Bipolar DC corona discharge from a floating filamentary metalparticle

The motion of a filamentary particle and also the discharge from a particle have been extensively investigated for the development of a prevention and protection method against breakdown in gas-insulated switchgear. The particle showed several different patterns of motion, e.g., "standing," precession motion, oscillating up and down, etc. Each of these types of motion depends on corona discharge from the particle itself. Since this motion cannot be explained only by monopolar discharge from one end of a particle, bipolar discharge from both ends of a particle occurring simultaneously has been investigated by applying the floating particle method. The particle length and the gap between the particle and electrode were chosen as parameters. From experimental results, several interesting features were obtained. The curve of bipolar corona. current lies between negative and positive corona currents of monopolar curves. There is a sudden current increase at the threshold voltage that seems to be a new feature of the corona current from a filamentary particle. So far, the experimental results indicate that this threshold voltage is not a function of particle length, but it could depend slightly on length. Flashover voltage is a function of particle length and the gap. It decreases with length and increases with the gap     

Particle-initiated breakdown in a quasi-uniform field intransformer oil

The breakdown voltage induced by single metallic cylinders of millimeter lengths in a quasi-uniform AC field are reported. A particular electrode arrangement, including forced oil circulation, has been designed in order to avoid particle ejection out of the gap. Breakdown occurred in the range 25 to 80 kV/cm depending on the particle dimensions, and always when the particle was in contact with the positive electrode. These breakdown levels are clearly lower than those measured with a fixed particle subjected to a positive step voltage. All these measurements were sensitive to the influence of carbon contaminants, especially under step impulse voltage. As concerns free particles, the breakdown is thought to be controlled in our experimental conditions by the initiation of positive streamers. Calculations showed that the initiation field at the particle tip is not constant but mainly depends on the particle diameter     

DC corona discharge from a wire particle floated with a microgap in parallel plate electrodes

Conductive particles existing in a high-voltage system could deteriorate the system performance owing to an electric discharge via the particles. In case when the particles exist in a dc high-voltage electrode system, the location of the particle would inevitably affect the discharge aspect. A corona-onset and breakdown voltage from a metallic wire particle were measured in detail. The wire particle has a length ranging from 6 to 12 mm, and a diameter of 0.25 mm. It was fixed between a parallel plate electrode with a spacing of 20 or 30 mm. When the particle was close to the negative electrode, a corona discharge occurred stably, and the corona-onset voltage was increased as the gap length between the negative electrode, and the positive end of the particle increased up to 0.8 mm. In contrast, when the particle was close to the positive electrode, the breakdown always occurred without preceding the corona discharge. At the middle region between the electrodes, the corona onset occurred at almost constant voltage.     

AC particle-triggered corona discharge in low pressure SF/sub 6/ gas

This paper deals with AC particle-triggered corona discharge as a follow-up to our previous research with DC voltage to clarify the particle-triggered corona discharge process in SF₆ gas. Corona current pulses, charges associated with a corona current pulse, and corona light pulses were observed with an aluminum ellipsoidal particle suspended in a parallel plane electrode system under a SF₆ gas pressure range of 30 kPalesPles50 kPa by changing the particle position. Corona mode, phase (Phi)-charge (q) characteristics as well as corona discharge processes were discussed and the following results were obtained. AC corona mode depended on the instantaneous applied voltage, voltage gradient as well as the particle position and then, the Phi-q characteristics were also affected by those parameters. Charges flow into the floating particle due to coronas on the both tips of particle and excite field fluctuations around the opposite side of particle in addition to the applied AC field. The field fluctuation in SF₆ gas by the corona charges was about 4% of the applied field and much lower than that in air gap which was about 70%. That is, the corona development was suppressed effectively by high electron affinity of SF₆ gas even in the case of floating particle. The less effective interference between coronas on the both side of particle in SF₆ gas results in an obscure local minimum in the breakdown voltage characteristics as the particle is in the vicinity of electrode as contrasted with a drastic fall in the breakdown voltage by the particle in air     

Gaseous electrical discharge characteristics in air and nitrogen at cryogenic temperature

