Phase field model for electric-thermal coupled discharge breakdown of polyimide nanocomposites under high frequency electrical stress

In contrast to conventional transformers, power electronic transformers, as an integral component of new energy power system, are often subjected to high-frequency and transient electrical stresses, leading to heightened concerns regarding insulation failures. Meanwhile, the underlying mechanism behind discharge breakdown failure and nanofiller enhancement under high-frequency electrical stress remains unclear. An electric-thermal coupled discharge breakdown phase field model was constructed to study the evolution of the breakdown path in polyimide nanocomposite insulation subjected to high-frequency stress. The investigation focused on analyzing the effect of various factors, including frequency, temperature, and nanofiller shape, on the breakdown path of Polyimide(PI) composites. Additionally, it elucidated the enhancement mechanism of nano-modified composite insulation at the mesoscopic scale. The results indicated that with increasing frequency and temperature, the discharge breakdown path demonstrates accelerated development, accompanied by a gradual dominance of Joule heat energy. This enhancement is attributed to the dispersed electric field distribution and the hindering effect of the nanosheets. The research findings offer a theoretical foundation and methodological framework to inform the optimal design and performance management of new insulating materials utilized in high-frequency power equipment.

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.

Improved Method of Power Loss and Electric Field Calculations of HVAC Transmission Lines

An improved method for calculating the corona power loss and the ground-level electric field on HVAC transmission lines induced by corona is proposed.Based on a charge simulation method combined with a method of successive images,the proposed method has the number and location of the simulated charges not arbitrary.When the surface electric field of a conductor exceeds the onset value,charges are emitted from corona into the space around,and the space ions and the surface charges on each sub-conductor are simulated by using the images of the other sub-conductors.The displacements of the space ions are calculated at every time step during corona periods in both the positive and the negative half cycles.Several examples are calculated by using the proposed method,and the calculated electric field at the ground level and the corona power loss agree well with previous measurements.The results show that simulating 12 charges in each conductor during 600 time steps in one cycle takes less time while guarantees the accuracy.The corona discharge from a 220 kV transmission line enhances slightly(less than 2%) the electric field at the ground level,but this effect is little from a 500 kV line.The improved method is a good compromise between the time cost and the accuracy of calculation.

Analysis of impulse electric field effect on organic exhaust gas decomposition

The technique of organic exhaust gas decomposition with impulse corono dischrge plasma has been investigated in this study. It has been discovered that the impulse electric field affected the decomposition efficiency with the secondary electron emission coefficient (δ) of the corona electrode as an intermediary: when the impulse voltage power ( W ) was fixed the corona electrode material with higher δ could induce higher decomposition efficiency. In these experiments, wolfram electrode which has the highest δ has really induced the highest decomposition efficiency.

A Multivariable, Two-Dimensional Plot of Electromagnetic, Electric Field and Seismic Information for the Characterization of Earthquake Precursors

Removal of the electrical shielding from a type of Fourier transform seismometer overlays seismic information with Extremely Low Frequency-range (ELF) electromagnetic signals between about 0.3 Hz and 36 Hz (the ITU-designated range of ELF is 3 to 30 Hz). The observed signals originate in the electric power grid, shown clearly by the fact that they are sum and difference heterodyne products with the power grid’s higher harmonics of 60 Hz, typically the 36th and 37th, because the seismometer’s chosen frequency modulation (FM) carrier frequency is roughly 2200 Hz. It is especially interesting that on 2017-03-19, prior to 14:25:12 UTC, the instrument recorded an 11 minute sequence of 20.3 Hz ELF outbursts that culminated intimately with a 3.2 magnitude earthquake located a few miles west of Bardwell KY. These ~20.3 Hz ELF signals, very near the third Schumann resonance frequency, have been recorded numerous times. They are distinctive and fairly strong, ranging 15 to 30 db or more above the noise floor, but definitely not an every-day event;months can pass without them. So far most of these ELF signals do not have an intimately associated earthquake, with the event of 2017-03-19 being one of only two exceptions recorded thus far. That quake’s location was more than one hundred miles from the instrument, in the New Madrid Seismic Zone (NMSZ). The second case, a quake in Kansas, was about three times farther from the instrument, and its ELF signals were correspondingly weaker. Those other, unassociated electromagnetic events might come from quakes too weak to detect, but it should be noted that stronger, easily detected quakes also rarely exhibit any ELF/seismic “connectivity”. This paper describes an instrument that overlays ELF, electric field and seismic signals. The instrument’s two-dimensional (2D) output has a time axis (horizontal) resolution of ~3 seconds and an ELF frequency (vertical) resolution of ~0.3 Hz.

