Association between Childhood Leukaemia and Exposure to Power-frequency Magnetic Fields in Middle Europe

Abstract Objective Higher levels of exposure to extremely low-frequency magnetic fields （ELF-MF） are associated with a slightly increased risk of childhood leukaemia. Compared with more-developed Western countries, higher exposure levels are evident in the Czech Republic, probably because of the different types of housing. In light of this, we aimed to examine the association between ELF-MF exposure and childhood leukaemia in the Czech Republic. Methods We conducted a paired case-control study. The cases （children with leukaemia） were age- sex- and permanent residence-matched to controls （children without leukaemia）. Although this limited potential bias and confounding, it also limited our number of participants. Results The matched analyses included 79 case-control pairs. No significant association between ELF-MF exposure and childhood leukaemia was observed for exposures over 0.2 μT （odds ratio [0R]=0.93, confidence interval [Cl]=0.45-1.93）, 0.3 μT （0R=0.77, Cl=0.34-1.75）, or 0.4 μT （OR=0.9, Cl=0.37-2.22）. Conclusion Despite higher levels of exposure in Middle and Eastern Europe, no indication of an association between ELF-MF exposure and childhood leukaemia was determined. This in contrast to the findings of previous studies conducted in different countries.

Three-Dimensional Study of the Effect of the Angle of Incidence of a Magnetic Field on the Electrical Power and Conversion Efficiency of a Polycrystalline Silicon Solar Cell under Multispectral Illumination

A three-dimensional approach to the effect of magnetic field incidence angle on electrical power and conversion efficiency is performed on a front-illuminated polycrystalline silicon bifacial solar cell. A solution of the continuity equation allowed us to present the equations of photocurrent density, photovoltage and electric power. The influence of the angle of incidence of the magnetic field on the photocurrent density, the photovoltage and the electric power has been studied. The curves of electrical power versus dynamic junction velocity were used to extract the values of maximum electrical power and dynamic junction velocity and to calculate those of conversion efficiency. From this study, it is found that the conversion efficiency values increase with the angle of incidence of the magnetic field.

Analysis of temperature field for a surface-mounted and interior permanent magnet synchronous motor adopting magnetic-thermal coupling method

Aiming at obtaining high power density of surface-mounted and interior permanent magnet synchronous motor(SIPMSM),it is important to accurately calculate the temperature field distribution of SIPMSM,and a magnetic-thermal coupling method is proposed.The magnetic-thermal coupling mechanism is analyzed.The thermal network model and finite element model are built by this method,respectively.The effects of power frequency on iron losses and temperature fields are analyzed by the magnetic-thermal coupling finite element model under the condition of rated load,and the relationship between the load and temperature field is researched under the condition of the synchronous speed.In addition,the equivalent thermal network model is used to verify the magnetic-thermal coupling method.Then the temperatures of various nodes are obtained.The results show that there are advantages in both computational efficiency and accuracy for the proposed coupling method,which can be applied to other permanent magnet motors with complex structures.

Electromagnetic Environmental Impact of 500-kV Double -Circuit Transmission Lines

The strength of the power frequency electric intensity and magnetic field of the 500-kV double circuit transmission lines was calculated by using the equivalent charge method and the Ampere's Law, and the environmental impact factors of the fields were evaluated. By optimizing the phase sequence, the frequency electric intensity and magnetic field strength can be reduced. Within a distance of 25 m from the center of the transmission line, the power frequency electric intensity and magnetic field strength fall off sharply with the distance increase. Finally, the best phase sequence and the minimum ground clearance of the transmission lines were obtained to meet the requirements of the least impact on envionment.

An Analysis of Magnetic Field Environment Near High-Voltage Power Lines and Contact Wires of Electric Railways

Image method is used in this paper to calculate the value of magnetic field near high-voltage transmission lines and electric railways. Areas in which the magnetic field is less than 0.002 Gauss are given and the magnetic pollution of high-voltage power transmission lines and electric railways is discussed

Theory of Electromagnetism and Gravity —Modeling Earth as a Rotating Solenoid Coil

