Impulse insulation characteristics of a composite insulation system having a wedge gap in SF6 gas

Impulse insulation characteristics were investigated in a composite insulation system having a wedge gap in SF₆ gas. The partial discharge inception voltages of wedge gaps with various types of film were measured and compared with the calculated breakdown voltages estimated from Paschen's curve of SF₆ gas. Also discussed is how the charge accumulated on the film surface due to a partial discharge had an effect on the creepage breakdown voltage. Partial discharge inception voltages in wedge gaps were higher with higher SF₆ gas pressures and with lower film permittivities. Creepage breakdown voltages depended little on gas pressures or on creepage distances. The dependency of breakdown voltages on gas pressures and the effect of polarity on the breakdown voltage differed with the types of film. This may be partly because the charge on the film due to partial discharge had an effect on the discharge propagation, and that charging of the film differed with the types of film.     

PD time‐sequential properties of SF6 and SF6 gas mixture including CO2

This paper deals with partial discharge (PD) time‐sequential properties of SF₆/N₂/CO₂ ternary gas mixture as well as SF₆ and SF₆/N₂ gas mixture under AC and positive DC voltage applications. The measurements were carried out by changing the gas pressure up to 0.6 MPa and applied voltage with the N‐shape characteristics of breakdown voltage versus gas pressure for each tested gas considered. We obtained experimental results of the gas pressure dependence of maximum peak value of PD current pulse as well as the relationship between the time interval of PD pulses and the peak value of PD pulse. We discuss the mechanism of increase in breakdown voltage by adding CO₂ into SF₆/N₂ gas mixtures in terms of change of PD type from streamer to leader discharge. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 151(3): 32–40, 2005; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20073     

Insulation properties of a CO2/N2 50% SF6 gas mixture in a nonuniform field

This paper describes partial discharge (PD) inception and breakdown voltage characteristics of a CO₂/N₂/SF₆ gas mixture in a nonuniform field. These voltage characteristics were investigated with ac high voltage by changing the mixture rate of each gas of CO₂, N₂, and SF₆ gas and the gas pressure from 0.1 MPa to 0.6 MPa. It was found that adding a small amount of CO₂ gas into a N₂/SF₆ mixture causes a drastic increase in the breakdown voltage. For instance, when the mixture rate of SF₆ in N₂/SF₆ gas mixture is 50%, with the addition of 1% CO₂ the maximum breakdown voltage becomes 1.31 and 1.15 times higher than that of a 50% N₂/50% SF₆ gas mixture and pure SF₆ gas, respectively. Moreover, those voltage characteristics of a CO₂/N₂/SF₆ gas mixture were also investigated by changing the electric field utilization factor as well as by applying positive and negative standard lightning impulse voltages in order to discuss the corona stabilization effect, which seems to be one reason for the drastic increase in the breakdown voltage. These results and breakdown mechanism of the CO₂/N₂/SF₆ gas mixture are discussed on the basis of the corona stabilization effect and the dissociation energies of the component gases by observing PD light images, PD light intensities through a blue and red filter, and PD current waveforms. © 2002 Wiley Periodicals, Inc. Electr Eng Jpn, 140(3): 34–43, 2002; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10019     

Impulse partial discharge and breakdown characteristics of rod–plane gaps in air and N2 gases

In response to growing environmental concerns, we attempted to develop switchgear without using SF₆ gas. In our research, we used compressed air and pure N₂ as an electrical insulation gas, because of their low global warming potential. In this paper, we examined the impulse breakdown and impulse partial discharge characteristics under various conditions related to nonuniformity of the electric field. The experimental results show that the breakdown voltage (BDV) of air is higher than that of pure N₂ gas under highly nonuniform field conditions in the rod–plane gap. On the other hand, the discharge inception voltage of air and N₂ were almost the same. Furthermore, first partial discharge (PD), leader discharge, and its transition to the breakdown were successfully observed through the measurement of discharge current and light emissions under impulse voltage application. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(3): 36–43, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10277     

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     

A study on condition assessment method of gas‐insulated switchgear. part II. influence of moisture in the SF6, detection of a partial discharge on a spacer,repetition discharge and overheating by incomplete contact

