New diagnosis approach to epoxy resin transformer partial discharge using acoustic technology

This paper first investigates the correlation between acoustic signals and electric power-source signal angles using ultrasonic detection technique. This paper then compares said acoustic signals' three-dimensional patterns with their polar-coordinate patterns and, with angle-zones established, provides a new analyzing and identification method for partial discharge (PD) fault types. This method is applicable to field inspection and measurement and can help identify epoxy-resin transformers' PD fault types. We first produce specific PD fault types in the laboratory and receive PD signals using ultrasonic technique. Then, we adopt polar-coordinate patterns to analyze their characteristics, deduce said characteristics into zone-identification patterns, and apply the D parameters to identify fault types. After utilizing this analyzing method to field epoxy-resin transformers, we learn that its diagnosis ability is fine and effective.     

Tree growth monitoring by means of digital partial discharge measurements

In this work results relevant to electrical treeing tests performed on several ethylvinylacetate EVA (with different vinylacetate percentage) and on cross linked polyethylene (XLPE) (of two different lots) polymer materials are presented. During the tree growth the partial discharges (PDs) were monitored by means of a digital PD acquisition system and the tree morphologies were optically evidenced by means of video recorder equipment. The PD acquired data, the outcome of the video monitoring and the time-to-breakdown were off-line processed and analysed. In this way, two main results were obtained: the first one, applicable to this kind of laboratory treeing tests, is related to the possibility of predicting the lifetime of the specimens, considering a specific PD measurement derived quantity; the second one demonstrates the possibility to detect the tree morphology considering the phase-number distribution obtained by the digital PD measurement. The presented test procedures are deemed to have a potential for diagnostic applications.     

基于局部放电量的环氧树脂脉冲电应力老化特性研究

针对GIS内出现的冲击型电应力老化现象,设计一套特斯拉脉冲电源发生器,通过控制调节脉冲电压的输出幅值及频率,研究纳米Al2O3填料与环氧树脂共混填充在不同电压幅值、频率试验条件下的绝缘特性和局部放电量的变化规律.结果 表明,较高的脉冲幅值与脉冲频率会加快空间电荷的入射与脱陷过程,加剧复合材料内部局部放电过程,促进导电通道分支的发展,进而使复合材料的老化程度更加严重.该研究结果有利于提升电气设备缺陷发现能力,减小故障几率,缩短停电检修时间,为设备异常故障分析提供参考依据.     

Improvement of partial discharge (PD) resistance of epoxy resin by using sulfur-containing additives

In the field of high-voltage engineering, it has been desired for a long time to improve the internal PD resistance of epoxy resin without lowering other properties. Recently, the authors discovered that some sulfur compound as curing agents or simple additives improved the PD resistance of rubber markedly, and here an attempt has been made to apply this fact to the case of epoxy resin. As was expected, some sulfur compounds containing SS-bond suppress the deterioration of epoxy resin due to internal partial discharges, and the larger the molecular weight of organic group combining the SS-bond, the longer the effective life of additives. Moreover, to make full use of these additives, it is very important to restrict moisture in the insulation systems. From this study, the authors have proposed the chemical formulation of the suppressive effect of additives for deterioration of epoxy resin due to internal partial discharges.     

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.     

油浸式电流互感器内部局部放电故障的诊断分析

介绍了一起油浸式电流互感器由于内部绝缘故障导致运行中油色谱分析不合格,通过油色谱跟踪分析、红外热像检测、高压介损、局部放电测量等有效技术手段,准确推断出故障的真实原因,并经解体检查发现了互感器内部存在局部放电故障。     

A new test method for internal partial discharge resistance of insulating materials

A new test method for internal PD resistance of insulating materials has been studied intensively by a task force at CIGRE for over ten years. Recently, Method II, which was developed by the authors, is now being studied as the international round robin test proposed by a domestic task force. This paper describes the new test method concretely and shows some typical test results. The test electrode system is characterized by adhesion of test specimen to the embedded sphere electrode, and it may be applicable to all sorts of insulating material for the internal PD resistance test under uniform partial discharges. The most important point of this method is to realize the complete adhesion by skillful techniques. It was ascertained that the spread of test data may depend only on the uniformity of materials by this method, and excellent life data can be obtained for some specific materials.     

XPLE电树枝生长过程中局部放电SHF信号特性研究

交联聚乙烯(XLPE)电缆中电树枝的生长伴随局部放电(PD)的产生,二者间存在一定关联。XLPE材料绝缘强度较高,其中发生的PD在超高频(SHF,3～30 GHz)频段的信号幅值相对较高。文中采用基于针-板电极结构和XLPE绝缘材料的试样,在不同温度和电压下对电树枝生长过程中的形态和PD的SHF信号进行同步检测,分析了电压与温度条件对二者的影响,并研究了二者间的特征关系。研究表明XLPE中电树枝的长与宽和温度与电压呈正相关,电压较低时对分形维数较低,较高时分形维数无明显变化。SHF信号幅值也与温度和电压呈正相关关系,电压较高时,信号幅值呈现先增大再减小至平缓趋势,频率在电压较低时信号有一定程度下降。电树枝生长情况和SHF信号的幅值呈正相关关系,且当电树枝生长速度较快时,SHF信号的频率也会升高。     

Measurement of space charge distribution in epoxy resin

Internal space charge behavior of insulating materials has recently attracted attention of many researchers, and a large number of experimental studies were carried out by using the materials for dc cables, such as XLPE, LDPE, and HDPE. Epoxy resins are used for insulation under strong electric fields in power apparatus and in electronic devices, and we investigated the behavior of internal space charge using the pulsed electroacoustic method. Two types of epoxy resins were studied: insulation-grade and craft-grade. When dc electric fields were applied to the craft resins treated by immersing them into room-temperature water for 8 and 24 h, positive and negative charges accumulated near the anode and the cathode, respectively, and the charge distribution changed with the immersion time. On the other hand, no charge was observed in the insulation-grade epoxy resin. Next, we treated the samples by immersing them into 100 °C water for 8 h. When the sample was treated for 8 h, hetero charge distribution, which means positive charges near the cathode and negative charges near the anode, was observed. This result is consistent with a previous paper reporting that by chemical analysis, secondary decomposition had occurred. These results show that water and temperature influence the internal space charge behavior of epoxy resins. © 1999 Scripta Technica, Electr Eng Jpn, 129(3): 9–16, 1999     

环氧树脂灌封材料工艺性探讨

利用E-39D双酚A环氧树脂与酸酐固化剂METHPA、α—Al2O3填料及其他添加助剂，经机械共混固化后可得到具有优异电气性能和耐侯性能的灌封体系。探讨了影响环氧树脂灌封材料工艺性的各种因素；通过填料表面偶联处理实现了填料粒子在环氧基体中的良好分散，得出了具有良好工艺性的环氧灌封材料的工艺条件。     

现场局部放电试验中干扰源的识别和采取的对策

局部放电试验是检测固体绝缘中存在气泡和裂纹等缺陷最有效的手段,局部放电又是个弱电现象,现场进行局部放电试验极易受各种干扰的影响。文章详细分析了常见的干扰源类型和形成途径以及各种干扰波形放电特征、显示位置和随施加电压变化规律,并对各种干扰采取有效对策,将干扰抑制在合理的数值范围内,以保证局部放电试验顺利进行。     

对局部放电试验中典型放电和干扰图谱的分析

对现场测试中几种典型放电现象进行对比,并采取等效电路结合放电过程曲线,分析各种放电现象形成的原因及其明显特征,以便在错综复杂的图谱显示中找到规律,为正确识别放电信号提供参考。