Presented in this manuscript are conventional electrical engineering tools to model the earth as a rotating electrical machine. Calculations using known parameters of the earth and measured field data has resulted in new understanding of the earth’s electrical system and gyroscopic rotation. The material makeup of the inner earth is better understood based on derived permeability and permittivity constants. The planet has been modeled as simple coils and then as a parallel impedance circuit which has led to fundamental insight into planetary speed control and RLC combination for Schumann Resonance of 7.83 Hz. Torque and Voltage Constants and the inverse Speed Constant are calculated using three methods and all compare favorably with Newton’s Gravitational Constant. A helical resonator is referenced and Schumann’s Resonant ideal frequency is calculated and compared with others idealism. A new theory of gravity based on particle velocity selector at the poles is postulated. Two equations are presented as the needed links between Faraday’s electromagnetism and Newtonian physics. Acceleration and Deceleration of earth is explained as a centripetal governor. A new equation for planetary attraction and the attraction of atomic matter is theorized. Rotation of the earth’s electrical coil is explained in terms of the Richardson effect. Electric power transfer from the sun to the planets is proposed via Flux Transfer Events. The impact of this evolving science of electromagnetic modeling of planets will be magnified as the theory is proven, and found to be useful for future generations of engineers and scientists who seek to discover our world and other planets.

基于频率切换实现恒流/恒压输出的电场耦合无线电能传输系统

电场耦合无线电能传输(electric-field coupled wireless power transfer,EC-WPT)技术的实际应用中,有些用电设备需要系统具有不同的恒定输出特性(恒流/恒压),即系统输出电压或输出电流与负载解耦,此外,系统还需具备在恒流、恒压模式间按需切换的功能。针对该需求,基于LC-CLC谐振网络提出1种具有恒流/恒压输出特性的EC-WPT系统,分析LC-CLC谐振网络特性,推导恒流/恒压输出特性的实现条件以及恒流频率和恒压频率的计算方法,并给出系统参数设计方法,分析系统对工作频率的敏感性。最后通过仿真和实验验证所提出的EC-WPT系统恒流/恒压输出特性及其参数设计方法的正确性和有效性。实验结果表明所提出的系统在输入电压恒定的不同负载工况下分别实现2 A的恒流输出以及96 V的恒压输出,其最大传输效率分别为87.83%及88.17%。

基于小波变换和压缩感知的工频磁异常信号降噪方法

针对强噪声背景下水下目标微弱工频磁异常信号提取困难的问题,提出一种基于小波变换的压缩感知降噪方法。该方法利用噪声信号不具有稀疏性的特点,将含噪信号在小波域内分解,并在此基础上进行压缩感知的重构与降噪处理,实现微弱工频磁异常信号与噪声最大限度地分离。仿真及试验表明,该方法得到很好的降噪效果,避免了小波阈值滤波中阈值选取对降噪效果的影响,能够最大程度地保留原始信号的固有特征。

750kV单回并行输电线路电磁辐射环境研究

采用《环境影响评价技术导则输变电》(HJ 24—2020)附录C、D推荐的计算模式对750 kV单回并行输电线路电磁辐射环境进行计算与预测。结果表明,经过耕地、园地、牧草地、畜禽饲养地、道路等场所,当导线对地最小高度为15.5 m时,单回并行线路下的工频电场强度最大值超过10 kV/m;需将导线对地最小高度提至16.5 m,才能满足4 kV/m控制限值要求。750 kV单回并行输电线路产生的工频磁场强度小于公众曝露控制限值(100μT),一般情况下不会成为线路建设的环境制约因素;但其产生的工频电场是电磁环境影响的主要因素,电场强度控制限值(4 kV/m)是线路建设的环境制约因素,同时也是输变电电磁环境重点控制因素。现场实测结果与理论预测结果符合性较好,表明采用的预测模式具有较好的应用性,研究结果可为750 kV单回并行输电线路的建设和环境监管提供支持。

高气压下氮氧混合气体的工频击穿特性

文中通过工频击穿实验研究了不同电场均匀度、配比、气压下氮氧混合气体的工频绝缘特性。实验发现:板—板电极下,配比对氮氧混合气体的击穿电压影响较小,氮氧混合气体的击穿电压随充气压力的提高均呈增长趋势;棒—板电极下氮氧混合气体的击穿电压明显降低;针—板电极下氮氧混合气体的击穿电压在0.6~0.9 MPa出现“驼峰”效应,随着针—板电极间距增大“,驼峰”效应越发显著,较高气压下绝缘强度出现饱和。综合分析表明,在不同电场均匀度下,0.8 MPa时80%N_(2)/20%O_(2)与SF_(6)在0.4 MPa时80%的绝缘强度相当。研究结果可为氮氧混合气体作为绝缘介质的设备设计提供参考,对推动电气设备的低碳绿色发展具有重要意义。

