Research on Nanosecond Pulse Corona Discharge with Cross Magnetic Field Applied

An application of magnetic field to the nanosecond pulse corona discharge is investigated. A cylinder reactor with different corona electrodes is set up for experimental study. A magnetic field with its direction perpendicular to the corona discharge is applied. Different discharge images are taken under single nanosecond pulse with a high sensitive UV-visible light imagine recorder. Experimental results show that with a cross magnetic field the nanosecond corona discharge both generates paths and develops homogeneously in space more than that without the magnetic field. The results may lead to a possibility to apply a cross magnetic field on nanosecond pulse corona discharge for getting higher desulfurization efficiency.

Coronal Flux Rope Equilibria in Closed Magnetic Fields

Using a 2.5-dimensional ideal MHD model in Cartesian coordinates, weinvestigate the equilibrium properties of coronal magnetic flux ropes in background magnetic fieldsthat are completely closed. The background fields are produced by a dipole, a quadrupole, and anoctapole, respectively, located below the photosphere at the same depth. A magnetic flux rope isthen launched from below the photosphere, and its magnetic properties, i.e., the annular magneticflux Φ_p and the axial magnetic flux Φ_z, are controlled by a single emergence parameter. Thewhole system eventually evolves into equilibrium, and the resultant flux rope is characterized bythree geometrical parameters: the height of the rope axis, the half-width of the rope, and thelength of the vertical current sheet below the rope. It is found that the geometrical parametersincrease monotonically and continuously with increasing Φ_p and Φ_z: no catastrophe occurs.Moreover, there exists a steep segment in the profiles of the geometrical parameters versus eitherΦ_p or Φ_z, and the faster the background field decays with height, the larger both the gradientand the growth amplitude within the steep segment will be.

Time Evolution of the Turnover Frequency for Diagnosis of the Coronal Magnetic Field

Two impulsive microwave bursts observed by Owens-Valley Solar Arrays （OVSA） are studied. The fast time variation of the turnover frequency in these bursts is quite different from the constant value in the earlier conclusion. The observational turnover frequencies are consistent with the calculations using the non-thermal gyrosynchrotron radiation model. We find the turnover frequency may play an important role for calculating the coronal magnetic field on the basis of Dulk and Marsh＇s approximations.

Preprocessing photospheric vector magnetograms for nonlinear force-free field extrapolation of the global corona

Nonlinear force-free magnetic field （NLFFF） extrapolation based on the observed photo- spheric magnetic field is the most important method to obtain the coronal magnetic field nowadays. However, raw photospheric magnetograms contain magnetic forces and small-scale noises, and fail to be consistent with the force-free assumption of NLFFF models. The procedure for removing the forces and noises in observed data is called preprocessing. In this paper, we extend the preprocessing code of Jiang ＆ Feng to spherical coordinates for a full sphere. We first smooth the observed data with Gaussian smoothing, and then split the smoothed magnetic field into a potential field and a non-potential field. The potential part is computed by a numerical potential field model, and the non-potential part is prepro- cessed using an optimization method to minimize the magnetic forces and magnetic torques. Applying the code to synoptic charts of the vector magnetic field from SDO/HMI, we find it can effectively reduce the noises and forces, and improve the quality of data for a better input which will be used for NLFFF extrapolations applied to the global corona.

Measurement of surface charges on the dielectric film based on field mills under the HVDC corona wire

The ion flow field on the ground is one of the significant parameters used to evaluate the electromagnetic environment of high voltage direct current（HVDC） power lines.HVDC lines may cross the greenhouses due to the restricted transmission corridors.Under the condition of ion flow field,the dielectric films on the greenhouses will be charged,and the electric fields in the greenhouses may exceed the limit value.Field mills are widely used to measure the groundlevel direct current electric fields under the HVDC power lines.In this paper,the charge inversion method is applied to calculate the surface charges on the dielectric film according to the measured ground-level electric fields.The advantages of hiding the field mill probes in the ground are studied.The charge inversion algorithm is optimized in order to decrease the impact of measurement errors.Based on the experimental results,the surface charge distribution on a piece of quadrate dielectric film under a HVDC corona wire is studied.The enhanced effect of dielectric film on ground-level electric field is obviously weakened with the increase of film height.Compared with the total electric field strengths,the normal components of film-free electric fields at the corresponding film-placed positions have a higher effect on surface charge accumulation.

