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.     

交直流复合电压下电晕放电实验研究(英文)

Converter transformers are one of the most important electrical apparatuses in the ultra high voltage(UHV) DC transmission systems.The valve side and the low voltage(LV) bushing are stressed by long-term AC and DC composite voltage leading to significant partial discharge(PD) and posing great danger to the insulation system.In this paper AC and DC composite voltage is applied on a metal needle-plate model to produce PD signal sequences,and then the pulse waveshape and frequency spectrum are analyzed and compared with PD signals under conventional AC or DC voltage.In the end,the phase-resolved distribution is analyzed to depict the new characteristics of PD under this composite voltage.     

绝缘电极之间雷电冲击下油中放电特性分析(英文)

Looking at the problem of electrical discharge development in mineral oil, it is easy to see that most studies in this area focused on the setups of bare high voltage electrodes having a point-plane electrode arrangement. The setups with insulated electrodes are the mar- gin of these studies but it seems to be important to find the dependences between the paper insulation on high voltage electrode and parameters of the discharges initiated in the vicinity of this electrode. Hence, in this paper the results of researches intended to reveal the role of insulation wrapping on a HV electrode in the mechanism of electrical discharges in transformer oil under lightning impulse of both polar- ities are presented. This role is determined by analysis of the parameters characterizing the discharges (onset voltage, propagation velocity, time to initiation, rise-time of light impulses) and also by observation of their spatio-temporal development and oscillograms of the light emitted by their channels. The research was performed for two model electrode configurations: an electrode with paper insulation and a bare electrode which had the same outer dimensions as the insulated one. The most essential conclusion from performed experiment is related to times to initiation. These times, equal in the case of insulated electrodes and model bare electrode, indicate that the source of "weak points" of the paper-oil insulation system is the oil, not the surface of insulation wrapping or the metal.     

电晕放电脉冲电流波形和相位分布的测量、分析与仿真(英文)

Partial discharge(PD) is one of the most important phenomenon in high voltage insulations.In most cases, the appearance of partial discharges is related to insulation defects.Understanding partial discharges is important for diagnosis on insulation condition.Corona discharges appear when extremely high electric field appears on the conductor surface exceeding the electric field strength of the gas.The high electric field may occur at around protrusion with very sharp tip.This paper reported a holistic approach of corona discharge investigation.The needle-plane electrode system was used.The medium between the electrodes was air.The needle was made from steel with radius of curvature of 3μm(Ogura needle).Sinusoidal as well as triangular applied voltages were used.The waveform of the corona discharges was measured using a digital oscilloscope.The corona discharge pulses were measured using a phase-resolved PD measurement system.The system was able to measure the magnitude(q) and phase angle position(φ) of each PD pulses,as well as the number of discharge pulses(n).The role of applied voltage was investigated using phase-resolved analysis of corona discharge pulses through pulse sequence,pulse magnitude and pulse number analysis. Experimental results indicated that corona discharge current waveform was an impulse with rise time of about several ns and the impulse width of about 100 ns.The Fast Fourier Transform analysis indicated that the corona discharge current waveform had several spectrum peaks at frequency of 7.8 MHz,85.9 MHz,109.4 MHz and 195.3 MHz.The experimental results also showed that discharge pulses were concentrated around the peak of applied voltage for both sinusoidal and triangular voltages.The discharge magnitude,as well as its probability of occurrence,was strongly dependent on the instantaneous applied voltage.The shape ofφ-n,as well asφ-q-n PD patterns,were strongly reflected by the shape of applied voltage.In order to get deep understanding of the corona discharge,by utilizing results of the phase-resolved analysis,electrical equivalent circuits of corona discharges were proposed.The electrical equivalent circuit contained capacitances and a spark gap.For deeply understanding of PD phenomenon,computer simulation was done by using the proposed electrical equivalent circuits.The similarity of the measured and simulated PD patterns was assessed by comparing measured and simulated theφ-q-n andφ-n PD patterns.The results indicated that simulated PD patterns similar to those obtained from experiment.     