低频交流电压下低密度聚乙烯的空间电荷特性

分频输电技术已逐步成为实现碳中和及海上风电远距离传输的主流方案之一。然而,对高压分频输电背景下的电气设备研究较为欠缺,在频率改变对电缆绝缘材料特性影响方面尚需深入研究。为此,采用具备快速检测能力的脉冲电声测试系统,研究了低密度聚乙烯材料在分频电压下不同电场强度、温度时的空间电荷特性以及频率改变对电荷积聚行为的影响。结果表明:当场强及温度条件较为苛刻时,电荷积聚明显;而随着频率的降低电荷积聚量增加,频率下降至20 Hz后,电荷增长速度显著提高。在此基础上,建立了应用于交变电场下的双极型载流子模型,通过仿真计算对实验观察进行了合理化解释,揭示了电场、温度及频率对空间电荷行为的影响机理。研究方法和结果可为海上风电分频输电系统中的频率选择及线缆绝缘优化设计提供理论支撑。

云南澜沧老厂银铅锌多金属矿床的AMT工频噪声压制研究

云南澜沧老厂银铅锌多金属矿床为西南“三江”地区的典型矿床,面临资源危机。该矿床的边部找矿勘查中开展了音频大地电磁测深(AMT)工作,但因高压线工频干扰,导致部分测点频点失真。针对此问题,提出了一种基于隔离式频点提取以及磁场数据重构技术的工频噪声压制方法。通过划定阈值对所有测点进行数据分辨,进而快速区分受工频干扰程度不同的测点;然后避开受干扰的50 Hz及倍数频段数据进行数据提取。针对受工频干扰程度较强,无法避开干扰数据的测点,利用其临近测点数据,采用反距离加权法对强干扰测点进行磁场数据重构。对澜沧老厂银铅锌多金属矿床的AMT资料采用上述方法进行处理后,有效规避了50 Hz及奇次谐波干扰,取得了较好的噪声压制效果,圈定了2处具有找矿潜力的低阻异常区,为矿山边部找矿勘探提供了方向。该方法为解决物探工作中的工频干扰提供了新途径。

O_(2)体积分数对N_(2)/O_(2)混合气体工频绝缘强度的影响

为了研究不同比例N_(2)/O_(2)混合气体的工频绝缘特性,分析O_(2)占比对混合气体绝缘性能的影响,文中采用Boltamann方程,对比了Wieland近似与Garland近似两种方法,基于电子输运参数计算了不同比例下N_(2)/O_(2)混合气体的临界电场,分析了O_(2)对混合气体绝缘性能的影响;同时开展了0.1~0.8 MPa下5%~21%O_(2)占比的N_(2)/O_(2)混合气体工频放电实验,结合实验数据验证了计算结果的可靠性。文中发现在实验比例范围内,O_(2)占比对N_(2)/O_(2)混合气体工频绝缘特性几乎无影响,气压与N_(2)/O_(2)混合气体的放电电压成线性相关。文章可为以洁净空气电力设备的设计、运维提供参考。

基于频率差的工频磁场抗扰度试验方法

现有工频磁场抗扰度试验方法评价受试设备在工频磁场骚扰下的采样性能时,试验结果随机,可能出现误判。结合GB/T 17626.8-2006要求、试验方法及试验仪器的特点,文章分析了试验结果出现随机现象的原因。在此基础上,提出了基于受试设备基本分量及干扰分量频率差的工频磁场抗扰度试验方法。多种电气二次设备的工频磁场抗扰度试验结果表明,频率差法通过人为合理设置频率差,在受试设备的正常使用状态下,可有效检测出工频磁场骚扰对受试设备的最大影响程度,消除了试验结果的随机性。频率差法适应性好、操作简便,不仅适用于电力工业领域,也有利于形成具有良好的共同性和重复性的基准。

C_(4)F_(7)N-air混合气体在稍不均匀和极不均匀电场中的工频绝缘特性分析

近年来,作为SF_(6)有效替代气体之一,七氟异丁腈(C_(4)F_(7)N)因其优异的电气性能和物化特性而受到关注与讨论,然而由于C_(4)F_(7)N的液化温度较高,需要与低液化温度的缓冲气体并用。选择空气作为缓冲气体,在稍不均匀电场与极不均匀电场下,通过工频击穿实验研究气压、混合占比和电极间隙对C_(4)F_(7)N-air混合气体工频击穿电压的影响。结果发现:C_(4)F_(7)N-air混合气体在两个电场下的工频击穿电压随着电极间隙的增大而近似线性增加,在极不均匀电场下,出现明显“驼峰”效应,混合比为8%~16%的C_(4)F_(7)N-air混合气体工频击穿电压可达到同条件下SF_(6)的67%~86%。在稍不均匀电场下,8%C_(4)F_(7)N/92%air混合气体的绝缘强度约为同条件下SF_(6)的0.8倍。混合比为12%~16%的C_(4)F_(7)N-air混合气体具备与SF_(6)相等的工频绝缘强度。总结:与SF_(6)对比,C_(4)F_(7)N占比为8%~16%的C_(4)F_(7)N-air混合气体具备替代SF_(6)气体的潜力。