Rationalization of the maintenance of gas‐insulated equipment under operation and lifetime extension based on the results of appropriate diagnosis are necessary to reduce the cost of gas‐insulated equipment. Therefore, condition‐based maintenance (CBM) is required and accurate methods for observing the inside of equipment are important. In this report, we describe a diagnosis method that can be used for actual gas‐insulated equipment, such as to assess the deterioration of the spacers made of epoxy resin and to detect loose connections in the central conductor. The principal results are summarized as follows: (1) The quantity of decomposition gases depends on the moisture and magnitude of the partial discharge. However, decomposition gases were detected even if SF₆ had low moisture content (less than 100 ppm) similar to that used in actual equipment. This means that our method can be applied to actual equipment. (2) It became clear that CF₄ is a typical gas generated by partial discharge on the spacer surface. Therefore, it is possible to diagnose spacer deterioration by monitoring CF₄. (3) Decomposition gases (SF₄, SO₂, SO₄, SO₂F₂) were generated by impulse breakdown, which was assumed to be due to repetition discharge caused by insulation failure and loose connections. (4) SF₆ gas was assumed to be exposed to a loose connection and was heated from room temperature to 800 °C, and the generated decomposition gases were analyzed by FTIR in real time. As a result, the decomposition gases were generated at temperatures above approximately 500 °C in a heating time of 1.5 minutes. Therefore, a loose connection can be detected by analyzing the decomposition gas. © 2011 Wiley Periodicals, Inc. Electr Eng Jpn, 176(2): 22–30, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21108     

工频恒定电压下SF6气体中沿面放电发展过程研究

气体绝缘组合电器(GIS)中绝缘缺陷的存在会造成局部放电,导致设备劣化,进而危害到电力系统的稳定性。其中危害较严重的为绝缘子沿面放电缺陷,为探究其在工频恒定电压作用下的放电发展过程及规律,文中制作了“三结合”模型模拟SF 6中沿面放电缺陷并展开试验。保持工频电压在模型闪络电压的95%不变,每隔5 min记录一次局部放电信号,直至模型频繁发生闪络,分析各阶段放电统计参量的变化。结果表明沿面模型在闪络前的放电呈现放电重复率增加、放电量增加、放电间歇、放电再次增强的发展过程。放电间歇的产生与SF 6的强电负性、电场均匀化等均有一定关系。因此,需通过长时间放电检测以准确判定设备劣化阶段,并采取相应措施。     

SF6压力对GIS典型缺陷局部放电检测灵敏度的影响

气体绝缘开关设备(gas insulated switchgear,GIS)内部气压是影响局部放电检测灵敏度的重要因素。在局部放电实验平台中构建尖端、悬浮、气隙与沿面缺陷模型,基于特高频法、高频电流法与超声法开展气压0.2~0.5 MPa下局部放电信号特征的检测实验,并对比了高频电流法和超声法局部放电检测的灵敏度。实验结果表明：气压是影响尖端、悬浮与沿面缺陷放电的关键参数,3种缺陷放电起始电压与气压成正比,同一电压下的放电幅值和脉冲次数与气压成反比;气隙缺陷放电源于绝缘层内部气泡,因此设备气压对气隙缺陷放电影响不大。高频电流法可实现不同气压下的悬浮缺陷有效检测,但未测得气隙和尖端缺陷局部放电信号;SF₆压力降低,高频电流对沿面缺陷的检测灵敏度有所提升,但仍低于特高频法。超声法可实现不同气压下的悬浮和尖端缺陷有效检测,但未测得气隙和沿面缺陷局部放电信号;SF₆压力降低,超声法对尖端缺陷的检测灵敏度提高(当气压为0.2 MPa时,超声法对尖端缺陷的检测灵敏度与特高频法相当)。     

振荡冲击电压下典型绝缘模型局部放电解析(英文)

The aim of this paper was to give an overview on partial discharges under oscillating impulse voltage.Three models(void in solid,needle-plate in air and oil) were presented,which describe the stochastic discharge process and represent internal discharges in solids and corona in air or silicon oil.Moreover,an air cored Rogowski coil and a sampling resistor for partial discharge(PD) measurement were developed and introduced in this paper.PD inception and extinction voltages(PDIV,PDEV) under single oscillating impulse voltage and AC voltage were investigated with different test samples.Experimental results firstly revealed that the PD inception voltage(PDIV) decreased with increasing applied voltage;secondly the PD inception voltage for three different insulating materials,showed an escalating trend with increasing frequency of the applied voltage.It was proven that the characteristics of PD under oscillating impulse voltage were identical to the features under AC voltage,which could be measured with the phase resolved partial discharge analysis(PRPDA) technique.Based on the reorganization and analysis of PDs under oscillating impulse voltage,the information about insulation defects was extracted from the measured data and used for estimating the risk of insulation failure of the equipment.     