采用Fisher判别法对GIS中局部放电类型的识别(英文)

To monitor the condition of online power apparatus accurately and provide appropriate guidance on their maintenance,a fundamental ultra-high frequency(UHF) database of partial discharges corresponding to different types of defects is presented for the observation of insulation state of gas insulated switchgear(GIS).In order to imitate the defects in a GIS online,five types of typical partial discharge(PD) sources(i.e.floating metal,protrusion,bouncing particles,void in spacer,and particle on the surface of solid insulation) were designed and fabricated.A wideband UHF sensor and an amplifier were applied to obtain UHF signals.Based on the characteristics of the five different defects,nine meaningful parameters which were independent of the phase of the applied voltage were extracted from the PD samples and then discussed.In this paper,Fisher discriminant analysis(FDA),a pattern recognition algorithm,was applied for the purpose of classifying the defects.In this way,there was no need to set complicated parameters and kernel function,and the total discrimination accuracy of test samples was 97.6%.It indicates that based on the nine especial parameters,the typical defects in GIS can be identified exactly by means of FDA.Hence the analysis method could be possibly regarded as a universal classification method.     

电压响应方法在电力变压器状态评估中的应用(英文)

Power transformer is one of the most important equipment in the power system.Its operating condition affects the reliability of power supply directly.Therefore,in order to guarantee transformer operation safely and reliably,it is necessary to assess condition of power transformer accurately.Return voltage method based on voltage response measurements is still a new non-intrusive diagnosis method for internal insulation aging of transformer.In this paper the technique and application of return voltage measurement and some results of voltage response measurements of several transformers was introduced.Voltage response measurements were performed on various transformers with different voltage grades,various operating periods,different moisture contents and aging degrees on site.Derived moisture contents from return voltage measurement were compared with the corresponding moisture contents obtained from the analysis of oil samples.Based on on-site experiments and theoretical analysis,the criteria for insulation state of transformer are proposed.Moisture condition of transformer insulation can be determined by using return dominant time constant,and a good correlation between aging degree and the return voltage initial slopes of the aged transformers.Field test performed on several transformers,its interpretation of results are also presented,which proves that return voltage measurements can be used as a reliable tool for evaluating moisture content in transformer insulation.     

临近高压电气设备电缆局部放电脉冲的鉴别方法

On-line partial discharge(PD)diagnostics data are corrupted by various noise sources and this makes it more challenging to extract the PD signal contained in the raw data.Though the noise sources can be filtered out using signal processing techniques,PDs from neighboring cables and other high voltage equipment make the de-noising process more difficult due to the similar features of these signals with the PD signal of interest.Proposed in this paper is a double-ended partial discharge diagnostic system with dual sensors at each end which uses wireless time triggering using global time reference with the aid of global positioning system(GPS).Using the time of arrival method based on the velocity of propagation on the data,PD pulses originating from other sources can be discarded which reduces the volume of data to be stored and would eventually also reduce the hardware and software requirements of the denoising process thereby improving de-noising efficiency.System design,laboratory tests and on-site measurements are discussed.     

局部放电射频信号与其视在放电量的关联分析(英文)

Radio frequency(RF) measurement has become a hot issue for partial discharge detection.However,its application is hampered by the difficulty to establish a relationship between the RF measurements data and apparent discharge quantity.In this paper,on the basis of an experimental model of metal protrusion,the relationship between the results of RF measurement and pulse current method(IEC 60270) was investigated.The energy,double integration,peak voltage,peak-peak voltage and the area of RF signals were plotted versus either the apparent discharge quantity or the square of the apparent discharge quantity in order to evaluate the optimal regression curve.At the same time,the impact of voltage and the distance between protrusion and plate were also investigated.The results indicate that the optimal match to a linear regression curve can be gained by plotting the RF signal energy versus the square of the apparent discharge quantity.The variation of voltage has no significant impact on the regression curve;that is,data from different voltages match one line.However,when the distance between protrusion and plate is changed,the slope of the regression curve changes accordingly;the same energy corresponds to a bigger discharge quantity.The results are significant enough to be applied in the estimation of the discharge quantity by measuring RF partial discharge signals.     