Air breakdown induced by the microwave with two mutually orthogonal and heterophase electric field components

The air breakdown is easily caused by the high-power microwave, which can have two mutually orthogonal and heterophase electric field components. For this case, the electron momentum conservation equation is employed to deduce the electric field power and effective electric field for heating electrons. Then the formula of the electric field power is introduced into the global model to simulate the air breakdown. The breakdown prediction from the global model agrees well with the experimental data. Simulation results show that the electron temperature is sensitive to the phase difference between the two electron field components, while the latter can affect obviously the growth of the electron density at low electron temperature amplitudes. The ionization of nitrogen and oxygen induces the growth of electron density, and the density loss due to the dissociative attachment and dissociative recombination is obvious only at low electron temperatures.

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.

基于电场耦合的电能信号并行传输系统串扰抑制方法

针对较大功率电场耦合无线电能传输系统信号双向高速传输的需求,该文提出一种基于部分能量通道的电能与信号并行传输系统的串扰抑制方法。通过对所提出的系统拓扑进行分析,给出了电能传输增益表达式与电能串扰增益表达式,并分析了阻波电路参数变化对电能串扰增益的影响;基于交流阻抗法及香农定理分别给出了信号传输增益及信道容量表达式,分析了信号支路参数对信道容量的影响;在综合考虑信号传输增益、信道容量及阻波电路参数敏感性的情况下,给出系统信号支路参数的设计方法。该方法能保证系统在较大功率下降低电能串扰,保障信号稳定传输,实现信号的双向高速传输。通过仿真与实验验证了所提出的拓扑和参数设计方法的有效性。搭建的实验装置实现了传输530.4 W的电能,23.28 Mbit/s信号正向传输速度和24.2428 Mbit/s信号反向传输速度。

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%。

道路地下空洞探地雷达波场和时频特性

根据城市道路地下介质的分布特征和电性参数设计模型,采用时域有限差分法和广义S变换,对道路地下存在的充气空洞、充水空洞、回填不密实、埋藏金属物状态进行探地雷达正演模拟和时频特征提取。结果表明,地下空洞顶界面的反射波同相轴均呈弧形反射形态,但充气空洞的反射波能量强于充水空洞;地下空洞发育区域的中心频率集中在某个低频区间,其余频率成分分布较均匀;埋藏金属物区域出现两簇高幅值能量团,频率分布较分散;回填不密实区域频率未能显示出较明显的规律。最后,通过工程实测验证了数值模拟的可靠性。

基于容性屏蔽的无线电能传输系统有源磁屏蔽结构优化

为了改善无线电能传输系统中的磁场泄漏问题,本文提出了一种基于无源容性屏蔽的强耦合有源磁屏蔽结构。首先,在无源容性屏蔽的无线电能传输系统的基础上,设计了一种强耦合有源磁屏蔽线圈结构。其次,给出了此线圈的工作原理与设计方法,推导了数学模型以及等效电路模型。从理论出发解释了容性屏蔽和有源屏蔽的原理,并对屏蔽效果及传输效率受屏蔽线圈参数变化的影响作了分析。最后,结合得到的线圈参数,在所提线圈结构的基础上,设计出了一套电动汽车无线充电系统,通过理论计算、仿真和实验,对所提线圈结构和方法的有效性进行了验证。结果显示,该线圈结构在维持96%以上传输效率的同时,能够将系统的漏磁减少大约40%,实现了降低泄漏磁场和保持高传输效率的目标。