In designing superconducting electrical power apparatus, the knowledge of cryogenic gas and liquid insulation characteristics is essential. The authors have studied the discharge characteristics of relatively long-gap configurations in air and nitrogen at a cryogenic temperature. A sphere-to-sphere electrode with a gap length of 20 to 150 mm is used for measurements in uniform electric field. The breakdown voltage characteristics basically obey Paschen's law at cryogenic temperature for 50 Hz, AC, DC and lightning impulse voltage applications. A rod-to-plane electrode with a gap length of 20 to 330 mm is used for measurements in nonuniform electric field. In air at cryogenic temperature and nitrogen gas at both room and cryogenic temperature, streamer-like corona discharge appears near the tip of the rod electrode before the breakdown, and the breakdown voltage increases linearly with gap length. In air at room temperature thin film-like corona discharge, however, appears near the tip of the rod electrode before breakdown, and the breakdown voltage becomes higher than the other case. In order to examine the variation of corona discharge characteristics, some additional experiments are conducted. As a result, it becomes clear that thin film-like glow corona discharge appears when electronegative gas is contained and sufficient electrons are supplied from the cathode.     

Particle-triggered pre-breakdown phenomena in atmospheric air gap under AC voltage

Corona discharge mechanism and breakdown voltage characteristics of air gaps in the presence of metallic particles were investigated including the relationship between the corona discharge mechanism and the phase resolved partial discharge patterns. These results are of interest for detection of foreign particles in gas insulated systems (GIS). The results with different shaped particles show that the corona mechanism depends on the particle shape and applied voltage. Moreover the corona discharges on both sides of the particle interfere with each other by inflow of charge carriers into the particle. The breakdown voltage is a minimum when the particle is in the vicinity of the electrode due to active interference of coronas. The phase-charge characteristics as the phase resolved partial discharge patterns vary with the particle shape. This suggests that the corona discharge mechanisms for all types of particles should be considered in the particle-detection method for GIS based on the phase resolved partial discharge patterns.     

Corona and breakdown characteristics between sphere electrode with a protrusion and plane electrode under negative pulse voltage in N/sub 2/ gas

Corona and breakdown characteristics for a configuration of a sphere with a needle and a plane in N/sub 2/ gas are studied. The protrusion was used to simulate a metallic particle attached to a high voltage conductor surface in power apparatus. The corona and breakdown characteristics depend on the vertical distance between the needle tip and the bottom sphere. It was observed that the breakdown path changed from needle-to-plane to sphere-to-plane while increasing the vertical distance of the needle from the plane. Although corona was generated at the needle-tip at first and developed in the direction of the plane, both the needle-plane and the sphere-plane breakdown occurred at some short vertical distances. The sphere-plane breakdown in that distance was triggered by corona from the needle.     

新型双极电晕放电器的放电特性

为了得到放电参数更好的电晕放电器,解决传统电晕放电器在施加单极性高压电源时只在高压电极上放电,而接地极上并不放电的情况,采用了一种新型针—针式结构的双极电晕放电器,在施加单极性高压电源时,放电器内能同时在高压电极和接地电极产生正、负两种不同极性的电晕放电。实验研究直流高压与脉冲高压下新型双极电晕放电器的伏安特性、放电现象和离子风时,在平均场强约3.4kV/cm条件下采用粒子图像测速仪(PIV)测得电场内正、负离子风的核心区风速约2m/s。与针—板式电晕放电器相比,新型双极电晕放电器的工作电压降低,而输出功率和电流密度明显提高。     

电晕放电若干特性的探讨

在较大分子的气体(如SF_6)中,正、负电晕起始电压有明显差别,而且随着气体压强增加而增大。而在较小分子的气体(如空气)中,正、负电晕起始电压基本相同。不仅Trichel(负电晕)脉冲是有规律的,在较低气压下的SF_6气体中,正电晕脉冲也是有规律的。电晕稳定效应不仅受气压影响,而且受尖端半径的影响。对于空气中的正电晕,当尖端半径很小时,击穿电压并不升高。     

Metallic particle movement, corona, and breakdown in compressed gasinsulated transmission line systems

A simplified computational algorithm has been developed to study the behavior of metallic particles in gas insulated transmission line (GITL) systems. The model provides an estimate of the effectiveness of particle trapping for a particular trap design at a given commissioning voltage. Results of measured breakdown probabilities of particle contaminated SF₆ show fair agreement with calculated values. A computational model was developed to calculate the corona inception voltage due to conducting particle motion in GITL systems. The computed results for various parameters were in fair agreement with the measured values. A corona pulse pattern is computed and plotted using the same algorithm. Oscillographic records of the transient corona show that particle discharge is larger for long particles, and its magnitude increases with voltage level. Corona patterns obtained in the laboratory indicate that conducting particles can be detected in GITL systems and that the particle size can be determined through partial discharge measurements with AC voltage at different gas pressures     

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.     

