变频器供电时,由时间电流谐波所引起的附加谐波损耗过大及难以在电机初始设计时被考虑到的问题,采用场路耦合联合仿真模型来计算电机的附加谐波损耗,并以4台现有的表贴式永磁同步电机为例,通过实验验证了场路耦合联合仿真模型的有效性,为电机设计之初附加谐波损耗的选取,以及后续温升的计算提供了前期计算的方法。同时提出一种基于自抗扰技术的附加谐波损耗抑制方法,设计一种适用于永磁同步电机矢量控制的自抗扰控制器,并从理论上验证了自抗扰控制器对于时间电流谐波的抑制作用,以及针对自抗扰控制器参数众多调参困难的问题,给出一种参数整定方案。最后通过引入所设计的自抗扰控制器,对电机的时间电流谐波进行计算和分析,使电机的附加谐波损耗降低了68.1%,为同类型电机的附加谐波损耗抑制提供了一种有效的方法。

极低频电流场透地通信路径损耗建模与分析

针对水平方向地电极电流场无线强穿透信息传输需求,研究了基于极低频水平双电极电流场信道传输特性。考虑到电极半径、电极入土深度、电极间距、发射信号频率和信号传输距离等参数对透地(Through-The-Earth,TTE)通信传输性能的影响,建立了地电极电流场TTE通信路径损耗模型,分析了各参数对路径损耗的影响,确定了信号传输最佳工作参数。根据选定参数搭建了极低频电流场TTE通信系统,在200 m和400 m通信距离下测试了3~10 Hz信号的路径损耗,通过试验数据与仿真结果对比分析验证了模型的准确性。

高速永磁电机铁耗精确计算两项式模型

基于分段带补偿项的铁耗计算方法,本文提出了一种适用于高速永磁电机铁耗精确计算的两项式数学模型。通过结合高速电机运行特性对频率和磁密区间进行双重划分,在Jordan损耗分离模型的基础上引入涡流及磁滞损耗补偿项考虑磁饱和、局部磁滞回环及涡流趋肤效应等非线性因素对硅钢片单位损耗特性的影响。该模型新增参数均为随频率和磁密变化的分段常函数,通过L-M算法拟合求解,在减小计算量的同时明确反映铁磁材料非线性对铁耗计算的影响,实现铁耗精确计算。最后,以某高速电机用硅钢片35SWH1900为例,对比了本文所提模型与Jordan损耗分离模型在单位损耗上的计算误差,实验结果表明所提模型计算误差基本在15%以内,能够有效提升高速永磁电机铁耗的计算精度。

汽轮发电机转子匝间短路对定子热响应特性的影响

本文分析了汽轮发电机转子匝间短路故障前后定子热响应特性,不仅考虑转子匝间短路引起电压下降对发电机强励动作的影响,还研究了热分布不平衡而引起的定子力学响应。首先推导了正常情况和转子匝间短路故障后加强励磁电流下的气隙磁通密度,得到了铁心损耗和绕组铜耗的解析表达式;然后建立了发电机故障前后的三维有限元仿真模型,对不同短路程度故障下的铁心损耗、绕组铜耗与定子温度进行了求解计算;最后实测了CS-5型故障模拟发电机在正常运行和不同短路程度故障下的定子温度,实验结果与理论分析、有限元仿真结果基本一致。结果表明,转子匝间短路故障后由于励磁电流的增强,发电机铁心损耗和绕组铜耗均会增加,定子温度明显上升,并且随着短路程度的增加而加剧;定子端面边缘位置的变形和应力幅值最大并且为热响应下的危险位置。