液体介质快脉冲电压下击穿特性研究

设计了液体介质快脉冲击穿试验装置和电压电流测量系统，研究了重复频率、电极形状及电极间距与介质击穿场强、击穿电压和击穿时延等击穿特性参数的关系，比较了变压器油、十二烷基苯、蓖麻油三种典型液体绝缘介质在直流及快脉冲电压作用下的绝缘性能。结果表明:短脉冲持续时间下液体绝缘材料有异常高的击穿场强；重复脉冲串作用下的击穿场强比单个脉冲下明显减小，重复频率2 kHz时击穿场强减小了约30％；电极头半径大小对击穿也有影响，半径R＝5 mm时，击穿电压最高；击穿时延随击穿场强减小而变长，在其他条件相同的情况下，测得击穿时延随机波动；蓖麻油的快脉冲电压绝缘性能最好，变压器油次之。     

重频纳秒高压脉冲下变压器油击穿特性的实验研究

介绍了重频纳秒高压脉冲下变压器油绝缘特性研究的现状和成果。进行了重频（1 Hz～1 kHz）纳秒高压脉冲下25#变压器油击穿特性的实验研究。实验发现相对于单次纳秒脉冲，重频脉冲下25#变压器油的击穿场强与频率相关，频率提高，击穿场强降低，但不是线性关系，在频率超过100 Hz时变压器油的击穿场强变化较小，在10~100 Hz时变压器油的击穿场强迅速下降。初步总结了重复频率、脉冲宽度和击穿场强的关系，对重频脉冲下变压器油的击穿机理进行了初步的探讨。     

高压重复频率快脉冲下变压器油中的闪络

介绍了重复频率快脉冲下固/液体介质交接面闪络初步的实验结果.脉冲功率源为基于半导体断路开关(SOS)的SPG200,固体介质为有机玻璃和尼龙,液体介质为变压器油.在相对低频阶段,闪络耐压时间与闪络场强随外加电压脉冲频率的增加非线性迅速减小,在约200 Hz以后,两者下降的趋势明显减缓.随着脉冲频率的增加,闪络耐压时间在统计上变小的同时,在一定区间内的分布也更均匀.分析表明,在不同实验条件下,重复频率显著低于单次下的沿面闪络和体击穿场强.两类场强都随脉冲频率增加非线性下降,在约200 Hz以后,下降的程度减弱.闪络场强随重复频率电压脉冲频率的变化表明,电压作用时间是绝缘介质击穿的根本要素,脉冲电压对绝缘介质的作用时间越长,沿面闪络越容易发生.     

极不均匀电场下重复频率纳秒脉冲气体击穿实验研究

 实验研究了尖-板电极中，不同重复频率（10,100,500,1 000 Hz）、不同间隙(0.5,1 cm),不同气压（0.1～0.4 MPa）等条件下空气的绝缘特性。得到了击穿时延、重复频率耐受时间、施加脉冲个数等与施加电压、重复频率的关系。研究发现：在该实验条件下击穿时延随着场强与气压的比值减小而增加，但重频耐受时间和脉冲击穿个数并没有明显变化；随着重复频率的提高，击穿时延和重频耐受时间会减小，但脉冲击穿个数可能会增加；且重复频率条件下击穿的极性效应不明显；重复施加的脉冲产生大量的亚稳态粒子和残余电荷影响放电的发展过程；负离子的脱负或正离子碰撞阴极的过程，及亚稳态粒子的去激励作用给击穿提供了有效初始电子。     

直流叠加脉冲电压下FLTD气体开关击穿特性

分析了直流叠加脉冲电压(定义为复合电压)下次级感应电压触发快脉冲直线变压器驱动源(FLTD)中气体开关击穿延时过程,给出了击穿延时的估算公式。初步实验研究了FLTD用三电极气体开关在复合电压作用下的击穿特性,结果表明:在±70kV直流充电电压叠加300kV/30ns快脉冲电压的复合电压作用下,气体开关的击穿延时小于相同工作系数下常规触发方式的击穿延时,采用SF6气体绝缘时,击穿延时较常规触发方式减小了17%~30%;采用N2绝缘时,减小了约50%,开关工作系数为55%时,击穿延时抖动小于5ns;理论估算的复合电压下击穿延时与实测结果基本吻合。     

基于Tesla变压器和Blumlein线的低抖动重频脉冲发生器

为实现MV级多级气体开关精确触发控制, 提出了基于Tesla变压器和Blumlein线的低抖动重频脉冲发生器的电触发方案。完成了Tesla变压器与Blumlein线一体化设计;优化了初级回路结构及绝缘栅双极型晶体管触发控制电路, 减小了初级杂散电感, 缩短了变压器次级高电压建立时间及时延抖动;优化了百kV级自击穿气体开关工作参数, 研制出一套多级低抖动电晕稳定开关;将传统Blumlein线绝缘介质由变压器油更换成高介电常数的MIDEL7131新油, 增加了输出脉冲宽度, 进一步提高触发能力。最终研制出一台输出电压130 kV、脉冲宽度大于5 ns、重复频率50 Hz、连续工作时间1 min、输出抖动小于10 ns的紧凑型脉冲发生器。     