500kV变电站内敞开式断路器感应电流计算分析

为分析断路器与地线形成的回路中产生感应电流的特性,文章对处于变电站500 kV开关场内的断路器、导线、地网和2个接地线与接地刀闸组成的通流体回路中的感应电流进行测量,并分别对变电站500 kV开关场正常工作状态下和检修状态下的工频磁场进行仿真。研究结果表明:在检修状态下500 kV开关场内断路器通流体回路产生的感应电流峰峰值在3.85~7.33 A之间;正常工作状态下开关场磁感应强度范围在0.260~7.480μT之间,工频磁场强度最大值主要集中分布在导线交叉处;检修状态下开关场磁感应强度范围在0.440~8.760μT之间,工频磁场强度较大值主要集中分布在第2回母线下方。研究结果为敞开式断路器检修人员安全作业提供参考。

基于有限元法和模拟电荷法的高压输电线路工频电场研究

为更好地研究高压输电线路工频电场效应在不同气象条件下的变化规律,运用有限元法和模拟电荷法,结合高压输电线下工频电场相关理论知识,在高压输电线路下,分析车辆对人体的电击效应。首先,对人体的暂态电击电流峰值、暂态放电能量和稳态电击电流进行精确计算。其次,应用有限元法,仿真和分析小型车对人体所产生的暂态电击电流峰值以及暂态放电能量,并比较最终仿真结果。结果表明:理论计算值与仿真分析值之间存在10%左右的误差,当人所处的电场强度为5~10kV/m,且接触小型车时,由于该场强没有超出人体的疼痛阈值,人体仅仅出现触电感觉,不会危及人体生命安全。高压输电线路工频电场场强低于人体疼痛阈值,安全可靠,并不会对人体造成生命危险。该研究成果能够为相关人员提供有益的借鉴和参考。

基于有限元法的串补站电场分布特性研究

串补工程所涉设备繁多,在布置上与常规站有明显差别,其对电站电磁环境有较大影响。采用三维有限元分析计算方法,结合国外某400 kV串补工程,建立三相完整模型,对串补站近地工频电场分布及其影响因素展开研究。通过模型的对比分析表明:设计尺寸下的串补站近地电场分布满足限值要求,单一因素的变化仅对相关设备邻近区域的电场分布有显著影响;在一定范围内,平台及围栏越高,线路距离越近,近地电场分布所受影响越趋积极。

Study on Magnetic Field Distribution in Electromagnetic Ingot Casting Mold for Extra Heavy Plate

The dual-frequency electromagnetic ingot casting(DFEMIC)method with copper water-cooled ingot mold for extra heavy plate was developed.Electromagnetic field distribution in ingot mold was measured through the teslameter,the shielding effect of the copper ingot mold was judged,it is less than 37.7%of magnetic flux density when there is no ingot mold.The average shielding the magnetic field proportion of copper ingot mold reduced to 54.9%after loading '「' type the magnetic yoke and adjusting its distribution.Improving electromagnetic power can increase the magnetic field strength. Using the slit combination ingot mold could help increasing magnetic flux density in ingot mold.Steel structure outside ingot mold also have interference on magnetic field distribution in ingot mold,Therefore,it is important to paid more attention to electromagnetic shielding and the uniform symmetry of system structure.

基于改进卷积神经网络的工频水下磁目标探测

针对工频水下磁目标信号特征提取难、目标数据样本少、识别精度低等问题,提出一种基于深度卷积生成对抗网络(DCGAN)与优化卷积神经网络(CNN)相结合的水下工频磁目标识别方法。该方法通过滑动时间窗将信号由一维时序空间映射到二维灰度值图像,将实测水下磁异常信号利用DCGAN进行数据增强,之后构建卷积神经网络并引入DY-ReLU动态激活函数对CNN网络结构进行优化,以达到对目标信号的分类识别的目的。实验结果表明,经由数据增强的网络模型识别率提高了10%;相较于其他常用的静态激活函数,优化的CNN识别率分别提高了4.5%、4%、3%和2.5%,识别精度达到92.5%。验证了该方法的有效性,为水下磁异常检测提供一种新思路。