Testing a solar coronal magnetic field extrapolation code with the Titov–Dmoulin magnetic flux rope model

In the solar corona, the magnetic flux rope is believed to be a fundamental structure that accounts for magnetic free energy storage and solar eruptions. Up to the present, the extrapolation of the magnetic field from boundary data has been the primary way to obtain fully three-dimensional magnetic information about the corona. As a result, the ability to reliably recover the coronal magnetic flux rope is important for coronal field extrapolation. In this paper, our coronal field extrapolation code is examined with an analytical magnetic flux rope model proposed by Titov ＆ D6moulin, which consists of a bipolar magnetic configuration holding a semi-circular line-tied flux rope in force-free equilibrium. By only using the vector field at the bottom boundary as input, we test our code with the model in a representative range of parameter space and find that the model field can be reconstructed with high accuracy. In particular, the magnetic topological interfaces formed between the flux rope and the surrounding arcade, i.e., the ＂hyperbolic flux tube＂ and ＂bald patch separatrix surface,＂ are also reliably reproduced. By this test, we demonstrate that our CESE-MHD-NLFFF code can be applied to recovering the magnetic flux rope in the solar corona as long as the vector magnetogram satisfies the force-free constraints.

双区与单区电除尘器内部流场电场对比研究

电除尘器内部电场和流场特性对除尘器的除尘性能有重要影响。该文使用Fluent模拟软件对相同比尘集面积的单区与双区电除尘器进行数值模拟,对比单区和双区电除尘器的电场强度、电流密度分布和不同电场风速下的内部流场变化,以此分析电除尘器对不同粒径颗粒除尘效率的影响和双区电除尘器能够高效率捕集高比电阻粉尘的原因。结果表明,双区电除尘器荷电区电流密度与电场强度和单区电除尘器分布相似,单区电除尘器的平均板电流密度为0.56 mA/m^(2),平均电场强度为2.20 kV/cm,双区电除尘器荷电区的平均板电流密度为0.51 mA/m^(2),平均电场强度为2.40 kV/cm。但双区电除尘器收尘区的电场与流场特性和单区电除尘器差别较大,双区电除尘器收尘区平均板电流密度为0.0036 mA/m^(2),只为单区电除尘器的0.6%,而平均电场强度为4.0 kV/cm,是单区电除尘器场强的1.8倍,且双区电除尘收尘区流场分布较均匀,受离子风影响小。收尘区内低电流密度,高电场强度,较少的离子风扰动是双区电除尘器有效捕集高比电阻粉尘,避免反电晕发生的主要原因。

微尺度下场致发射对电晕放电的影响机理

场致离子化微电晕器件基于一维纳米材料的电场增强效应,可产生大气压非平衡微等离子体,适用于气体检测以及生物医疗等领域,具有响应快、低功耗等特点。但微尺度下的电晕放电属于局部自持的低能放电,其场致发射的作用及影响机制尚不清晰。因此文章基于流体-化学混合模型框架,融合F-N发射模型,建立了常温常压N2-O2混合气体的二维微电晕放电模型。通过与无场致发射放电模型对比,探索不同间距下场致发射对放电动态过程的影响,发现针-板间距减至15μm时,两种模型放电过程差异很小,表明放电以二次电子发射机制为主导,当间距减至10μm时,两种模型的放电强度相差近1倍,场致发射的作用及影响不可忽略;通过进一步对电子密度分布、空间电场分布、电流密度等参量进行动态分析,发现场致发射、空间碰撞电离反应和离子轰击二次电子发射之间存在链锁影响规律。

离子风作用下液滴的振荡蒸发特性

设计搭建了离子风作用下液滴蒸发试验装置,研究了不同电场和环境气体中去离子水液滴的蒸发速率、振幅和振荡频率等动态蒸发行为参数,并测量了离子风的流场速度分布.结果表明:当电压低于起晕电压时,电场力会降低液滴蒸发速率;当电压高于起晕电压时,离子风的形成会强化液滴蒸发;电压和气体离子迁移率的增加均会提高离子风的风速,加剧液滴振荡,提高液滴蒸发速率;相比液滴自然蒸发,离子风作用下液滴蒸发速率的最大增强比可达9.89;随着电压增大,离子风从不稳定状态转变为稳定状态.