Online Partial Discharge Measurement of a High-voltage Direct Current Converter Wall-bushingEI北大核心CSCD

An online partial discharge （PD） measurement performed on a high voltage direct current （HVDC） wall bushing successfully identified the presence of internal discharges. The wall bushing is a sulfur hexafluoride gas-insu- lated bushing, rated for 500 kV dc and terminated on a thyristor-controlled HVDC converter bridge. The measure- ment of PD within the HVDC station environment is particularly challenging due to the high levels of electromagnetic noise caused by thyristor switching events and external air-corona from the neighboring high-voltage equipment. An additional challenge is the ＂mixed＂ voltage stress on the bushing insulation, which has both ac and dc high-voltage components. There are also fast transients during the firing of thyristors in the HVDC conversion process that cause added stress to the insulation. As a result, the analysis and interpretation of PD data for HVDC equipment is more complex; PD pulses may occur in response to the ac, dc, or switching transient voltage stresses. In this paper, an on- line PD measurement strategy for noise filtering and isolation of PD sources within the bushing are discussed. The PD measurement data is plotted on a phase-resolved diagram where the line supply power cord voltage was used as a reference. The phase-resolved diagram appears to suggest that the fast transients, caused during switching, trigger some PD events. Measurements were also performed with the aid of a modern PD measurement instrument having noise separation capabilities. The findings from the online PD measurements are verified with physical evidence, found after the bushing was removed from service, suggested internal PD had occurred inside the bushing.     

老化绝缘纸表面的沿面放电试验分析

在故障变压器检修及事故调查中发现,变压器内绝缘纸界面发生沿面闪络后会留下烧灼痕迹,对此分析了油纸绝缘界面沿面闪络的起因及影响因素。测量了在添加和不添加绝缘纸板条件下绝缘油的击穿电压和起始局放电压,分析不同热老化程度的绝缘纸沿面闪络电压和起始局放电压的变化规律。研究结果表明:添加新绝缘纸不会改变油间隙的电气强度,但是老化后的绝缘纸会大幅降低油间隙的沿面闪络电压以及起始局放电压,在老化过程中产生的大量水分子可能是导致上述试验现象的重要原因。     

三元混合式绝缘油与绝缘纸板“液–固”组合体系的沿面闪络特性

油浸式电力变压器中油-纸绝缘体系的"液–固"交界面易发生沿面闪络,导致变压器绝缘失效。为考察新型三元混合式绝缘油对油-纸绝缘体系沿面闪络电压的提升效果,为此以矿物油–纸绝缘为参比,研究了交流电压下三元混合式油–纸绝缘体系的沿面闪络特性,分析了沿面闪络电压、油浸纸板表面损伤、以及沿面闪络后的油中溶解气体特性。结果表明:当针–板电极间距离由5 mm增大至20 mm时,与矿物油–纸绝缘体系相比,三元混合式绝缘油-纸绝缘体系的沿面闪络电压约高10%~20%,主要原因在于三元混合式绝缘油–纸绝缘体系中针电极尖端的电场值较小,且三元混合式绝缘油的击穿性能优于矿物油。经历多次沿面闪络后,三元混合式绝缘油浸渍纸板的表面损伤程度弱于矿物油浸渍纸板,且三元混合式绝缘油中溶解的C2H2及总烃类气体含量低于矿物油。该结果为安全应用三元式混合绝缘油提供了数据支撑。     

