SF_6—CO_2混合气体的绝缘强度

研究表明,虽然SF_6—CO_2混合气体在均匀电场中的击穿强度稍逊于同样混合比的SF_6—N_2混合气体,但在不均匀电场中的击穿强度、特别是在雷电冲击电压下的击穿强度,却优于SF_6—N_2.此外,SF_6—CO_2在气膜复合绝缘中的局部放电特性也优于SF_6—N_2混合气体.     

-50℃条件下SF_6/N_2混合气体的击穿特性

为研究低温条件下SF_6/N_2混合气体的击穿特性,搭建了温度可控的气体击穿试验系统,采用棒板电极模型模拟GIS内部极不均匀电场,对SF_6/N_2混合气体的工频及雷电冲击击穿特性进行了研究。结果表明:只要保证固定的充气比例和密度下混合气体不发生液化,温度变化对SF_6/N_2混合气体的绝缘性能基本无影响,且SF_6/N_2混合气体的极性效应比纯SF6气体更明显。     

管道母线(GIL)中SF_6/N_2混合气体绝缘性能的研究

文中首先对GIL中SF_6/N_2混合气体的绝缘性能进行了计算,重点关注了SF_6体积分数配比以及气体压力对绝缘能力的影响,并且研究了高落差下是否出现气体分层从而对混合气体的绝缘能力产生影响。其次,利用试验装置,对SF_6/N_2混合气体在不同配比和压力下的雷电击穿电压进行了测量,并且对比分析了试验结果与计算结果的差异。计算结果表明SF_6/N_2混合气体绝缘强度随SF_6气体体积分数增加而提高,但SF_6体积分数达到10%后,混合气体的击穿电压呈现出饱和的趋势;在高落差下,SF_6和N_2的混合比随高度的变化很微小;GIL样机的雷电冲击试验结果验证了击穿电压计算结果的正确性。     

冲击电压波形对GIS由固定导电粒引发的击穿电压的影响

作者研究比较了正极性冲击电压波形对SF_6、空气、SF_6/空气的GIS电极装置由固定导电微粒引发的击穿电压的影响,结果表明:SF_6间隙的击穿电压受冲击电压波前时间长短的影响较大,而与波长的关系不大,当采用SF_6/空气混合气体时,则这种影响随SF_6含量增大而愈明显,并与电场不均匀程度有关。     

用预放电电流法测量SF_6和SF_6/CO_2气体的离子迁移率

用预放电电流法测量了SF_6气体以及SF_6/CO_2混合气体的正负离子迁移率。实验数据表明,正负离子迁移率只是E/p的函数,SF_6/CO_2混合气体的正负离子迁移率随CO_2含量的增加而增大。     

两种典型电极下SF_6/CF_4混合气体击穿特性的实验研究

针对板—板、针—板两种典型电极形状在5 mm间隙下SF_6/CF_4混合气体的击穿特性开展实验研究,分别测量SF_6分压比为0%~100%、压强在0.1~0.6 MPa下的气体击穿电压,研究压强、SF_6分压比及电场不均匀度等因素对SF_6/CF_4混合气体绝缘性能的影响。结果表明:0.6 MPa的20%SF_680%CF_4气体在板—板电极下的击穿电压为138.89 k V,是相同压强纯SF_6气体击穿电压的64.8%,在针—板(针为负极性)电极下的击穿电压为58.4 k V,是相同压强纯SF_6气体击穿电压的74.8%。在压强一定时,SF_6/CF_4混合气体的击穿电压与SF_6的分压比呈非线性增加,但随电场不均匀程度的增大,SF_6分压比的变化对击穿电压的影响逐渐减弱,随SF_6分压比的增大,混合气体的协同效应明显降低;在SF_6分压比一定时,随压强的增大,混合气体的协同效应增强。     

SF6/N2混合气体的工频击穿特性研究

通过理论分析对SF_6/N_2混合气体的工频击穿特性进行了研究,得出SF_6/N_2混合气体中SF_6气体的最优比例是20%～30%,同时在其他条件不变的情况下将混合气体压力提高至1.4倍即可具备与纯SF_6气体相同的工频击穿电压。试验结果也验证了分析结论的正确性,表明SF_6/N_2混合气体代替纯SF_6气体作为绝缘介质是完全可行的。     