Study on decomposition gas for diagnostics of gas‐insulated transformers

Concentrations of population and business activities result in high energy demand in urban areas. This requires the construction of underground substations. Oil‐free, nonflammable, nonexplosive equipment is recommended for underground substations. For this reason, gas‐insulated transformers have been developed. A diagnostic method for gas‐insulated transformers is thus required. This paper provides an experimental survey of the main components of decomposition gas generated by various faults in gas‐insulated transformers carried out through simplified model tests. The phenomena of overheating and partial discharges are modeled, taking the actual materials related to each fault into account. For example, CO, CO₂, and aldehydes are produced by overheating of pressboards and PET films. The amount of gas produced increases with rising temperature. While various gases are produced from a partial discharge, the principal components are SO₂ and SOF₂. These results will be used to develop a diagnostic method for gas‐insulated transformers. © 1999 Scripta Technica, Electr Eng Jpn, 130(1): 48–58, 2000     

Investigation of partial discharge mechanism by simultaneous measurement of current waveform and light emission

We observed current pulse waveforms of partial discharge (PD) in SF₆ gas so as to investigate the PD mechanism. We also measured light intensity and light emission image of PD simultaneously under different conditions of applies voltage and SF₆ gas pressure. From these experiments, we found that the “double-peak current waveform” appeared at high pressure and high voltage conditions. We also analyzed the mutual correlation of waveforms between a single current and the light emission. Moreover, we obtained experimental evidence of filmentlike light image appearing at the PD tip under the same condition with double-peak current waveform. From the electric field analysis around the needle electrode tip, we believe that the filamentlike light image expands beyond the critical electric field of SF₆ gas. Thus, we concluded that these current waveforms with double peaks showed evidence of leader-type PD, leading to breakdown. Finally, we could point out that leader-type PD should be distinguished and measured for the diagnosis of GIS insulation performance. © 1999 Scripta Technica, Electr Eng Jpn, 129(4): 58–65, 1999     

Effects of a barrier on creeping discharge characteristics in SF6 and N2 gases under pulse voltages

This paper describes the effect of a barrier on creeping discharge characteristics in SF₆, N₂, and their mixtures. The barrier height effect on the discharge voltage was investigated under a positive pulse voltage. The discharge voltage increased with increasing barrier height in SF₆ gas. On the other hand, the discharge voltage hardly changed with the barrier height in N₂ gas. In order to clarify the mechanism of the initial creeping corona, it was observed by optical techniques, including an ultra-high-speed electronic imaging system (IMACON 468). The creeping corona path revealed differences in images at various barrier heights. The accumulated charge induced on the barrier by the initial corona in SF₆ gas was able to suppress the development of the later creeping corona, in contrast with N₂ gas. © 1998 Scripta Technica, Electr Eng Jpn, 125(4): 1–8, 1998     

利用局部放电评价GIS典型缺陷危险性的研究

采用脉冲电流法测量局部放电PRPD谱图,4054示波器获取局部放电信号的脉冲波形,研究了针板缺陷不同间隙距离下局放的起始电压、击穿电压和放电量;针板缺陷从发生局部放电到击穿整个过程PRPD谱图、放电脉冲的变化情况。研究结果表明,间隙距离越小,针板间隙发生局部放电后越危险;局部放电从产生到击穿可分为3个阶段,即放电起始阶段、放电发展阶段和邻近击穿阶段,以上结果为利用局部放电判断GIS运行状态提供了有效的判据。     

Creeping flashover characteristics in (N2/SF6) gas mixture under pulse voltage

The effect of a barrier between a needle electrode and a plane one in an (N₂/SF₆) gas mixture on creeping flashover was investigated using a microsecond pulse voltage. The SF₆ gas content was varied from 0% to 100%, and the gas pressure from 0.1 MPa to 0.3 MPa. The flashover voltage increased with increasing SF₆ gas content for a positive needle electrode. For a negative needle electrode, excepting the total pressure of 0.1 MPa, at which similar flashover characteristics were obtained to the positive case, a considerable decrease in flashover voltage was found in the case of a mixture of a few percent SF₆ in (N₂/SF₆) gas mixture at elevated total pressures. The corona behavior on the barrier in (N₂/SF₆) gas mixture was investigated by means of a high‐speed digital framing camera. © 2000 Scripta Technica, Electr Eng Jpn, 131(1): 1–9, 2000     

