20号钢管材在高温时效过程中组织演变研究

针对石化装置中压力容器管线、蒸汽管道常用的20号钢,采用加速时效方法模拟了其组织状态的变化。研究结果表明,20号钢在加速时效过程中以珠光体球化、碳化物晶界析出为主要显微组织演变特征。初步建立了20号钢在加速时效过程中碳化物和晶粒长大的动力学方程。     

Aging of distribution cables in service and its simulation in the laboratory

This study focuses on efforts to characterize aging occurring in 15 kV distribution cables in a dry climate. It has been shown that similar changes can be produced by a suitably planned accelerated thermal aging testing in the laboratory. The Arrhenius equation is used for establishing the accelerated aging test parameters. Different modes of statistical analysis namely analysis of variance (ANOVA), Andersen-Darling test for normality, F-test, t-test are performed to validate results from accelerated aging tests with field aging     

Field and laboratory aging of polymeric cable terminations. II.Laboratory aging

For pt.I see ibid., vol.13, no.2, p.316-22 (1998). This paper presents the results of laboratory aging tests on polymeric cable terminations. The goals of the laboratory aging were two-fold: (1) develop an accelerated aging test that can simulate the changes produced in the field, and (2) provide an assessment on the magnitude of aging induced changes on the electrical performance of terminations. Monitoring leakage current and material changes during laboratory tests were useful for assessing the variations possible in aging due to experimental parameters used. It has been shown that a laboratory aging test that is based on evaluating the termination's leakage current suppression capability and the ability to withstand a moderate level of discharge activity is suitable not only for assessing the long term performance, but also for ranking the electrical performance in accordance with field exposure     

A new accelerated aging procedure for cable life tests

A new accelerated aging procedure for cable life tests has been proposed in this paper. The objective has been to minimize the total test costs using cable samples subject to the constraint that all relavant cable characteristics should be preserved by the samples. The procedure utilizes a combined approach based on available physical and mathematical models and laboratory accelerated aging tests. The behavior of dielectric strength, dielectric loss angle, capacitance and loss of mass in XLPE cable models subjected to different aging conditions (voltages and temperatures) has been monitored in order to verify the proposed procedure. Investigations have proven that the results concerning aging effects obtained under combined stresses (simultaneously electrical and thermal) are different from those obtained under single-stress aging. The degradations caused by combined stresses cannot be directly related to the changes caused by the single stress, i.e. their superposition is not valid. It has been found that tan delta can serve as a representative indicator of other cable properties relevant to aging phenomena.     

IGBT功率模块加速老化方法综述

功率变流器的可靠性评估和寿命预测已经成为非常重要的研究课题。IGBT功率模块的大量使用在诸多领域里越来越广泛,它们的失效主要由热机械疲劳引起,而在正常工作运行时,这种疲劳老化过程很漫长。因此,为全面观察和探究功率模块的疲劳老化失效过程,需要设计加速老化试验以缩短研究周期。最普遍的老化试验方法是对器件施加热应力和电应力,对器件不断热冲击实现加速老化进程的目的。文中主要归纳分析了各种加速老化方法的目的和差别,并重点总结了功率循环加速老化方法在不同试验条件、失效方式、试验持续时间、试验电路设计、监测的电气参数和热参数等方面的不同,目的在于提出加速老化方法的一般步骤和需要考虑的问题。最后根据这些问题对加速老化方法的研究进行了展望,为IGBT功率模块乃至整个变流器系统的失效机理分析、可靠性分析、寿命预测、健康状态评估和状态监测的研究奠定了基础。     

周期瞬态工况下IGBT交流加速老化方法研究

针对以往直流加速老化方法不能复现周期瞬态工况下IGBT工作特性的情况,提出一种对处于周期瞬态工况下H桥级联的IGBT模块进行交流加速老化的方法。首先对周期瞬态工况下的H桥级联拓扑进行分析,然后对PWM控制下的单相全桥IGBT损耗进行建模及分析,并且将直流加速老化和交流加速老化过程中功率模块的结温波动进行了对比分析,依据IGBT常用的寿命解析模型Lesit模型以及仿真结果说明等效全桥电路的合理性。最后设计并搭建了交流加速老化实验平台并与原始H桥级联电路仿真结果进行了对比分析。说明该交流加速老化方法可以为研究特殊工况下的IGBT可靠性提供一种新思路。     

Influence of accelerated aging on mechanical and structural properties of cross-linked polyethylene (XLPE) insulation

Contents  This paper describes results of laboratory accelerated aging test and the influence of different aging conditions on non-electrical properties of cross-linked polyethylene insulation (XLPE). Accelerated aging has been carried out on a cable model with different electrical and thermal stresses, and with thermal stresses in air or water as surrounding environment. Tensile strength, elongation at break, degree of cross linking and crystallinity degree of XLPE insulation have been measured and monitored. Received: 10 April 2000     

