直流下局部放电重复率的数学物理模型

本文基于绝缘内部气隙放电时的三电容等值和双电容简化等值两个电路分别研究了直流下局部放电重复率的数学物理模型,以及测量电阻存在时对直流局放重复率的影响。对交流下经典三电容局放模型加入电阻后的等值电路分析直流下简化局放过程得出:在局放存在条件下,直流下局放重复率与外部施加直流电压可近似为线性关系。对双电容简化等值电路的数学物理模型分析同样得出:出现局放时的直流下局放重复率与外部施加直流电压具有近似线性关系;测量电阻对直流下局放重复率的影响只是暂时的,会在局放起始放电条件不稳定的情况下对重复率有一定的影响,在到达平稳状态后,直流局放重复率仅由绝缘缺陷电气结构决定。基于宽带检测的直流平稳状态下三种基本油纸绝缘缺陷模型的试验结果则表明:在试验电压大于局放起始电压后,直流下局放重复率与一定范围内的试验电压值具有该近似线性关系。     

PD characteristics and mechanisms in artificial air-filled voids atroom and liquid nitrogen temperatures

In this study, partial discharge (PD) characteristics in artificial air-filled voids at room and liquid nitrogen temperatures were investigated experimentally. It was found that minimum PD inception voltage at liquid nitrogen temperature (77 K) decreased with decrease in ambient temperature due to condensation of oxygen in the void. By observation of PD current pulses and light images, it was found that there were three modes of discharge: streamer, Townsend and glow like discharges in PD at room and liquid nitrogen temperatures. Especially the mode at liquid nitrogen temperature changes markedly with the stress time     

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.     

Partial discharge inception characteristics under butt gap condition in liquid nitrogen/ PPLP/sup /spl reg// composite insulation system for high temperature superconducting cable

The partial discharge (PD) inception characteristics are studied in liquid nitrogen (LN/sub 2/)/polypropylene laminated paper (PPLP/sup /spl reg//) composite insulation system for high temperature superconducting (HTS) cable. Experimental results revealed that the magnitude of the initial PD increased as the PD inception electric field strength was increased, because the injected energy increased. Initial PD was generated at the first and third quadrant of applied AC voltage phase. The probability of initial PD at the positive and negative voltage phase was almost the same. The reason is because liquid nitrogen is a nonpolar molecule and we used symmetric electrode configuration with uniform electric field distribution. Finally, it was pointed out that PD inception electric field strength (PDIE) depended on the volume of the butt gap because of the increasing probability of weak points of electrical insulation, and PDIE linearly decreased with increasing stressed volume of the butt gap in the log-log scale.     

特高压换流站直流滤波电容器故障分析研究

针对常发的直流滤波器用直流电容器损坏事故,本文对特高压换流站直流滤波电容器事故的机理和原因进行深入的研究,对电容器单元进行了外观和电性能测试、绝缘油色谱试验、电容量介质损耗测量.对解剖后的电容器元件绝缘包封、电容器元件不同温度下直流电压击穿、聚丙烯薄膜不同温度下交直流电压击穿、铝箔等进行了研究试验.通过对故障和完好电容器对比试验研究,发现所测电容器的部分生产工艺和注油工艺不佳造成运行中电容器不稳定,而电阻过于集中,导致电阻器表面绝缘介质过热,容易发生击穿故障,研究结果对提高该类型电容器的运行可靠性具有重要意义.     

Selectivity of damped AC (DAC) and VLF voltages in after-laying tests of extruded MV cable systems

The purpose of HV after-laying tests on cable systems on-site is to check the quality of installation. The test on extruded MV cable systems is usually a voltage test. However, in order to enhance the quality of after installation many researchers have proposed performance of diagnosis tests such as detection, location and identification of partial discharges (PD) and tan /spl delta/ measurements. Damped AC voltage (DAC) also called oscillating voltage waves (OVW) is used for PD measurement in after-laying tests of new cables and in diagnostic test of old cables. Continuous AC voltage of very low frequency (VLF) is used for withstand voltage tests as well as for diagnostic tests with PD and tan /spl delta/ measurements. Review on the DAC and VLF tests to detect defects during on-site after-laying tests of extruded MV cable systems is presented. Selectivity of DAC and VLF voltages in after-laying testing depends on different test parameters. PD process depends on type and frequency of the test voltage and hence, the breakdown voltage is different. The withstand voltage of XLPE cable insulation decreases linearly with increasing frequency in log scale. Experimental studies with artificial XLPE cable model indicate that detection of defects with DAC or VLF voltage can be done at a lower voltage than with DC. DAC voltage is sensitive in detecting defects that cause a breakdown due to void discharge, while VLF is sensitive in detecting defects that cause breakdown directly led by inception of electrical trees.     