直流下油纸绝缘中局部放电脉冲典型波形及其参数提取

笔者介绍了直流下局部放电脉冲波形测量系统的组建以及测量电阻的校验。利用该试验系统对模拟换流变压器油纸绝缘的5种典型缺陷模型进行了局放脉冲波形测量。试验结果表明:直流下油纸绝缘中缺陷放电稳定,脉冲波形无振荡分量和过冲,且不随电压变化而发生畸变。在对典型脉冲波形进行预处理的前提下,使用形状参数法、自相关函数法、AR模型参数法以及Renvi信息量进行了波形特征参数提取。所得结果为深入研究直流下油纸绝缘中局部放电机理、局放在线监测系统的频率特性以及放电类型的波形识别提供了实验依据。     

Application of common transformers faults diagnosis methods on biodegradable oil-filled transformers

Due to environmental concerns regarding the use of mineral oil, biodegradable oil is increasingly being used as an alternative dielectric fluid. This paper presents results of experiments performed in the laboratory on the use of biodegradable oils for transformer application. The investigations cover two important diagnostic techniques for insulation assessment: (i) an investigation of partial discharge (PD) activity and characteristics in such oils and (ii) an investigation of the standard hydrocarbon dissolved gas products produced due to transformer faults. The fundamental aim of the investigation was to provide information as to whether the existing analysis techniques of PD fault pattern recognition and dissolved gas analysis methods, developed for mineral oil, are valid when used for insulation assessment with biodegradable transformer oil. The experiments were conducted on test samples to simulate three common types of transformer faults: low-energy PDs, high-energy arcing/sparking, and overheating. For the purpose of comparison, the same tests were performed using a mineral oil (Shell Diala MX) and a biodegradable oil (Envirotemp FR3). Also, each oil type was tested at three different moisture levels and with or without the presence of solid insulating materials (pressboard). PD activity was monitored using the standard IEC60270 phase-resolved analysis method. The fault gases produced were extracted and analysed by standard gas chromatography methods. Test results indicate that the PD phase resolved patterns are, in general, similar for the two oil types and thus existing PD pattern interpretations can be used to distinguish different types of PD faults, e.g. corona versus surface discharges. However, the values of various discharge quantities (PD magnitudes, repetition rate, current, etc) are very different under the same test condition. The quantities and the trend of dissolved gases for faults in biodegradable oil are substantially different compared with mineral oil. For the PD fault, biodegradable oil was found to release only a limited number of gases. For arcing and overheating faults, the main key gas produced is different between the two oils. Also, the presence of cellulosic materials such as pressboard influences the extent of hydrocarbon gases dissolved in the oil. It was found that for biodegradable oil, fewer amounts of gases are produced as the oil gets wetter.     

基于介电响应的油纸绝缘寿命预测方法

油纸绝缘是油浸式电力变压器的重要组成部分,其绝缘寿命受热老化因素影响很大。因此,针对不同温度、不同含水率下的油浸纸板的寿命预测问题进行分析,提出一种应用平移因子和纤维素反应二阶动力学方程预测不同温度、不同含水率下的油浸纸板寿命的方法。首先,针对不同含水率的油浸纸板进行变温介电谱测试和130℃条件下的加速老化试验;其次,依据频温叠加的基本原理,将所测的介电损耗曲线进行计算平移,得到相应含水率油浸纸板的平移因子,根据平移因子计算相应油浸纸板的活化能,并得出油浸纸板含水率与活化能的关系式,重新构造平移因子表达式;最后,将130℃下测得的老化试验数据和平移因子代入纤维素反应二阶动力学方程,使得该模型可以计算不同温度、不同含水率下的油纸绝缘老化寿命。     

基于局部放电统计参量的脉冲电压下绝缘老化分析

主要针对匝间和对地绝缘电磁线在脉冲电压下老化后的局部放电特征进行了研究.通过不同老化时间的局部放电相位相关分析,在高频脉冲电压下老化后放电次数相位分布出现明显的"放电丛"现象,并通过工频老化后的局部放电结果对此加以证实.通过两种不同电磁线老化特征对比,匝间绝缘和对地绝缘呈现不同的放电特征,匝间主要以内部气隙放电为主,而对地绝缘电磁线则以槽放电为主.此外,测量和分析了局部放电统计参量(如偏斜度、峭度、不对称度等)随老化时间的变化,结果表明平均放电量的偏斜度和老化时间有着一定联系.为更深入地研究脉冲电压下绝缘老化机理打下了坚实的基础.     