压力水介质脉冲击穿实验研究

 为了提高水介质脉冲形成线的储能密度和减小大型加速器的脉冲功率系统几何尺寸，实验研究了水在静压力作用下的耐压强度。简要介绍了液体绝缘介质的击穿机理，在设计的水介质耐压实验装置上研究了去离子水介质在压力作用下的脉冲击穿特性。结果表明，当压强由0.1MPa增加到0.7MPa时，水的击穿场强由25.3MV/m增加到46.7MV/m。     

纳秒脉冲下几种液态介质绝缘性能的比对

利用自行研制的纳秒脉冲实验平台(输出脉冲前沿30 ns,半宽百纳秒)和标准介电强度测试仪,对变压器油、甘油、去离子水、Galden HT200四种液体绝缘介质在直流与纳秒脉冲下的击穿特性进行了实验研究与结果比对,结果表明:在直流与纳秒脉冲下,Galden HT200均具有最高的击穿场强,且两种情况下均比变压器油高出40%以上;纳秒脉冲下,Galden HT200与变压器油的击穿场强均提高6.5~7倍,Galden HT200击穿过程耗时最短(ns量级),其次是变压器油(20 ns),然后依次为甘油(45 ns)和去离子水(70 ns);多次放电后,粘度系数最大的甘油更易在电极间隙处聚集碳化放电产物,粘度系数较小的Galden HT200和去离子水则无明显痕迹,但二者放电过程会产生明显的冲击波,多次放电后易造成间隙电极松动。     

脉冲变压器锥形绕组电压分布数值分析

为实现高压、大电流脉冲变压器在高重复频率电压作用下稳定运行，变压器的绝缘选择与布置是其设计时重点考虑的问题之一。在短脉宽、高幅值的电压作用下，变压器绕组本身形成了一个不均匀场，如果绕组绝缘结构设计不当，就很容易在绕组的局部产生畸变的强电场，导致变压器绕组击穿，对脉冲功率发生装置的研制工作造成了极大的危害。这种现象在高频下更为明显。因此，研究高功率脉冲变压器绕组的电压分布，采用适当的措施实施有效方法进行绕组结构优化设计，改善高功率脉冲变压器绕组的电压分布，将会在很大程度上提高高功率脉冲变压器重复工作的能力，对保证高功率脉冲发生器可靠、安全运行具有重要的理论与工程意义。     

重复频率纳秒脉冲聚四氟乙烯薄膜击穿特性

实验研究了聚四氟乙烯薄膜在重复频率纳秒脉冲下的击穿特性,选用脉冲上升时间约15 ns,脉宽30~40 ns,重复频率1~1 000 Hz。测量并计算了击穿前后的电压电流波形、重复频率耐受时间和施加脉冲个数与击穿特性密切相关的参数。结果表明,重复频率纳秒脉冲下聚四氟乙烯薄膜击穿场强为MV/cm量级,重复频率耐受时间随施加场强和重复频率的增大而减小。薄膜本身性质及油浸时间使实验数据具有分散性,重复频率纳秒脉冲下聚四氟乙烯薄膜击穿应考虑重复频率条件下的热积累效应和材料缺陷。     

Study on dielectric surface discharge in transformer oil under high voltage nanosecond pulse

Electrical equipments are always subjected to different operating conditions and voltage waves which cause electrical failure on the surface and in the bulk of dielectrics. In this paper, experiments have been carried out to study main factors that influence the characteristic of dielectric surface discharge in transformer oil. Experimental study on flashover of nylon 6 and polymethyl methacrylate (PMMA) under applied voltage ranged from 50 to 250 kV shows that the flashover voltage U is influenced by the insulation structure, rise velocity and pulse width of the applied voltage. Flashover electrical field value E in pulse with rise time less than 10 ns is higher than that in DC and AC voltages. When angle between electrode and the sample is about 45°, nylon 6 and PMMA show the best flashover performance. From these results, the influence of the secondary electron emission and space charges on the electrical breakdown of dielectrics has been stressed.     