Behavior of post insulators during UHV dc test

This paper presents experimental results on post insulators subjected to ultra high dc voltages in the range of 1 to 4.8 MV. The behavior of new and aged insulators has been studied recently during diagnostic and accelerated aging tests, in order to characterize both their withstand and recovery voltages, as well as estimate their remaining life time. Estimation of their remaining life time enables a better prediction of maintenance intervals, thus avoiding unnecessary and costly downtime periods. Measurements of the recovery voltage also have been performed on insulators presenting defects, following dielectric failure in service. The results of the accelerated aging tests carried out demonstrates a faster assessment of the post insulators performance     

Allowance for insulation ageing in the new concept of acceleratedlife tests of high-voltage power transformers

It is pointed out that the existing system of type and acceptance tests of high-voltage transformer insulation does not take into account insulation aging, which is particularly objectionable with respect to equipment with reduced insulation levels. The authors propose a novel concept of accelerated life tests based on integrated simulation of basic operating loads both periodic (surge) and long-term ones, by performing a long-term accelerated test simulating the working conditions, with exposure of the test object and/or its insulation to periodic operating surges (overvoltages and overcurrents). This test replaces a group of conventional individual acceptance tests and provides more ample and more precise information on the performance and dependability of the equipment. The test procedure was checked in a test of a small lot of 1600 kVA 35 kV power transformers     

Quantification of degradation in nonceramic housing materials by laser ablation

A laser irradiation technique has been explored to quantify visible as well as invisible degradation of housing materials used for nonceramic insulators. Nonceramic insulators that were removed from service and new samples of the housing that were subjected to accelerated testing in the laboratory have been evaluated. The method uses a constant power laser source for delivering the same energy to the test specimen. The proposed method is fairly quick and could be looked upon as an additional method for characterizing aging of nonceramic insulators. It has been shown that this method provides a better characterization of aging than is obtained from Fourier Transform Infrared Spectroscopy. The housing materials evaluated include silicone rubber, ethylene propylene diene monomer rubber and cycloaliphatic epoxy resin.     

Field and laboratory aging of polymeric distribution cableterminations. I. Field aging

This, two-part paper, describes the results of a research project aimed at understanding the magnitude of aging of polymeric cable terminations used in distribution. The termination types evaluated are currently used; hence, they have satisfied IEEE Standard 48. This standard does not address the issue of aging. Terminations made from 3 different polymer families and porcelain were evaluated. Presented in Part I, are the results of field aging from 5 outdoor sites in the USA over a 3 year period; and in Part II, results from accelerated aging fog chamber laboratory tests. The results from field aging show that only minor changes were produced. Some differences were observed in the electrical performance of formulations within the same polymer family, and among different polymer families. However, it was concluded that the performance of the terminations evaluated would not be compromised by aging produced changes in the weathershed housing     

Multistress accelerated aging of polymer housed surge arresters under simulated coastal Florida conditions

Long-term performance of polymer housed surge arresters under multistress accelerated conditions simulating coastal Florida service environment in the lab has been presented. Commercial 9 kV ethylene propylene silicone blend (EPSB) and silicone rubber (SiR) arresters were procured and used for this purpose. Multi-stress aging was used to realistically and meaningfully simulate the actual service environment that has the synergy of several environmental stresses. The various stresses applied include ultraviolet-A radiation (UVA), rain, heat, clear mist, and salt fog. Summer and winter weather cycles were designed to apply these stresses cyclically as they occur in the service environment. This method provides a comprehensive evaluation of the insulator, the hardware and its attachment. Coastal Florida conditions were chosen as the year-around warm temperatures and the high humidity challenge any insulating material, ceramic or polymeric. The evaluation was conducted for a period of 15 simulated service years of aging (15 lab-years) in the multistress accelerated aging chamber. Compared to the unaged (virgin) sample, the EPSB arresters showed chalking, reduced hydrophobicity, and reduction in hydrocarbon (CH) group molecules in the attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) measurements. The SiR arrester surfaces showed no noticeable changes in the FTIR measurements. However, scanning electron microscopy (SEM) micrographs indicated increased surface roughness and disintegration of the material for both the SiR and EPSB surfaces. Research results indicated that multistress accelerated tests are desirable since they reflect the real world.     