密闭空间中温度对SF_6/N_2混合气体工频击穿电压的影响规律

气体绝缘组合电器会遇到不同的环境温度,为优化SF_6/N_2混合气体设备的设计,研究SF_6/N_2混合气体在工频电压下的击穿电压随温度的变化规律,并分析温度对气体绝缘性能的影响机理。首先分析SF6气体中的电子崩发展过程,发现温度降低导致SF6的附着反应减弱,从而降低其绝缘性能。为验证理论分析,通过试验得到-50℃、-35℃、-18℃、20℃四个温度下,稍不均匀和极不均匀电场中SF_6/N_2混合气体的工频击穿电压。发现在稍不均匀电场中,从20℃降低到-50℃时,SF_6/N_2混合气体的击穿电压降低约10%,在极不均匀电场中降低约12%。与SF_6的试验结果对比发现,稍不均匀电场中SF6的击穿电压随温度下降更显著,但极不均匀电场中SF_6/N_2混合气体的击穿电压随温度下降更明显。考虑导体温升,进一步对比了100℃高温下的情况,发现在-50℃至100℃温度范围内,SF_6/N_2混合气体的工频击穿电压随温度升高呈非线性增大趋势,试验现象验证了理论分析。为补偿极寒条件下SF_6/N_2混合气体的绝缘性能,应适当提高混合气体充气密度或提高SF_6比例。     

环保型C_4F_7N/CO_2混合气体在极不均匀电场下的雷电冲击绝缘特性

C_4F_7N/CO_2混合气体作为最新一代的环保型绝缘气体,具有优良的电气性能和低温室效应潜能值,有极大的替代SF_6的应用前景。目前,国内外的相关研究才刚刚起步。使用针–板电极模拟极不均匀电场,实验研究C_4F_7N/CO_2混合气体的雷电冲击击穿特性,分析气压、间距、混合比例等因素对混合气体绝缘特性的影响及其极性效应,并与相同条件下纯SF_6进行对比。结果表明:极不均匀电场中,C4F7N混合比5%～10%的C_4F_7N/CO_2混合气体正极性雷电击穿电压随气压的升高呈现明显饱和趋势,存在显著的"驼峰"现象,而负极性时击穿电压在较高气压时才逐渐趋于饱和;混合比为5%的C_4F_7N/CO_2混合气体正极性雷电击穿电压最高能够达到相同条件下SF_6的0.8倍,混合比为10%时最高可达相同条件下SF_6的0.9倍,负极性时C_4F_7N/CO_2混合气体相对SF_6绝缘强度略低于正极性;极不均匀电场中,C_4F_7N/CO_2混合气体雷电击穿电压存在明显的极性效应和极性反转现象,总体上负极性击穿电压显著高于正极性,仅在较低气压时正极性稍高。研究结果表明,C_4F_7N/CO_2混合气体非常有潜力替代SF_6。     

温度变化对SF_6/N_2混合气体放电特性的影响

不同温度下SF_6/N_2混合气体的周围离子平均自由行程和热运动速度不同,使SF_6/N_2混合气体放电过程呈现不同特性。为此,在极不均匀电场、雷电冲击电压下研究了温度对SF_6/N_2混合气体放电特性的影响。在正负极性的雷电冲击电压下分别测量冲击击穿电压和预放电电流波形,并分析了不同温度下SF_6/N_2混合气体的预放电现象、步长时间、电晕起始场强及击穿场强。此时试验温度范围设为-20~20℃。结果表明:步长时间、电晕起始场强、击穿场强呈现较大的随机性。负极性雷电冲击电压下步长时间均长于正极性雷电冲击电压下步长时间。负极性冲击电压下10%SF_6-90%N_2混合气体的电晕起始场强和击穿场强随着温度升高而增高。本研究结果对柜式气体绝缘开关设备和气体绝缘金属封闭输电线路设计具有一定的研究意义。     