高压电场选育高产酸性木聚糖酶菌株的研究

为获得适用于动物饲料的木聚糖酶高产菌株,并验证高压电场诱变方法的有效性,于农田土壤中筛选出高产菌株,在高压电场中进行诱变,筛选最佳的突变菌株。出发菌株初步鉴定为沙福芽孢杆菌,命名为Bacillus safensis B16。该菌株所产木聚糖酶在pH 5、60℃下酶活性为217.34 U/mL,且60℃时的半衰期为229 min,热稳定性良好。在6~24 kV、极间距为3 cm的高压电晕电场中处理0~10 min,最终在10 kV下处理6 min选育出一株木聚糖酶高产菌株B16106-2,酶活性达到256.73 U/mL,较出发菌株提升了18.12%,且传代7次后菌株的产酶能力基本不变,具有良好的遗传稳定性。突变菌株所产木聚糖酶的最适酶反应条件不变。研究证明,高压电晕电场是一种有效的诱变方式,且筛选出的菌株B16106-2性能良好。

高海拔特高压变压器均压环结构设计

特高压变压器在投运前需要进行严格的交接试验以保证其能安全可靠运行,而变压器上均压环的均压能力会影响交接试验的准确性。高海拔环境下均压环结构出现问题时其均压能力会发生变化,因此研究设计面对不同状况都能有良好均压能力的均压环尤为重要。文中首先采用COMSOL软件搭建了500 kV变压器耐压试验回路三维模型;其次研究均压环的管径、环径和环间距变化对均压环均压能力的影响;最后研究均压环在毛糙状态下的均压能力变化。研究发现在均压环管径和环径增大或环间距减小时,均压环均压能力会增强,其中管径改变带来的影响最大;均压环为毛糙表面时其均压能力会显著下降,其中粘附圆锥颗粒时均压能力下降最显著,凹陷时下降最少,说明均压环表面越平整,均压能力越好。该研究能为高海拔特高压变压器均压环设计相关工作提供一定帮助。

Simulating gamma-ray production from cosmic rays interacting with the solar atmosphere in the presence of coronal magnetic fields

Cosmic rays can interact with the solar atmosphere and produce a slew of secondary messengers,making the Sun a bright gamma-ray source in the sky.Detailed observations with Fermi-LAT have shown that these interactions must be strongly affected by solar magnetic fields in order to produce a wide range of observational features,such as a high flux and hard spectrum.However,the detailed mechanisms behind these features are still a mystery.In this study,we tackle this problem by performing particle-interaction simulations in the solar atmosphere in the presence of coronal magnetic fields using the potential field source surface(PFSS)model.We find that low-energy(~GeV)gamma-ray production is significantly enhanced by the coronal magnetic fields,but the enhancement decreases rapidly with energy.The enhancement directly correlates with the production of gamma rays with large deviation angles relative to the input cosmic-ray direction.We conclude that coronal magnetic fields are essential for correctly modeling solar disk gamma rays below 10 GeV,but above that,the effect of coronal magnetic fields diminishes.Other magnetic field structures are needed to explain the high-energy disk emission.

高压电晕电场诱变野生草原黑蘑原生质体的初步研究

为提高草原黑蘑菌丝体生长速度,采用高压电晕电场诱变技术处理草原黑蘑原生质体,通过设置4、5、6、7 kV的电压,分别进行30、60、90、120、150、180、210、240、270 s的处理,统计致死率,结合拮抗试验,初步筛选快速生长的新型突变菌株。结果显示,电压为6、7 kV时致死率均为100%,电压为4、5 kV时可获得原生质体再生菌落,致死率为8.45%~81.69%,其中4 kV处理150 s时致死率最高,为81.69%,是获得突变菌株的最佳致死条件;通过再生菌落的形态观察及拮抗试验,获得14株突变菌株,经生长量及生长速率的测量,发现诱变菌株生长后期4 kV的电压较5 kV更有利于促进菌丝体的生长量,在4 kV和5 kV处理条件下获得了生长速度较CK提高的11株正向突变菌株。高压电晕电场诱变技术可为草原黑蘑菌种的新品种选育提供参考。

高海拔地区18 kV水轮发电机定子绕组端部防晕技术研究

为满足海拔高度为2 500 m的某大型水电站18 kV水轮发电机的防晕要求,本文从理论方面分析了目标海拔高度下的空气击穿场强及影响因素,并通过建立定子绕组端部三维仿真模型评估了端部电场特性,分析了间隙距离与绑扎结构对端部斜边电场的影响,确定了定子绕组端部斜边最小间隙距离控制在15 mm的方案。最后,在构建的大型高海拔环境模拟试验室完成了18 kV水轮发电机定子线圈和绕组的防晕性能进行测试验证。结果表明:该18 kV水轮发电机的防晕性能良好,满足在2 500 m海拔高度下的防晕要求。

