同轴电极固液界面放电的碎石模式

为了提高高压脉冲碎石效率,开展了同轴电极固液界面碎石实验研究。采用高电压脉冲放电原理,设计了同轴电极平面布置在固体介质表面,利用液体绝缘的高电压脉冲放电碎石实验装置,开展了不同液相绝缘介质中不同固相介质条件下的高电压脉冲碎石实验。经过对记录的电压电流波形进行比较分析,抽取了可能的区分不同放电模式的参数特征。结果表明:液体介质击穿时延比相应环境下固体介质击穿时延大,且击穿时延与液体介质的导电粒子含量负相关;液体介质击穿电阻变化系数比其环境下固体介质击穿电阻变化系数大至少一个数量级。根据分析得出击穿时延与击穿过程电阻变化系数可以作为判别放电模式的参数特征。     

百纳秒脉冲下水压对水开关击穿特性的影响

以俄罗斯西伯利亚研究院通过实验总结出的液体介质气泡击穿理论的全新阐述作为理论基础,开展了300 NS短脉冲下高压强水介质开关的击穿实验,获得了该条件下水介质击穿场强及耐压时间与水中压强关系的数据。结果表明在300 NS脉冲电压实验平台下,当水介质场强变化率为2~3 MV/CM时,水介质击穿电压和耐压时间均随着水中压强的提高而呈上升趋势,且趋势越来越显著。     

双极性加载脉冲源中储开关同步击穿特性

采用2级压缩回路和双极性脉冲叠加技术可以获得高电压快脉冲,但这对脉冲源各级开关同步特性要求较高。为研究初级源对中间储能电容器充电时间约120 ns时中储开关击穿特性对脉冲源运行的影响,文中分析了一种双极性加载脉冲源对中储开关同步击穿的要求,通过实验获得了自触发预电离中储开关在相应充电时间下的击穿电压、时延及抖动特性,并根据实验数据计算了正、负极性脉冲下中储开关击穿时延差值的概率分布。结果表明,该双极性脉冲源需要控制中储开关击穿时延差值小于10 ns;自触发预电离中储开关在0.2～0.7 MPa氮气中、不同极性脉冲下的击穿时延抖动均小于3 ns;取99.99%置信区间时,气压0.5～0.7 MPa时正、负极性中储开关击穿时延差值小于10.8 ns。该结果可作为考核中储开关同步特性和分析峰化电容器绝缘裕度设计要求的参考。     

350kV可变脉宽的纳秒脉冲发生器

介绍了可产生 35 0 k V脉冲方波且脉宽可变的脉冲发生器。装置由 Marx发生器产生纳秒级脉冲电压 ,对成型线充电后由主开关对负载电阻放电 ,在负载电阻上得到 ns级脉冲电压。改变 Marx输出电压、主开关击穿电压和负载电阻阻值 ,可调节输出 ns脉冲的幅值 ;改变成型线的长度可改变输出脉宽     

液体介质击穿机理研究进展

在参阅大量文献的基础上,给出当前液体介质击穿理论的最新进展及成果:电子理论、气泡理论、小桥理论,并且比较分析不同理论的优缺点,指出纳秒脉冲液体击穿机理研究的独特性,供该领域的研究者借鉴。     

纳秒级高压脉冲下绝缘击穿特性的研究

研究了液体和固体绝缘材料的击穿特性 ,通过蓖麻油、变压器油、聚酯薄膜、聚酰亚胺薄膜的击穿实验的波形处理和分析 ,说明了击穿电压与脉冲陡度、脉冲宽度和作用时间的相互关系 ,相对于直流、慢过程条件下绝缘击穿特性 ,纳秒级快脉冲下绝缘材料的击穿场强会大幅提高 ,其击穿场强随脉冲缩短而提高 ,但作用减小。给出了一些具体的绝缘材料击穿值     