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。

磁感定义与复磁路相量分析

该文以变压器为例,分别建立并联和串联两种形式的等效正弦交变复磁路模型,相应地给出两种磁感的不同定义和物理意义,并比较各自的优劣势。首先,以相量图的形式分析不同负载性质等效复磁路中各物理量的相位关系,并在磁感定义的基础上完善磁路与电路的类比关系;其次,推导任意负载下等效电路有功和无功功率与类比复磁路中等效电路中虚拟有功和无功功率的数值关系;然后,以同步发电机为例,利用基于磁感的等效复磁路分析交流电机中定转子磁场的相互作用,分别基于等效复磁路和有限元方法分析一个变压器算例,验证理论分析的正确性;最后,给出研究结论,并据此客观地分析基于磁感的复磁路的作用。

信号与能量极板层叠方式下的电场耦合式无线电能传输系统

为了提升共享部分能量通道式的电能与信号并行传输系统在传输极板面积受限的应用场合中的能量传输性能,并实现信号双向高速传输,提出一种信号传输极板与能量传输极板层叠方式下的电场耦合式无线电能传输(electric-field coupled wireless power transfer,EC-WPT)系统,给出系统拓扑及串扰抑制方法。基于交流阻抗分析法及香农第二定理,建立电能串扰增益、信号传输增益、信号最大传输速率及电能传输增益的数学模型,分析交叉耦合电容对电能串扰增益及信号传输的影响;以降低交叉耦合电容对信号传输增益及信号最大传输速率的影响为目标,给出层叠方式下EC-WPT系统信号传输极板面积及信号支路参数的设计方法。仿真与实验验证了所提出的系统及给出的方法能在较大传输功率下实现系统的信号双向高速传输。所搭建的实验装置实现了在系统输出功率达到520.2 W时,信号正向传输速度为18.64 Mbit/s和信号反向传输速度为19.36 Mbit/s。

无线电能传输系统高效率低漏磁的全向环绕型有源磁屏蔽结构

在电动汽车无线电能传输系统(WPT)中,如何通过电磁屏蔽技术来降低WPT系统中的漏磁,同时维持较高的传输效率是一个难题。为此本文提出了一种全向环绕型有源磁屏蔽线圈结构来减少WPT系统中的漏磁。首先,分析了该结构的磁屏蔽工作原理以及设计思路,推导了该结构的数学模型;其次,根据本文线圈结构高效率低漏磁的特点,提出了一种线圈优化方法,得到了满足设计要求的线圈参数;最后,根据得到的线圈参数,搭建了一套基于所提线圈结构的WPT系统,并通过仿真和实验验证了该结构和方法的合理性。结果显示,在传输功率为4 kW时,本文提出的线圈结构在偏移0 cm时,目标面的最大漏磁为3.76μT,相比无屏蔽线圈结构降低了43.63%的漏磁,并且传输效率高达95.58%;在偏移10 cm时目标面的最大漏磁为6.03μT,仍符合漏磁安全标准,并且传输效率为92.92%,高于同尺寸无源屏蔽线圈结构和传统有源屏蔽线圈结构的传输效率。

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。

电场耦合式无线电能传输技术在航天领域应用前景展望

将无线电能传输技术引入航天器的旋转供电中是推动航天器进一步发展的重要手段。而现有应用最广的磁耦合式无线电能传输技术(inductive power transfer,IPT)因成本高、重量大、存在涡流损耗等缺陷而难以在航天领域中得到大规模应用。而电场耦合式无线电能传输技术(capacitive power transfer,CPT)以其成本低、重量轻等优点,近年来受到广泛关注,在航天领域具有巨大潜力。从传统IPT技术在航天领域应用的缺陷入手,分析将CPT技术引入航天领域无线供电场景的重要性。进而介绍了CPT技术的发展历程与基本原理,并对CPT技术在轻量化、大功率、旋转型三个领域的研究现状进行综述来论证其在航天领域应用的潜力。最后总结了CPT技术在航天领域应用存在的问题并分析了解决这些问题可行的技术手段。

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