直流电晕电流时域脉冲特性的统计分析

为了研究直流正负电晕电流时域脉冲的特性,基于实验室开发的高频电晕电流高压端测量系统,开展了不同条件下直流正负电晕的线板放电实验。基于大量实验数据,统计、对比了正、负极性电晕脉冲的幅值、上升时间、半波时间和重复频率等特征参数随导线电压及导线半径变化的规律。实验结果表明：导线电压对单个正、负脉冲波形的影响较小,主要影响脉冲的重复频率;负脉冲的上升时间平均值为20~30 ns,半波时间的平均值为90~110 ns;正脉冲的上升时间平均值为40~50 ns,半波时间的平均值为140~160 ns;随着导线电压的升高,正、负脉冲重复频率均迅速增大,但相同电压下,正脉冲的重复频率显著小于负脉冲的重复频率,负脉冲重复频率约为正脉冲的15~25倍。     

静态模拟气固两相体起晕和击穿的实验研究

研究了非均匀电场中的静态模拟气固两相体放电的击穿、起晕特性及固相物介电常数、占空比、放电间隙、电压极性和种类对击穿电压与起晕电压的影响。结果表明:实验范围内,正极性大占空比时,随放电间隙的增加,两相体的起晕电压逐渐低于空气的起晕电压。正极性和交流电压下,两相体的击穿电压比空气高。     

The Sparking Characteristics of Needle-To-Plane Coronas

The sparking voltage (Vs) and maximum presparking corona current (Imax) of needle-to-plane coronas have been measured as independent functions of polarity, tip radius (r), and needle-to-plane spacing (S). For a negative needle, Vs and Imax increase with S but are independent of r. For positive polarity, Vs and Imax increase with both S and r. Thus to increase the corona current while avoiding a spark, one should increase the spacing and voltage. At large spacings, Imax is appreciably greater for negative polarity than for positive. Analysis of the data reveals that for negative polarity the maximum presparking current may be written in the approximate form Imax?Vs(Vs-VO)S-2 where VO is the corona threshold voltage. This is an extrapolation of a relationship previously obtained for Trichel pulse corona. The analysis shows that the transition from negative corona to sparking occurs when the linear space charge density in the gap reaches a critical value Qs/S ?10-10 coul/mm, where Qs is the total space charge in the gap just before sparking occurs. It is shown that this condition amounts to spatial overlap of the multiple ion clouds in the gap, thereby creating a continuous ionized channel between the electrodes.     

邻近直流导线时交流电晕电流脉冲特性试验

本文搭建交直流并行线路电晕放电试验平台,研究邻近直流电压时交流单点电晕放电下的电晕电流脉冲特性。并对交流电晕电流脉冲的分布模式、重复频率以及波形等特征参数进行统计分析。试验结果表明,邻近的正极性直流电压会促进交流负半周电晕放电而抑制交流正半周电晕放电,邻近的负极性直流电压作用正好相反。直流电压对交流负半周电晕电流脉冲波形参数无明显影响,而正半周电晕电流脉冲的幅值会随负极性直流电压的增加有所升高。同时发现,随着交流电压幅值的升高,促使其正半周发生电晕放电所需要的负极性直流电压幅值也相应地升高,并基于电晕放电的发展过程中电离强度的计算提出种子电子的缺失是造成该现象的原因。最后,在电晕放电离子云模型基础上,提出脉冲序列发展的过程中电离区域电场强度恒定不变的假设,从而对邻近直流电压影响下的交流电晕电流脉冲波形参数特性给出了合理的解释。     

气固两相体直流电晕放电特性实验研究

为了研究两相体放电的基础问题,即放电特点、规律及影响因素,实验研究了聚丙烯、聚乙烯、珍珠岩3种典型固体颗粒的气固两相体电晕放电伏安特性。通过循环落体式两相体放电装置和测量系统观察发现,气固两相体的电晕电流特性与空气中的电晕电流特性有明显的区别。气固两相体的电晕电流波形在正、负极性下均为高频率脉冲波形。且在相同电压下其电晕电流比空气中的要小。固体颗粒的介电常数及在空气中所占的体积比均对电晕电流有很明显的影响。固体颗粒介电常数和体积比越大,电晕电流越小(可<1μA)。电压极性的改变对气固两相体的电晕电流无影响。     