The effect of the electrode gap on breakdown in liquid dielectrics

It is a well known fact that the breakdown voltage of an insulating liquid increases nonlinearly with increasing electrode gap. Under nonuniform field dc conditions two breakdown voltages are determined depending on the electrode polarity. Using point-plane geometries, with gaps of 5 mm or larger, one finds that typical transformer oils have higher breakdown voltages when the point is negative than when it is positive. Recently, perfluorinated polyethers have been found to produce opposite results when using average gap sizes of 5 to 10 mm. To elucidate this situation a study of the effect of gap size on breakdown voltage has been undertaken. The results show that for the polyethers at larger gaps the sequence is reversed. These observations are explained in terms of the respective streamer developments in these liquids and the relative stability of their negative ions. In the case of the conventional hydrocarbon type oils, the positive streamer usually grows slightly faster than the negative one, but the streamer inception voltages of both are rather similar. In the case of perfluorinated polyethers the positive streamers move at least 10× faster than the negative ones, but they require much higher inception voltages than negative ones. At gaps ≳12 mm and the associated higher applied voltages this breakdown at negative polarity occurs at higher voltages than at the positive one. The negative ions of the perfluoro compounds are much more stable than those of conventional hydrocarbons. The discharge of the negatively charged perfluoro ions requires much higher fields than do those of conventional hydrocarbons. The implications of these observations are discussed in some detail     

Prediction of breakdown in SF6 under impulse conditions

Prediction of fast transient voltage-induced breakdown in quasi-homogeneous field geometries requires compounding the breakdown probability over time, while taking into account the field-dependent probability of electron detachment. In this paper, a breakdown probability model has been developed to predict the impulse breakdown under quasi-uniform fields, as this is the fundamental condition, the knowledge of which facilitates computation of breakdown probability under more complex conditions. The model will facilitate computation of breakdown probability under more complex conditions. It accounts for the effect of the streamer formation length on the critical volume and the probability of initial electron production by electron detachment from negative ions. The proposed model has been verified through comparison with the measured impulse breakdown probabilities. The predicted breakdown probabilities are in good agreement (±10%) with those measured     

预电离对尖—板间隙冲击击穿的影响

实验发现,负离子的脱附作用是封闭尖-板间隙冲击放电的主要初始电子源.在空气中添加少量电负性气体SF_6或R12(CCI,F,),冲击击穿电压得到大幅度提高,这是由于形成了高稳定性的负离子的缘故.     

电晕离子流对先导放电路径的影响

为探明当空气中含有电晕产生的离子时(离子背景),对雷电先导的发展、击穿过程和路径的选择有何影响,分别采用两种不同的实验方法研究了正、负离子流对先导放电进展路径影响的特点及规律,两种方法得出的一致结果表明,有离子背景的雷电先导放电路径具有选择负离子背景而回避正离子背景的特点和规律并运用电子崩发展和电场作用两方面原理,分析了离子背景的影响机制。这对于特高压输电线路与设备的防雷及其绝缘设计的进一步研究具有重要参考意义。     

Breakdown Phenomena in Nitrogen Due to Repetitive Nanosecond-pulses

Nanosecond-pulse breakdown indicates special characteristics depending on the pulse rise-time and duration. Based on a repetitive nanosecond-pulse generator, breakdown phenomena of parallel-plane gaps in nitrogen were investigated with single pulse and repetitive bursts under different gap conditions. The relationships between applied voltage, pulse repetition frequency, breakdown time lag, repetitive pulse stress time and the number of applied pulses are presented. The curves regarding E-field strength, breakdown time lag and gas pressure are also obtained. The experimental results show that breakdown characteristics with repetitive nanosecond-pulses are different from that with single pulse. Repetitive nanosecond-pulse breakdown is concerned with the accumulation effect that is attributed to residual ions and metastable species survived from previous pulses. In addition, a modified empirical formula about E-field strength, breakdown time lag and gas density is given for the breakdown data.     