PD characteristics in an air-filled void at room temperature undersuperimposed sinusoidal voltages

Partial discharge in an artificial air-filled void under superimposed sinusoidal voltages is investigated at room temperature in order to clarify the effect of voltage superposition. The applied voltage waveform is composed of a 60 Hz fundamental sinusoidal wave and a high frequency sinusoidal wave of 300 Hz to 1.2 kHz. It was found that PD started when the peak value of the superimposed voltage reached the PD inception voltage under 60 Hz sinusoidal voltage. Also, PD occurrence frequency increased remarkably when the peak value of the high frequency component exceeded a critical value, which is smaller than the PD inception voltage under 60 Hz sinusoidal voltage. PD characteristics under such conditions were discussed as the effect of the residual voltage, caused by the surface charge deposited in the void by the preceding PD. The obtained experimental results suggest that the superposition of high frequency component accelerates the degradation of the solid insulator containing void defects     

某变电站500kV均压电容器介质损耗超标分析

对某变电站500kV断路器均压电容器的介质损耗试验,发现部分运行中的油纸式断路器电容器在10kV下介损值不合格。而在额定电压下的高电压介损值却合格的现象。     

V-t characteristics of partial discharge inception in liquid nitrogen/ PPLP/sup /spl reg// composite insulation system for HTS cable

In this paper, we studied partial discharge (PD) inception characteristics and V-t characteristics of PD inception in liquid nitrogen (LN/sub 2/)/polypropylene laminated paper (PPLP/sup /spl reg//) composite insulation system for high temperature superconducting (HTS) cable. Experimental results revealed that the magnitude of initial PD was in the range of 2.0-30 pC irrespective of butt gap condition and the initial PD was generated at the first and third quadrant of voltage phase. PD inception electric field strength (PDIE) without butt gap was 5-10% higher than that with butt gap and thicker butt gap gave larger PDIE drop. Moreover, PDIE with butt gap depended on the butt gap thickness and the number of PPLP/sup /spl reg// layers. The reason is explained by the existing probability of weak points of electrical insulation at butt gap. Finally, lifetime indices n of V-t characteristics at PD inception were obtained as 80-100 irrespective of butt gap condition. These values showed enough flat characteristics of V-t phenomena of electrical insulation.     

选好高压并联电容器的额定电压和绝缘水平

对如何根据电网的实际运行电压、系统的短路容量、电容器组的容量、串联电抗率等因素,选用合适的高压并联电容器的额定电压;对如何根据电容器组在电网中的结线方式、电容器外壳接地与否等因素,选择电容器的绝缘水平,进行了说明.并指出正确选择额定电压和绝缘水平对高压并联电容器在电网中安全、无故障运行的重要性.     

Accelerated cable life testing of EPR-insulated medium voltagedistribution cables

This paper presents results aimed at developing a reliable accelerated aging tank test for EPR-insulated cables. Aging was performed at 2 to 4 times rated voltage on load cycling to temperatures of 45°C, 60°C, 75°C, and 90°C at the conductor with water in the conductor strands and outside the cable. Results show that cable failure is more rapid at the highest electrical stress and lowest conductor load cycle temperature. Cables aged at higher temperatures and various levels of electrical stress rarely failed and retained in excess of 40% of their original breakdown strength after 1500+ days of aging. Aging performed at 90°C load cycle temperature and 4 times rated voltage with air on the outside and water at the conductor of the cable showed more rapid loss of life than with water outside. Results indicate the optimum aging conditions for EPR-insulated cables in the accelerated cable life test (ACLT) differ significantly from those previously observed for XLPE-insulated cables, and that the appropriate test methodology for EPR-insulated cables requires additional study     

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。     

Partial discharge behavior in switching-surge-aged oil-papercapacitor bushing insulation

Partial discharge (PD) diagnostics are utilised to examine the aging process of mineral oil-impregnated-high density kraft paper capacitor bushing models, subjected to repetitive voltage switching surges. It is demonstrated that the PD measurements of cumulative apparent charge transfer and discharge inception stress constitute an effective means for assessing aging and its reversibility due to gas evolution and re-absorption or solubility of a mineral oil-impregnated-paper insulation system in the presence and absence of switching surges. While the experimental results indicate that electrically overstressed solid-liquid insulation can recover in part its initial electrical properties following an electrical stress-free period, long term stability is only effectively achieved by a reduction in the switching surge overstress through an increase in the overall insulation thickness. The electrical stress levels, employed in the experiments, are found to be not sufficiently elevated to lead to any detectable partial discharge formation within the oil phase itself; the observed discharge behavior is rather characteristic of the type that is normally associated with macroscopic cavities occluded within the oil-paper insulation systems     