Contribution to static electrification of mineral oils and natural esters

A failure of an insulation system of a power transformer can result into an interruption of a power supply and subsequently to a large economic damage. In some cases, the malfunction is so serious that a transformer may explode and catch fire resulting in a direct threat to the life of the device operator. These devices rely on a combined insulation system oil-paper. The oil in a transformer not only impregnates the pressboard paper insulation, hence increases its electric breakdown strength, but also acts as a coolant of active parts of the device. During the cooling, the oil flows in the transformer tank around the core, windings and isolation barriers from hardened paper. At the interface of two dielectrics, the oil and the cellulose in the transformer, electrostatic charges appear. The charges of one polarity are carried in the oil, and the charges of the opposite polarity remain captured in the barrier that is formed by the internal structure of the transformer. The accruing of a certain amount of charge leads to discharges along the surface of the solid insulation and therefore to its partial damage. Ultimately, this can lead to the damage of the whole insulation system of the transformer by its breakdown. At present, the mineral oils are used as the main liquid insulating medium because of their good electrical insulating and cooling properties. On the other side, there is a high environmental burden for their operation and maintenance as well as the subsequent disposal of the discarded oil. The natural esters may be used as a replacement for the mineral oil. They go well with the environment, they are biodegradable and in case of the transformer malfunction, its disposal costs less money.This paper presents the results of the experiments of electrostatic charging of the mineral oils and natural esters and their comparison. The charging process in the transformer is modelled using a metal cylindrical container with a forced flow of oil using a controlled rotating circular disc from a hardened paper. The results indicate that increasing intensity of friction, increases the electrical charge, which is generated at the interface of the solid phase and the liquid. In these experiments two types of mineral oils were studied. For comparison, two types of natural esters (sunflower and colza oils) were selected and used in the same experiments. The charging of the oils was examined at various temperatures ranging from 25 °C up to 70 °C.     

Electrical breakdown of transformer oil with sulfur hexafluoride and air bubbles

Technical Physics - The influence of gas bubbles on the breakdown voltage of transformer oil is experimentally studied. The influence of the oil flow on the electrical characteristics of breakdown...     

正极性纳秒脉冲电压下变压器油中流注放电仿真研究

建立了二维轴对称流体模型, 仿真研究了正极性纳秒脉冲电压下变压器油中针-板电极流注放电的起始与发展过程, 得到了不同的外施电压幅值、脉冲上升沿时间与电极间隙距离下油中流注放电的形貌、 电场强度与空间电荷密度分布等. 仿真结果表明: 空间电荷加强了流注头部前方电场, 使流注通道更易于向前推进, 形成"电离波"; 随着外施电压幅值升高, 流注发展的平均速度显著变大; 较陡的脉冲上升沿形成的放电半径较大, 对应的最大电场强度值变小; 随着电极间隙距离的增加, 流注发展平均速度变快. 仿真显示纳秒脉冲下放电中油温无明显升高, 表明此类放电过程没有明显的油气化现象. 我们认为, 场致电离是油中带电粒子产生的主导机制; 空间电荷效应增强流注前方电场使得电离进一步发展, 最终导致击穿. 本研究有助于加深对变压器油中放电起始、发展直至击穿过程的认识以及对液体电介质中电离机制的理解. 关键词： 变压器油 流体模型 流注放电 空间电荷效应     

Influence of solitary gas bubbles on the electrical breakdown of transformer oil

The influence of solitary gas bubbles on the breakdown voltage of transformer oil is studied experimentally. It is shown that discharges periodically arise in bubbles at fields lower than the oil breakdown field.

     

一种油介质开关振荡器研究

为了产生较高中心频率宽带高功率微波, 对一种填充变压器油作为绝缘介质的1/4波长开关振荡器进行了研究。首先对这种开关振荡器特性阻抗分布进行了分析;然后利用静态电场仿真结果和变压器油击穿实验数据, 分析了该振荡器的耐压能力;在此基础上, 利用CST软件对其瞬态工作特性进行了仿真, 考察了开关间隙击穿位置和间隙电压下降时间对产生阻尼正弦信号的峰值和频率的影响;最后介绍了该振荡器以一种方向系数为3的短螺旋天线作为辐射天线的实验测试结果, 结果表明, 该开关振荡器充电电压上升时间为15 ns时, 耐压达到-322 kV, 产生宽带高功率微波中心频率约360 MHz, 3 dB带宽约22%, 辐射因子170 kV。     

Electrical breakdown theory for a two-component system

The field distribution between the liquid and solid phases is calculated for pulse tests of breakdown of sodium chloride, coal, and cuprous sandstone in water and in transformer oil, taking account of the phenomenon of polarization build-up. Conditions for breakdown without flashover are found. The rupture mechanism is investigated for a two-component system in pulsed electric fields.     

微秒脉冲下碳酸丙烯酯的击穿特性

采用紧凑Tesla变压器型脉冲功率驱动源及球电极击穿试件,通过改变初级充电电压,开展了微秒级充电条件下碳酸丙烯酯及其与碳酸乙烯酯的混合液的击穿实验研究。由结果和分析可知:碳酸丙烯酯理论工作温度可低至-55℃,这意味着它可以成为一种低温下的良好液体电介质;碳酸丙烯酯耐压性能与去离子水相当,且实测电阻率达到了10 MΩ·cm以上;向碳酸丙烯酯中添加碳酸乙烯酯后,介电常数可提高至80以上,耐压强度也有所提升;将碳酸丙烯酯、碳酸乙烯酯/碳酸丙烯酯混合液用于脉冲形成线作为储能介质无需附加去离子处理系统,有利于装置的紧凑化和小型化。