气压和湿度对复合电压下换流阀高压电极起晕电压影响试验

柔性直流换流阀在运行时,其内部尖端以及钳制电位差较大的相邻屏蔽罩可能由于承受过高的交直流复合电压和局部场强过大而产生电晕放电现象。而气压和湿度因素对起晕电压具有一定的影响。因此根据换流阀内部电极电场的特点设计了换流阀高压电极(棒–板电极和屏蔽罩缩比电极)。采用串联加压的复合加压方式和紫外成像技术,在实验室内搭建了气压和湿度可调的交直流复合电压电晕试验平台。之后基于试验平台研究了气压和湿度对复合电压下换流阀高压电极起晕电压的影响。试验结果表明:随着气压的下降,复合电压下和单一电压下棒–板电极的起晕电压均线性下降;复合电压下屏蔽罩缩比电极起晕电压逐渐下降;单一电压下屏蔽罩缩比电极的起晕电压线性下降。随着相对湿度的增大,正直流–交流复合电压下棒–板电极的起晕电压基本不变;负直流–交流复合电压下棒–板电极的起晕电压逐渐减小;单一电压下棒–板电极的起晕电压均逐渐线性减小。随着相对湿度的增大,正直流–交流复合电压下屏蔽罩缩比电极的起晕电压先减小后增大;负直流–交流复合电压下屏蔽罩缩比电极的起晕电压则逐渐减小;纯正直流电压下,屏蔽罩缩比电极的起晕电压先增大后减小;纯交流和纯负直流电压下,屏蔽罩缩比电极的起晕电压逐渐减小。

高压直流导线表面粗糙度与电晕放电时粗糙系数的关系

高压输电线路表面磨损会对线路电晕放电造成影响。粗糙系数是根据导线表面状态预测起晕场强的重要参数。文中研究了表面粗糙度与高压直流导线起晕场强以及粗糙系数之间的关系,基于触针法测量了圆截面导线的表面粗糙度,利用圆柱电晕笼获得了导线正负极直流起晕电压,得到了粗糙系数与导线表面粗糙度之间的变化规律。导线粗糙度在0.5μm到2.5μm的范围内变化时,粗糙系数随表面粗糙度增大而减小。与正极相比,表面粗糙度对负极电晕放电影响更大。表面粗糙度越大,粗糙度变化对粗糙系数的影响越明显。

交直流复合电压下棒-板电极起晕电压实验分析

为了获得复合电压作用下电极的起晕特性,在室内搭建了复合电压下无锈棒-板电极起晕特性实验平台,采用串联的复合加压方式,即一个电极上施加直流电压,另一个电极上施加交流电压,以紫外光子计数的突变作为电晕起始判据,获得了直流和交流复合电压下的电极起晕特性。同时对比了不同直流电压极性、电极加压方式和不同复合电压升压方式下电极起晕电压的特点,探究复合电压下棒电极半径和棒板间隙对电极起晕电压的影响。实验结果表明:在相同的大气条件及电极布置下,由于空间电荷影响,棒电极正直流、板电极交流加压方式下的起晕电压比棒电极交流、板电极正直流加压方式下的起晕电压高;在棒-板气隙间距0~5cm范围内,定直变交复合升压方式下,交直流分量有效值叠加后的起晕电压随着直流分量的增加而升高,定交变直方式下,该值随着交流分量的增加而下降,且交直流分量间互为线性关系。本文的研究成果可以为进一步研究复合电压作用下电极的电晕机理及起晕电压的准确预测奠定坚实基础。

多导体电容系统多端口表示方法

部分电容是“工程电磁场”课程的一个重要内容,是电气领域经常应用的重要知识。结合微分形式电荷守恒方程和等效电路模型获得了无损耗多导体电容系统部分电荷守恒方程;基于正弦稳态电路结点导纳法得到了用部分电容和支路电压表示的多端口库伏关系;以3+1多导体电容系统为例,讨论了多导体电容系统的部分电容、感应系数矩阵和电位系数矩阵对应元素关系。该教学思路在教学应用中更易被学生理解和接受。

不同极性乙烯-醋酸乙烯酯共聚物对低密度聚乙烯共混体系电性能的影响

低密度聚乙烯(LDPE)具备优良的化学稳定性和电气绝缘性加工性,常常用作高压绝缘电缆材料,但是,LDPE在高压直流电场下的运行过程中也会面临诸多问题,其中最突出的问题是空间电荷在绝缘材料中的积聚行为。针对此,选取2种不同牌号的乙烯醋酸乙烯酯共聚物(EVA),采用熔融共混法改性LDPE基体,通过结晶行为和陷阱特性研究LDPE/EVA共混体系的空间电荷积聚行为和直流击穿强度。结果表明:对比纯LDPE,2种共混物都消除了空间电荷包现象,其中LDPE/EVA 18-150共混物直流击穿强度提高至329 kV/mm;由此说明,添加EVA填料在提高材料的电绝缘性能方面具有潜在的应用价值。