选好高压并联电容器的额定电压和绝缘水平

对如何根据电网的实际运行电压、系统的短路容量、电容器组的容量、串联电抗率等因素,选用合适的高压并联电容器的额定电压;对如何根据电容器组在电网中的结线方式、电容器外壳接地与否等因素,选择电容器的绝缘水平,进行了说明。并指出正确选择额定电压和绝缘水平对高压并联电容器在电网中安全、无故障运行的重要性。     

对断路器电容器电容及介损测量预试方法的探讨

在预防性试验中,经常发现断路器端口并联的均压电容器介损超标问题,如果全部更换就会带来较大的经济损失。究其原因是选择的试验电压不当造成的,提高试验电压后,大部分电容器介质损耗趋于正常水平。所以,试验电压越接近额定电压结果越能表现其绝缘性能的真实性。     

对断路器电容器电容及介损测量预试方法的探讨

在预防性试验中,经常发现断路器端口并联的均压电容器介损超标问题,如果全部更换就会带来较大的经济损失。究其原因是选择的试验电压不当造成的,提高试验电压后,大部分电容器介质损耗趋于正常水平。所以,试验电压越接近额定电压结果越能表现其绝缘性能的真实性。     

高压并联电容器额定电压的选择探讨

介绍了目前在工程上常用的关于高压并联电容器额定电压的选择方法;指出在电网谐波含量较大的情况下存在着谐波危害电容器安全运行的问题;提出了可以参照滤波电容器额定电压选择方法来选择并联电容器的额定电压,把谐波电压考虑到电容器的额定电压之中的建议,确保电容器在谐波条件下的安全可靠运行。     

Examination and location of partial discharge sites in severelyaged underground distribution cables

This paper presents the results of laboratory investigations of partial discharge (PD) in field aged XLPE underground power cables. PD measurements were made on sixty-one cable samples over a three year period. When PD was detected, the magnitude was measured and a site location was determined. PD site locations were predicted using time delay estimations between PD pulses arriving at opposite ends of the test cable. Fourteen of the samples tested had detectable levels of PD. Some of these PD sites extinguished during the measurement period and were returned to rated voltage aging. When samples had continuously active PD sites, they were either dissected or returned to the aging test. Four sites of this type were found allowing two for dissection and two for aging. Seven of the samples failed after PD measurements. All seven failed near the predicted PD location. During the PD testing, no test cables contained PD which initiated at or below operating voltage. When PD detection equipment was monitoring cables which failed, the failures occurred from 2 to 80 minutes after the presence of PD pulses was detected     

有效散热面积对电力电容器外壳散热量的灵敏度分析

在介绍电容器传热过程数学模型的基础上,运用局部灵敏度分析方法,进行了有效散热面积对电容器外壳散热量的灵敏度分析,得到其灵敏度系数与电容器外壳温度、冷却空气温度之间的关系。实际算例分析表明,在额定电压及容量相同的情况下,相对于较小尺寸电容器,较大尺寸电容器的内部介质温度及外壳温度可降低2℃以内。     

温度对电缆附件界面缺陷处局放引发影响机制研究

温度对局部放电(partial discharge,PD)的发展过程有着重要的影响,但温度对PD的引发机制目前尚不明确。针对温度变化对电缆附件界面缺陷处PD引发机制进行研究。首先,对电缆附件界面单元与缺陷位置进行设计与仿真,并对界面单元不同温度下气隙缺陷PD特征进行测量。然后,搭建含有半导电层突起缺陷的电缆电热老化平台,通过电流通断模拟冷热负荷对电缆运行温度的影响。对界面单元和缺陷附件的局部放电起始电压（partial discharge inception voltage,PDIV）和PD相位谱图（phase resolved partial discharge,PRPD）进行对比分析,结果表明：随着测试温度的升高,界面单元的PDIV从8.3 kV降至6.9 kV,局部放电量有大幅提升,PRPD图显示出明显的内部放电特征。真实电缆附件缺陷处PD则会在温度快速上升时出现短暂的活跃,此时局部放电量与局部放电数都会出现明显增加,温度稳定后PD逐渐被抑制。上述现象主要与温度变化导致的界面处空间电荷分布和界面材料热胀冷缩所带来的“呼吸效应”有关,研究结果表明：真实电缆附件在大温度梯度下进行局放测试可提高局放检出率,为解决传统测试对局放检出可靠性不足提供了理论依据。