Induction of Waves on a Horizontal Water Film by an Impinging Corona Wind

The electric wind produced by corona discharge of a high-voltage electrode in air is employed for destabilizing a horizontal water film. In wire-to-plane geometry, the phenomenon is characterised by current versus voltage curves and visual observations of the onset of free-surface oscillations. The effect of the following parameters is examined for both positive and negative coronas: distance between the wire and the film (S), film thickness (h), wire diameter (phi) and composition, applied voltage (HV), and relative humidity (RH). The free-surface destabilisation is retarded by increasing d and phi and is insensitive to h in the tested range. The onset of corona discharge is predicted by Peek's law and compared with the experimentally observed threshold. In negative corona discharge, the current values are higher and the film is destabilised at lower HV than in positive polarity. Humidity tends to decrease the corona current at a given HV. Correlations are proposed for the current-voltage curves, in terms of the mean electric field in the inter-electrode gap and of RH, satisfactorily agreeing with the experimental data. Both positive and negative corona currents turn out to be stable for days of operation. The power loss by corona discharge is in any case lower than 12 W. Wave induction on the liquid-gas interface can effectively enhance heat and mass exchange between the two phases.     

尖端导体电晕放电辐射场的计算与实验

为研究输电线电磁辐射问题,以尖端导体电晕放电为研究对象,利用偶极子模型和传输线模型尖端导体电晕放电辐射场进行理论计算,得出了电磁辐射信号特征;在实验室进行直流高压下尖端电晕放电模拟和实验研究,验证了理论分析的正确性。研究结果表明,电流注入导体产生的辐射场要比空气电晕区产生的辐射场强的多,在对尖端导体电晕放电辐射场的远距离探测时,空气电晕区产生的辐射场可以忽略不计;尖端导体电晕放电辐射场主要是垂直极化场,由电晕电流在导体两端来回反射引起的;信号的时域波形呈衰减振荡形式,信号的峰值随外加电压的升高而增大,正电压下信号的强度明显比负电压下信号的强度大;信号首脉冲的方向随外加电压的极性不同而相反;信号的持续时间在几百ns数量级,而且随着导体长度的增加,信号的持续时间有增大的趋势。该研究结果对于输电线电晕抑制及周围电磁环境评价具有重要意义。     

Dielectric breakdown characteristics of cryogenic nitrogen gasabove liquid nitrogen

We measured the DC dielectric breakdown characteristics of cryogenic nitrogen gas above a liquid nitrogen surface for needle-to-plane and sphere-to-plane electrode configurations. Experimental results revealed that the DC breakdown voltage of cryogenic nitrogen gas increased, as the distance from the gap axis to the liquid nitrogen surface diminished, i.e. as the liquid nitrogen surface got closer to the gap. The breakdown voltage proved to be enhanced not only by the temperature drop of nitrogen gas due to the existence of liquid nitrogen, but also by an effect of vapor mist arising from vaporization of liquid nitrogen. For the quasi-uniform electrode configuration, the relation between breakdown voltage and the gas density times the gap spacing agreed well with the Paschen curve for nitrogen with both the temperature falling and the vapor-mist density considered. For the nonuniform needle electrode, positive breakdown voltage was higher than negative one; the polarity effect was interpreted in terms of the electric field relaxation at the tip of the positive needle resulting from partial discharges observed only for the positive needle     

多针电极结构双极电晕放电伏安特性

为提高电晕放电的能量密度和放电稳定性,提出了针阵列电极结构的双极电晕放电方式并研究了多针电极结构双极电晕放电的伏安特性。实验得出放电电流I随针尖半径a和电极间距d的增大而减小,随相邻针尖间距s的增大而增大,但当s≥40 mm时,相邻针尖的相互作用已很小,I几乎不变;d对火花击穿电压的影响较大,a对其的影响较小。由于电极结构的对称性,高压电极的极性对放电无明显的影响,正负电晕放电的伏安曲线和火花击穿电压均较为接近。将多针电极双极电晕放电电流I等效成电极间距为d/2的多针对板正、负电晕放电电流I1和I2相加,分析了I>I1+I2的原因,并推知其电离区内电子密度也有相应规律。