基于脂肪族羧酸酯固化的环氧复合材料的制备及其性能

将3,3'-二硫代二丙酸二甲酯(DTDP)结合传统的甲基四氢邻苯二酸酐固化剂对环氧树脂进行固化,制备了环氧树脂复合材料,利用FTIR、TG、DMA、DSC等方法研究了环氧树脂复合材料的固化反应动力学,分析了固化机理,并考察了力学和电学性能。实验结果表明,添加DTDP后,环氧树脂复合材料交联密度提高,故拉伸强度提高,但同时也提升了韧性,其中,EP-DTDP-2的拉伸强度和断裂伸长率分别达到了81.3 MPa和5.7%,比纯环氧树脂分别提升了16.1%和104%。交联密度的提高还使环氧树脂复合材料的击穿强度有所提升,其中,EP-DTDP-3的击穿强度达到最高(37.6 kV/mm),比纯环氧树脂(33.8 kV/mm)提高了11.2%。

The role of varied metal protrusions on the conductor surfaces in corona discharge subjected to DC high voltages

Conductor corona performance is significant in the evaluation of electromagnetic environment for high voltage power transmission lines. The influence of artificial contaminated conductors on corona discharge was studied and turned out to be complicated. The ionized field strength on the corona cage was measured by field mill. Meanwhile, photos of corona plumes were photographed and grayed to quantitate the corona discharge intensity. Subsequently, a calculation model for equivalent electric field strength coefficient was established to evaluate the discharge intensity of conductors in coaxial cylindrical electrode. It could be found the computational results achieved an agreement with the observed experimental phenomena. By means of simulation results, a reasonable explanation was given to the finding that the closer the distance between the two protrusions was, the lower the corona discharge intensity and higher corona inception voltage of the conductors would be. In summary, the distributions of corona sources played an important role in the corona discharge and this work would provide an important reference for the evaluation of corona effects on the surface of contaminated conductors.

The role of low air pressure in the variation of negative corona-generated space charge in a rod to plane electrode

The corona-generated space charge may vary in different air pressures,and the quantitative law between the corona-generated space charge density and air pressure has never been investigated.This work utilised computational approaches to explore the role of air pressure in the variation of negative corona-generated space charge.A negative fluid model in which the air pressure could be varied was built up to calculate the charged-particle density and electric field under different applied voltages.The continuity equations were solved by flux corrected transport algorithm and the Poisson equation was computed by the successive over relaxation method.The variations of important parameters due to air pressure were analysed.The particles densities of electrons,positive ions and negative ions at standard and low atmosphere pressures were computed,which increased markedly due to the decrease of atmosphere pressure.At fixed applied voltages,the exponential decay law between the maximal values of electron/positive ion densities at the head of the streamer and air pressure could be obtained.The quantitative law between the maximal values of electron/positive ion densities at the head of the streamer and the applied voltage,relative air density was also achieved.

Heat dissipation characteristics of anode saturable reactors with high thermal conductivity epoxy resin used for ultra-high-voltage direct current converter valves

A saturable reactor is one of the important components of converter valves in high-voltage direct current transmission systems.With the ever-increasing capacities of converter valves,the heat losses generated by saturable reactors are also increasing.Thus,a thermal-fluid mechanics coupled heat dissipation model for saturable reactors is proposed.In order to study the factors affecting the thermal dissipation in the saturable reactor,the epoxy resin insulating layers with different thermal conductivity were considered in this work.The simulation results showed that the hot spots in the saturable reactor are on the iron core and close to the pipe inlet that most of the generated heat can be extracted by a cooling pipe and that the effect of heat dissipation can be improved by raising the thermal conductivity of the epoxy resin.The thermal conductivities of the epoxy resin used in the two reactors were 0.8 and 1.2 W/mK,respectively.The time dependence of the iron core temperature was in accordance with the simulation results and the maximum temperatures of the saturable reactor were also consistent with the simulation results.By increasing the thermal conductivity of the epoxy insulation layer,the temperature of the iron core could be significantly reduced.

Roles of UV light strength and auxiliary electric field in the photocatalytic degradation effect of organic contaminant

The accumulation of contaminants on the electrical devices could adversely affect the operation.The present work used photocatalytic functional material to coat on the surface of the electrical devices to prevent the influence of organic contamination.This kind of material was mainly composed of TiO_(2)that can remove the contamination by the effect of photooxidation.The photocatalysis was affected by the strength of UV light and electric field.In the experiment,methyl orange(MO)was used as the organic contaminant.The effect of UV light and auxiliary electric field were analysed based on the theoretical simulation.With the stronger UV light,more electron-hole pairs were generated,photocatalytic effect became more pronounced.With the auxiliary electric field,the recombination of electron and hole could be restrained that would increase the productive rate of hole;therefore,more hydroxyl radical will be produced to degrade MO.

Experimental studies on effects of surface morphologies on corona characteristics of conductors subjected to positive DC voltages

As the surface conditions play a significant role on corona discharge and its related effects of the conductors,the influence of fine particulate matter on positive-polarity,direct-current conductors was studied experimentally in this study.The surface morphologies of the conductor could be discovered from the experiments.The typical morphologies are the parallel chains of particles.To evaluate the surface condition quantitively,the surface roughness of the conductors is measured.It is found that the applied voltage and testing time have a great influence on the surface condition.After that,the corona characteristics of conductors are tested.It reveals that the total ground level electric field and ion flow density increases with the surface roughness growing.