纳秒脉冲电压下变压器油预击穿特性的仿真分析

以针—球电极间隙变压器油为研究对象,基于场致电离机理,建立用于表述液体电介质流注预放电过程中载流子的产生及输运的偏微分方程,结合电场泊松方程,以及热扩散方程,仿真研究纳秒脉冲电压下变压器油预击穿特性。得到了预击穿过程中电场强度随电压幅值、极性以及脉冲上升沿时间的变化规律。仿真结果表明:流注速度随电压幅值的增大而增大;负流注相比于正流注轴向传播距离小径向传播距离大;负流注起始放电电压高于正流注,且起始速度大于正流注;正脉冲上升沿时间越短所形成流注半径越大,上升沿时间大于50 ns的负脉冲条件下产生的流注易消散。本文的研究工作和取得的结论有助于加深对变压器油中放电起始、发展过程的认识以及对液体电介质放电机制的理解。     

纳秒脉冲气体放电机理研究现状

针对脉冲功率技术一基础研究领域即ns脉冲下电介质击穿机理 ,详析了几种放电机理假说 (包括经典流注机理、电子崩链模型、逃逸电子模型、气体开关模型等 ) ,指出重频ns脉冲下气体放电试验及机理值得研究。     

纳秒脉冲下SF6气体放电特性

随着电力系统电压等级的提高,特快速暂态过电压(very fast transient overvoltage,VFTO)对气体绝缘变电站(gas insulated switchgear,GIS)的安全稳定运行产生了越来越严重的威胁,为了提高设备运行的安全稳定性,促进设备小型化,需要深入分析VFTO下SF6气体的绝缘特性。因而该文利用基于半导体断路开关(SOS)的ns脉冲源SPG 200N的输出电压模拟VFTO波形的快速上升过程,黄铜板-板电极模拟GIS内的均匀场,研究了ns脉冲下SF6气体的放电特性,得到了重频耐受时间、施加脉冲个数等与重复频率的关系。实验结果表明,重频耐受时间随着脉冲重复频率的提高而降低,但击穿前所施加的ns脉冲个数与重复频率的关系比较复杂。随着气压的升高,临界击穿场强与气压的比值E/p有所下降,但在该文研究范围内其值仍高于理想状态下稳态电压对应的单位气压下临界值88.5kV/(mm.MPa)。获得的SF6放电特性为进一步明确VFTO下SF6气体的放电机理提供了实验依据。     

纳秒脉冲下有机玻璃电树枝老化特性研究

介绍了有机玻璃(PMMA)在纳秒脉冲作用下电树枝引发和生长的规律现象。采用压紧针电极与绝缘样品接触、多针并列式的方法制备实验试样,绝缘样品(有机玻璃)加工为120mm×5mm×2.5mm的长方条。实验使用产生30ns上升沿和70ns脉冲宽度的负脉冲固态纳秒脉冲发生器MPC50D作为激励源,在25℃的条件下,施加100Hz的重复频率脉冲,设定初始电压,逐级升压,直至引发电树枝后停止升压,记录电树枝引发电压,观察电树枝生长特点及现象。实验发现PMMA中电树枝出现裂隙状破坏,经过分析讨论,认为是力作用导致的结果。实验中还观察到电树枝生长速度极快的现象,从电树枝引发到击穿只需几秒钟。通过研究证明绝缘油浸入导致了电树枝生长加速,深入讨论分析了绝缘油浸入促进电树枝快速发展的原因、机理及抑制方法。     

注入空间电荷对SF_6气体中尖—板间隙正冲击击穿电压的影响

在充SF_6或N_2的尖—板间隙中注入适量正空间电荷能使正极性冲击击穿电压提高,而注入负空间电荷则使正冲击击穿电压降低。用这一实验结果可以解释以前发现的含氯添加气体使尖—板间隙中SF_6的正冲击击穿电压提高的实验现象。     

Streamer initiation in mineral oil. Part II: influence of ametallic protrusion on a flat electrode