外施横磁下真空断路器弧后金属蒸汽击穿过程仿真研究

从微观的角度分析外施横向磁场下直流真空断路器弧后金属蒸汽击穿过程。首先,建立了可以描述直流真空断路器弧后金属蒸汽击穿过程的粒子模拟-蒙特卡洛碰撞仿真模型，确定了弧后金属蒸汽击穿判据；其次对比了不同横向磁场强度下弧后金属蒸汽击穿的发展过程，分析外施横磁强度对弧后金属蒸汽击穿的作用；最后，分析了外施横向磁场强度对弧后金属蒸汽击穿时刻的影响。研究结果表明：场致发射提供了金属蒸汽击穿的初始电子，是诱发金属蒸汽击穿的“种子”，电子崩的出现意味着金属蒸汽击穿的发生；横向磁场会降低真空间隙内的电子数和铜离子数，这是因为间隙内的电子和铜离子会在横磁的作用下横向扩散；横向磁场越大，金属蒸汽击穿速度越慢，当外施磁场由0 mT增加至2 000 mT时，击穿时刻由1.913×10^-7 s增加至2.72×10^-7 s。本文的研究结果有助于理解外施横磁下直流真空开断的弧后金属蒸汽击穿过程，可为低压直流真空断路器的开发提供理论依据。     

Influence of ground and corona currents on dielectric behavior of small air gaps

This paper investigates the influence of grounding on the field distribution and on the dielectric behavior of small rod-plate and rod-rod air gaps. This effect can be attributed to the grounding of one electrode. In the different arrangements with one electrode grounded or with the electrodes symmetrically charged the experimental results of the corona and breakdown are recorded and compared to the simulation results of the field distribution. It is resulted that the grounding influences significantly the electric field distribution, the dc corona and the dc breakdown. The field is less inhomogeneous in grounded rod - plate air gaps and in rod-rod air gaps with symmetrically charged electrodes, and consequently the values of the corona onset and the breakdown voltage are higher. In longer air gaps the corona current influences the field distribution and consequently the dc breakdown. The effect of grounding on the breakdown is weakened when the dc polarity of the voltage is negative, otherwise it is enhanced. In air gaps with lengths > 3 cm (negative dc polarity) or >8 cm (positive dc polarity) it is overlapped by the effect of the corona current. Relations between the field strength, the corona current, the corona onset and the breakdown voltage arise. The principle of action-reaction is valid.     

Impulse breakdown of insulators and air gaps of similar electrodeconfigurations: effects of temperature

Comparative measurements are reported on the breakdown, under lightning and switching impulses, of a concentric electrode arrangement in which the inter-electrode space is spanned either by an insulator surface or by air. Temperature in the system has been varied in the range 10m, where 0.81.0 for negative polarity at the highly stressed electrode. Variations are the same, in the presence or absence of the insulator surface, but absolute positive flashover voltages are lower across the surface, than in air, while negative flashover voltages are higher. Times to breakdown decrease with increasing temperature     

空间电荷对SF_6气体正雷电冲击击穿的作用

利用两种实验方法对比测试了预注入单极性空间电荷时,SF_6气体极不均匀场间隙正雷电冲击击穿特性。分析表明;直流叠加冲击电压法不适用于观察空间电荷的作用,而切换直流/冲击电压法能有效地反映空间电荷对冲击击穿的作用。     

Streamer propagation and breakdown under ac voltage in very largeoil gaps

This paper presents a study of prebreakdown and breakdown phenomena under ac voltage in mineral oil in very large gaps (⩽80 cm). The investigations presented concern the measurement of breakdown voltages together with the recording of streamers in rod-plane and sphere-plane electrode systems, at different gap sizes. A breakdown mode specific to ac voltage is found, in which `bursts' composed of streamers initiated at each half cycle appear. This mode leads to the lowest breakdown fields recorded under ac. Values of the average stress required for burst or direct breakdown modes are deduced from the experiments. Positive streamers are responsible for breakdown in large gaps: their propagation is easy and does not depend on the gap geometry and on the presence of particles. On the other hand, the propagation of negative streamers is quenched when not very divergent fields are used