Effect of lightning impulse prestress on AC partial discharge characteristics in cast resin transformer

It is crucial for cast resin transformer to detect void and delamination existing in the cast resin because these defects reduce insulation performance of cast resin equipment. Furthermore, defects are likely to be mixed in cast resin because of several surface boundaries between resin and conductor. It is considered that detecting partial discharge (PD) is effective to diagnose equipment of power equipment. However, it is reported that withstand lightning impulse voltage test may give influence on AC partial discharge test, especially partial discharge inception voltage. This paper deals with accumulated charge in a void under AC voltage to investigate the effect of the impulse voltage prestress on subsequent AC PD characteristics in cast resin transformer. AC PD characteristics were compared before and after impulse application. In addition, recovery of PD characteristics was measured to investigate charge decay. As a result, the mechanism of prestress effect is revealed and surface charge density is estimated quantitatively in cast resin transformer.     

750 kV变压器现场工频感应耐压和局部放电试验

介绍了我国750 kV输变电示范工程中变压器现场局放交接试验的标准、程序和过程，分析了局放起始电压和熄灭电压定义中的含混之处，比较了750 kV变压器的工频耐压值和局放试验电压值、分析了局放试验中经常出现的问题。提出如下建议：①提高750 kV变压器的工频绝缘水平；②放宽变压器局放现场交接试验标准至1 000 pC；③重新定义局部放电起始电压和熄灭电压；④加强现场实用技术的研究；⑤试验人员持证上岗；⑥试验仪器定期校验；⑦必要时采用在线监测。这些建议不限于750 kV变压器，也可为 1 000 kV变压器的现场局放交接试验参考。     

方波脉冲电压频率对变频牵引电机绞线对绝缘特性的影响

测试了不同频率方波脉冲电压下牵引电机绞线对的电热联合老化寿命、介质损耗因数（tanδ）及局部放电平均放电量,测试结果表明：方波脉冲电压频率升高,使局部放电平均放电量增大,局部放电对绞线对绝缘的破坏作用加强,使绞线对的老化寿命缩短;方波脉冲电压频率升高,使绞线对老化程度加深,陷阱密度增大,降低了自由载流子浓度,使局部放电起始放电电压（PDIV）增大,从而使介质损耗因数曲线转折点电压升高.     

直流局部放电检测技术综述

局部放电检测技术作为一种重要的绝缘性能评估手段,在交流电气设备的绝缘检测领域发挥了重要作用,而直流局部放电检测研究尚处于初级阶段。由于直流局部放电相比交流没有相角概念,交流下常用的局部放电分析手段无法直接套用于直流当中。综述了国内外直流局部放电检测的研究现状,介绍了直流局部放电的物理模型以及温度等因素对局部放电的影响机理,总结了目前国内外直流局部放电研究常用的分析方法,并对直流电缆局部放电测试的典型案例进行了分析。     

电机绝缘系统在高频冲击下局部放电试验研究

高频冲击局部放电(PD)测试可以有效的检测电机绝缘系统的绝缘状态。根据传感器的不同,电机绝缘系统在高频冲击下PD测试方法主要有两种:高频电流传感器法和超高频天线法。试验表明:在高频冲击电压下,PD主要发生在冲击的上升沿和下降沿,在同一放电电压下,上升沿和下降沿的PD幅值较大;在风力发电机定子绝缘系统鉴别试验中,随着老化试验的进行,线圈的PD起始电压总体呈下降趋势。通过鉴别试验,可以确定绝缘系统的冲击电压绝缘等级及类型。     

Characteristics of creeping discharge developed in a narrow gap between insulators and effect of a backside electrode

Discharge characteristics have been investigated for a needle–plane electrode configuration containing insulating barriers with a narrow gap which has been placed between the needle and the plane. The characteristics of creeping discharge developed in the narrow gap of the barrier filled with SF₆ are especially considered. In the case of a configuration with a backside electrode below the needle, the corona generated from the needle easily extended to the gap. On the other hand, for a configuration without a backside electrode, the corona has hardly extended to the gap, and on increasing the applied voltage the corona developed greatly in the gap. This difference in corona extension should affect the flashover characteristics in the present system. © 2003 Wiley Periodicals, Inc. Electr Eng Jpn, 146(2): 27–36, 2004; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.10248