For pt. I see ibid., vol. 9, no. 1, p. 84-91 (2002). Presents a study of streamer inception in transformer oil, in a "semiuniform" geometry under impulse voltage. This geometry consists of parallel plane electrodes, with a thin triggering point of calibrated size emerging at the center of one plane. By reducing the length of the point, it is possible to move progressively from a point-plane geometry, up to a quasi-uniform geometry. Compared to a point-plane gap, the initiation of streamers is impeded due to the presence of a metallic plane behind the triggering point, that reduces the tip field. Field calculations allow to extrapolate the results obtained to the case of microscopic surface protrusions and particles. It is possible to predict the streamer initiation voltage, and hence the breakdown voltage under uniform field, from the shape of the protrusion and from streamer initiation fields measured in point-plane geometry     

Surface flashover of oil-immersed dielectric materials in uniform and non-uniform fields

The applied electrical fields required to initiate surface flashover of different types of dielectric material immersed in insulating oil have been investigated, by applying impulses of increasing peak voltage until surface flashover occurred. The behavior of the materials in repeatedly over-volted gaps was also analyzed in terms of breakdown mode (some bulk sample breakdown behaviour was witnessed in this regime), time to breakdown, and breakdown voltage. Cylindrical samples of polypropylene, low-density polyethylene, ultra-high molecular weight polyethylene, and Rexolite, were held between two electrodes immersed in insulating oil, and subjected to average applied electrical fields up to 870 kV/cm. Tests were performed in both uniform- and nonuniform- fields, and with different sample topologies. In applied field measurements, polypropylene required the highest levels of average applied field to initiate flashover in all electrode configurations tested, settling at ~600 kV/cm in uniform fields, and ~325 kV/cm in non-uniform fields. In over-volted point-plane gaps, ultra-high molecular weight polyethylene exhibited the longest pre-breakdown delay times. The results will provide comparative data for system designers for the appropriate choice of dielectric materials to act as insulators for high-voltage, pulsed-power machines.     

Streamer propagation under impulse voltage in long point-plane oilgaps

A 67 mm point-plane gap immersed in transformer oil, at atmospheric pressure, stressed with a 1/180 μs impulse, has been studied by recording gap current and light emission. Time-resolved images were obtained by use of an image converter camera. Minimum breakdown voltages were twice as high for negative as for positive points. All streamers at these and higher voltages were supersonic, with negative streamer velocities ⩽50 km/s. The speed of the positive streamer gradually increased to 19 km/s with increasing voltage, where it saturated. At high stresses the propagating positive streamer has been observed to switch to a faster mode which propagates with speeds in the 65 to 200 km/s range. Positive streamers were bush shaped to 2× the minimum breakdown voltage, the branching diminishing with increased voltage. Negative streamers were coarsely bush shaped or usually tree shaped. For both polarities, light emission consisted of a background light, with superposed pulses corresponding to 15 ns wide current pulses of up to 10 A. The pulses are caused by very bright, brief re-illuminations of single streamer channels. The tips of positive streamers are considerably more luminous than the channels, indicating that electron multiplication may take place at the tips. A model of the streamers as being plasma filled channels may explain the re-illuminations     

高压脉冲方波下聚酰亚胺薄膜电老化寿命模型

逆变器输出的高压脉冲方波会导致变频调速牵引电机绝缘过早损坏,其老化机理与工频交流电压下不同.利用一种高压脉冲绝缘老化试验系统模拟变频器对变频调速牵引电机定子绕组绝缘的老化作用,以聚酰亚胺薄膜为试验对象,研究了脉冲方波幅值、频率对绝缘寿命的影响,提出了高压脉冲方波下绝缘材料的电老化寿命模型.     

Streamer initiation in mineral oil. Part I: electrode surfaceeffect under impulse voltage

Presents a study of streamer inception in mineral transformer oil, in point-plane and rod-plane geometry under impulse voltage. The measurements performed with points and rods over a wide range of tip radii show a marked decrease of initiation fields when the electrode radius is increased. The initiation field is divided by 30 over the investigated range (from 1 μm points up to 2 cm rods). This effect compares fairly well with the "surface effect" known for breakdown voltages under uniform field with large electrodes. Plotting these results together shows the decrease of streamer initiation fields over a very wide electrode surface range (12 decades), proportional to S^-0.17 (S: electrode surface area, cm²). These results suggest the influence of electrode surface defects on streamer initiation under impulse voltage     