A novel technique for partial discharge and breakdown investigation based on current pulse waveform analysis

A novel technique for partial discharge (PD) measurement and analysis (PD-CPWA; PD current pulse waveform analysis) is developed and introduced in this paper. PD-CPWA is expected to be utilized to discuss PD mechanisms and physics in electrical insulating materials, focusing on the PD current pulse waveform and its time transition from PD inception to breakdown (BD). In this paper, the concept and principle of PD-CPWA are described, and the applications of PD-CPWA to (1) epoxy spacer samples under thermal and electric combined stresses in GIS, (2) creepage PD on epoxy spacers in SF/sub 6/ gas and (3) liquid nitrogen/polypropylene laminated paper composite insulation system for high temperature superconducting cables are introduced and discussed.     

绝缘纸板老化对油纸绝缘沿面放电发展规律的影响

为研究绝缘纸板老化对油纸绝缘沿面放电发展规律的影响,采用加热老化方法制备了不同老化程度的绝缘纸板试样,设计了柱板放电模型,采用恒压法对各老化程度绝缘纸板试样进行长时间加压实验,测量并采集了局放信号,统计了不同老化程度绝缘纸板沿面放电各阶段总放电量、最大放电量、放电次数等变化规律,总结了绝缘纸板老化对其沿面放电发展规律的影响。将理论分析与仿真相结合,分析了产生该影响的主要原因。实验结果表明:放电前期,放电主要由处在高场强区的变压器油产生,此时绝缘纸板老化程度对沿面放电总放电量、放电次数、最大放电量等无明显影响;随着放电的发展,绝缘纸板内由老化产生的孔隙中填充的变压器油分解产生气体,加剧了放电程度,此时绝缘纸板老化程度对其沿面放电影响较大,老化程度越高,总放电量、放电次数、最大放电量等增加速度越快,数值也越大。     

Electrical and chemical diagnostics of transformers insulation. B.Accelerated aged insulation samples

This paper describes the analysis of accelerated aged insulation samples to investigate the degradation processes observed in the insulation from aged power transformers. Short-term accelerated ageing experiments were performed on paper-wrapped insulated conductors and on pressboard samples. The condition of aged insulation samples was investigated by two relatively new diagnostic techniques: (a) measurements of interfacial polarization spectra by a DC method; and (b) measurements of molecular weight and its distribution by gel permeation chromatography (GPC). Several other electrical properties of the paper/pressboard samples were also studied. Possible correlations have been investigated among the different measured properties. The GPC results have been used to predict how power transformer insulation molecular weights change with temperature and time     

直流下局部放电序列信号检测与特性分析

介绍了用于分析直流下局部放电序列信号的时间等待恢复模型及其假设,总结了基于基本参数放电幅值q和放电时间点t用于分析直流局部放电序列信号的多种放电谱图。利用自行研制的直流局部放电宽带检测系统获取了缺陷模型(空气中电晕、油纸绝缘的尖板、内部缺陷和沿面放电)在直流电压下的大量局部放电脉冲波形-时间序列。并对获取的脉冲波形-时间序列,使用脉冲群快速分类技术进行随机干扰脉冲剔除。在上述工作基础之上,进行了直流局部放电幅值-时间序列信号的相关性统计分析,给出了各缺陷模型对应的典型q-t、n-q、n-Δt和qsuc-q等多种直流局放谱图。试验结果分析表明,四种典型缺陷具有各自的放电特性,直流下局部放电发展过程符合时间等待恢复模型及其假设。这为基于幅值-时间序列的直流局放检测、识别提供了理论和试验依据。