用于变频电机绝缘测试的高频高压脉冲发生器设计

高频高压脉冲是变频电机绝缘评估的关键技术之一,其产生、控制、保护与传统高压直流、正弦条件下的相应技术具有较大差异,已成为高频高压脉冲技术的关键难题。为此,采用时钟可达纳秒级的现场可编程逻辑门阵列,研制了一套边沿时间40~500 ns可调的高频高压脉冲发生器。基于半桥结构的脉冲发生器,提出测试容量达1600 pF、电压峰峰值可达24 kV的全桥拓扑结构。通过设计多级电压突降保护算法、电流脉宽实时检测、纳秒级脉冲控制技术以及多种抗干扰措施,保障了脉冲发生器在高频电磁干扰环境下安全稳定运行。实验结果表明,该脉冲发生器产生电压的脉宽和死区时间最小1μs,最大重复频率100 kHz,为变频电机全参数绝缘测试提供了新平台。

基于带电颗粒动态积污的绝缘子电场分布研究

为了研究带电污秽颗粒对绝缘子表面积污、电场分布的影响及空气域电晕放电现象,以FXBW-35/70绝缘子为研究对象,采用多物理场耦合有限元软件Comsol Multiphysics搭建了AC-DC、湍流、带电颗粒相互作用及颗粒运动的耦合风洞模型,进行了带电颗粒对绝缘子表面积污、电场和空气域电晕放电分布研究。结果表明:风速越大,迎风区积污速度快于其他区面;粒径增大时,迎风面积污严重,背风区积污很小,侧风区基本无变化;染污中迎风区伞裙表面的电位和电场畸变最为严重,背风区次之,染污后伞裙表面电位、电场有所缓和,迎风区较背风区严重;染污中,靠近高压端和低压端的一大一小伞裙周围空气域存在电晕放电风险,且在靠近高、低压端第一片大伞裙会发生电晕放电;染污后,靠近低压端的大伞裙根部1 mm范围、靠近高压端的整个大伞裙周围和小伞裙根部存在电晕放电风险。

电晕老化对纳米复合PI薄膜介电性能的影响

高温超导非晶合金变压器作为低温运行设备具有节能降耗的功能。选择耐低温的聚酰亚胺(PI)薄膜为高温超导非晶合金变压器主绝缘材料,改进PI薄膜的制备工艺,搭建电晕老化系统,对PI薄膜进行电晕老化预处理。对经电晕老化预处理后的薄膜的介电特性进行研究,发现液氮环境中电晕老化薄膜的介质损耗角正切值要低于常温环境,在质量分数小于或等于5%时纳米粒子填充PI薄膜的介质损耗角正切值小于处理前薄膜的质损耗角正切值。

基于FACE软件和半经验公式分析输电线路的电磁环境

近年来,存在电力系统无法匹配电力复杂电磁环境,挂网运行后可靠性低,影响电力系统稳定运行。因此电力行业对电磁兼容特点进行了更为广泛的研究与测试工作,以便解决电磁骚扰等问题。本文综述了在分析输电线路电磁环境方面所做的一些研究。利用FACE软件可以研究电场和电晕效应这一方面以及经验公式,对我国GIS电场输电线路的电磁环境进行全面的评估。不仅考虑了电场的分布和强度,还对可听噪声、电晕损耗以及无线电干扰等方面进行了量化评估。

Impact of Ion Current on Total Electric Field Measurement Under HVDC Transmission Line

The total electric field(TEF) at ground level induced by high-voltage direct current(HVDC) overhead transmission lines is one of the important indexes for evaluating the lines' electromagnetic environment.Based on analyzing the existing TEF sensors and the measurement principle of ion-current density,the influence from ions on TEF measurements is quantitively studied.The results show that the ions generated by the corona from a HVDC transmission line in operation cause errors in the measurement of TEF.This error is determined through analyzing the component of total measuring current on the filed mill's sensing electrode: if no appropriate approach taken,the maximum measurement error reaches up to 4.3%.Furthermore,a method that can eliminate such error,and hence improve the accuracy of TEF sensors is designed.

Humidity effects on the ground-level resultant electric field of positive DC conductors

The effects of humidity on the ground-level resultant electric field around positive DC conductors were studied both experimentally and numerically. Experiments were carried out in an artificial climate chamber, the results of which showed that the photon count and the groundlevel resultant electric field strength both increased with increasing relative humidity. Numerical calculations for different values of relative humidity were carried out, including solutions of the positive corona inception voltage and the ion-flow field, for which a photoionization model and the upstream finite element method were employed, respectively. In order to analyze the effects of humidity, three main factors were considered: the ionization coefficient, the attachment coefficient in the photoionization model and the modified ion mobility of the charged water particles. The results indicated that, with increasing relative humidity, increasing values of the effective ionization coefficient were responsible for a reduction in the inception voltage, and the reduction reinforced the ground-level resultant electric field. Moreover, due to the charged water particles and the lower ion mobility with increasing relative humidity, the space charge density distribution was enhanced, which also strengthened the ground-level resultant electric field.