常压下重频纳秒脉冲气体放电试验研究

气体介质在重频(PRF)纳秒脉冲作用下的绝缘特性是高重频脉冲功率技术研发的基础。采用SPG200重频纳秒脉冲电源，通过测量常压空气介质间隙(5、10、15、20mm)，在不同重复频率(1、10、100、500、1000Hz)、不同电压幅值(60、80、100kV)作用下的击穿电压、电流、击穿延时及耐受时间，研究了空气的绝缘特性。结果显示重频脉冲常压下空气的击穿场强比单次脉冲时低得多；随击穿场强的增大，击穿时延、重频耐受时间均有减小的趋势，高PRF时减小趋缓。低PRF下的放电发展过程与单次时的放电发展过程差别不大，而与高PRF下的不同。最后对纳秒脉冲下击穿时延及放电机理等进行了一些讨论。     

Dielectric characteristics of turn-to-turn insulation models of gas-insulated transformer under very fast transient voltages

This paper deals with the partial discharge inception voltage (PDIV) and breakdown voltage (BDV) characteristics of turn-to-turn insulation models for SF₆ gas-insulated transformers in the presence of steep-front short-pulse voltages, whose waveforms are 35/65 ns and 50/370 ns. It was determined that PDIV at nanosecond pulses were 1.05 to 1.15 times higher than those at standard impulse voltages and that the BDV at nanosecond pulses were about 1.4 times higher than those at standard impulse voltages. The ratio of impulse PDIV to ac PDIV is 1.40 to 1.48 for standard impulse voltages and 1.32 to 1.37 for switching impulses. © 1998 Scripta Technica, Inc. Electr Eng Jpn, 121(3): 36–43, 1997     

Initial images of complete breakdown of liquid nitrogen/polymerfilm

This paper describes an experimental study,on the prebreakdown phenomena in a liquid-nitrogen/polymer-film composite subjected to dc ramp and step voltages under point-plane electrode system. In order to clarify the formative process of the complete breakdown of the composite, photographic observation was carried out using a long image guide scope and an image intensifier with high speed gate in the nanosecond region. When a negative-plane electrode was covered by a polymer film (N-cover arrangement), a luminous region on the initial image of the complete breakdown was located near the negative-plane under both the ramp and the step voltages. These results suggested that the complete breakdown of the composite in the N-cover arrangement was caused by the film breakdown due to positive charges deposition and subsequent electron emission from the film breakdown spot. When a positive-plane electrode was covered by the film (P-cover arrangement), film breakdown could not trigger the complete breakdown under the ramp voltage because the film breakdown occurred at a low applied voltage. However, intense light near the positive-plane was observed at the initial stage of the complete breakdown under the relatively high step voltage. This was because the film breakdown under the high applied voltage induced the positive streamer propagation from the film breakdown spot     

Breakdown conditioning characteristics of long gap electrodes in a vacuum

An improvement in dielectric strength is required in vacuum circuit breakers (VCBs) intended for use in higher voltage systems. In order to develop higher voltage VCBs, it is important to improve the dielectric strength in a vacuum based on consideration of the vacuum breakdown mechanism. Particularly for gaps longer than 10 mm, little is known about the breakdown mechanisms and their quantitative analyses in a vacuum. This paper discusses the breakdown conditioning characteristics of long gap electrodes, under a non-uniform electric field in a vacuum. We treat gap lengths of up to 50 mm in this paper. The conditioning characteristics are investigated under impulse voltage applications. A negative standard lightning impulse voltage was applied to rod-plane electrodes made of Cu-Cr and SUS304 for different tip radii and gap distances until the conditioning effect was completed. We observed illumination spots on electrodes at each breakdown during the conditioning process and calculated the corresponding breakdown field strengths. Experimental results revealed that the tendency of breakdowns associated with long gaps is different from that for the short gaps. As a result, we clarified that the breakdown field strengths are nearly constant at 110-120 kV/mm at the distances longer than 10 mm, and the breakdown field strength is at its maximum when the gap distance is about 5 mm.