基于指纹参量的环氧云母绝缘多因子老化的实验研究

局部放电的统计参量,即指纹参量是评定绝缘放电状态的重要参量,本文在实验室中进行了环氧云母绝缘电机线棒的多因子老化实验,在不同老化阶段测量了线棒的局部放电,并分析了放电参量各种分布的指纹参量,实验结果表明,相位分布的互相关系数及不对称度等指纹参量随老化时间呈现明显的变化规律,并且这些指纹参量与剩余击穿电压有较大相关性,所以,可以用局部放电指纹参量来评定环氧云母绝缘的老化状态。     

On the estimation of elapsed life of oil-immersed power transformers

Inadvertent failure of power transformers has serious consequences on the system reliability, economics, and the revenue accrual. An accurate estimation of transformer life can, to a very large extent, mitigate the problems, besides satisfying the conflicting requirements of optimum utilization of the equipment and safeguarding the reliability. In this endeavour, the authors have planned long duration aging experiments on scaled-down (prorated) models of a transformer, incorporating all of the essential features of actual equipment under normal operating electric stress and accelerated thermal stress. In continuation of the authors' earlier experimental investigations, an elapsed life assessment study has been instituted by acquiring insulation-aging data under accelerated thermal stresses.     

硅橡胶合成绝缘子耐老化性能试验研究

对合成绝缘子在污湿条件下电老化性能及实验室条件下人工加速老化性能进行了试验研究,针对硅橡胶合成绝缘子的全盘材料的电气老化性能、憎水性和力学性能等方面进行耐老化性能试验,并对在户外运行多年的合成绝缘子进行了综合性能测试.结果表明,合成绝缘子的耐老化性能好,能满足户外长期运行的要求.     

NaCl溶液对XLPE电力电缆工频击穿特性和水树的影响

采用同一根抗水树XLPE电力电缆,分别在自来水和NaCl溶液中进行60 d、120 d和180 d的加速老化试验,然后对老化前和老化后的电缆试样,分别进行工频逐级击穿,对老化后击穿的电缆试样进行水树检查。试验结果表明,NaCl溶液对抗水XLPE电力电缆的老化有明显的作用。     

交联聚乙烯电缆空间电荷与理化性能的关系

针对高压交联XLPE电缆,通过对未老化、加速老化1年和实际运行30年的电缆绝缘的空间电荷特性、力学性能及理化性能进行研究,分析了老化过程中电缆绝缘空间电荷分布与理化性能之间的关系。结果表明:沿电缆径向由内向外,未老化电缆电荷积累量增加,加速老化1年的电缆电荷积累量呈下降趋势,实际运行30年的电缆电荷积累量上升。结合力学性能及理化分析认为,加速老化电缆绝缘老化起始于绝缘内侧,并且影响到绝缘中间部位;而实际运行30年的电缆绝缘老化起始于绝缘外侧。     

紫外辐射对高温硫化硅橡胶性能影响初探

高温硫化(HTV)硅橡胶凭其强憎水性、憎水迁移性和恢复性等优越性能,成为合成绝缘子外绝缘的首选材料。然而,与无机材料相比,高温硫化硅橡胶更易受环境影响而老化,因此通过氙灯辐照对高温硫化硅橡胶进行紫外加速老化试验。采用静态接触角法测量和评价硅橡胶材料的憎水性,同时进行了硬度以及扫描电子显微镜(SEM)测试,另外采用image-pro plus 6.0软件对SEM图片进行测试分析。试验结果表明:短时氙灯辐照对高温硫化硅橡胶表面憎水性影响不大,材料硬度有变大趋势,材料表面凹凸不平,粗糙度变大,并有填充物外露的趋势。随着辐照时间增加,欲析出颗粒数目逐渐增多,颗粒大小逐渐变大,总面积增加。     

用超宽频带局部放电检测技术评定电机线棒老化状态的实验研究

在大型电机运行过程中 ,由于电、热、机械和环境应力的联合作用 ,其绝缘性能会逐渐下降。在实验室中通过多因子加速老化实验模拟了电机线棒在实际运行中的老化。对不同老化程度的线棒 ,使用超宽频带局部放电检测技术测试了试样的局部放电 ,并分析了放电信号在时域和频域随老化时间的变化情况。实验结果表明 ,随着试样线棒绝缘的不断劣化 ,放电脉冲时域波形的高频振荡不断加剧 ,脉冲宽度不断减小 ;同时 ,频域中的高频分量越来越丰富 ,谱峰逐渐增多 ,并且在高频段出现特征峰分布     

Inference of PD in electrical insulation by charge-heightprobability distribution. Diagnosis of insulation systemdegradation

This paper deals with application of stochastic procedures for the analysis of PDHD (partial discharge height distributions) detected during life of insulation systems. Experiments of accelerated aging under electrical stress were carried out on both an artificial flat cavity and a 23 kV epoxy-resin insulator, where PD are already active at the beginning of aging. A correlation between aging time and PDHD features is observed during long-term voltage application, until breakdown, on both objects. In particular, the PDHD analysis is approached by means of the Weibull function. It is shown that the time evolution of shape and scale parameters can provide diagnostic indications on aging amount, incoming failure and thus on the reliability of insulation systems