大型发电机定子绝缘的局部放电老化与提高运行可靠性

本文根据大型发电机高压定子线圈绝缘的运行经验及试验数据分析,提出10.5～13.8kV 发电机定子线圈沥青云母绝缘的电老化,主要是局部放电引起。为了提高运行可靠性,作者提出降低定子线圈绝缘的最大电场强度、中性点与引出端倒位运行,以及向主绝缘与导线之间的气隙灌注环氧树脂合成物。     

发电机定子线棒绝缘老化后不同部位参数比较

分别测量与研究了大型发电机主绝缘的槽部、出槽口和端部这 3个不同部位的真机线棒绝缘的tanδ、超声声速、动态力学参数和绝缘强度等 4种参数。试验研究发现出槽口附近的主绝缘老化最为严重 ,这对于大型发电机的维护和主绝缘老化状态的有效评估有重要意义     

汽轮发电机定子线圈端部磨损原因分析及处理

俄制TBB系列大型汽轮发电机在国内应用中,普遍存在定子线圈端部磨损情况,严重影响着发电机安全稳定运行。本文就俄制TBB-500-2EY3型汽轮发电机定子线圈端部磨损原因分析及处理过程进行总结探讨。     

27kV级发电机定子线圈绝缘研制

随着电力行业的飞速发展，国内迫切需要单机容量达百万级的发电机。到目前为止，27kV级的定子线圈的试制研究在国内尚属首次，27kV定子线圈主绝缘的研究对1000MW级的大型汽轮发电机的国内制造起着至关重要的作用。本文介绍了27kV定子线圈的研制过程，探讨了27kV定子线圈的绝缘结构，从介质损耗、主绝缘击穿强度、机械强度、玻璃化温度、快速电老化和防晕等方面，对27kV定子线圈主绝缘的性能进行了研究，并与国外同类线圈主绝缘进行了对比，得出自行研制的27kV级定子线圈的主绝缘基本达到国外同类产品的要求的结论。     

大型汽轮发电机定子绕组端部二倍频测量及模态分析

文章分析了大型汽轮发电机定子线棒端部受力情况 ,指出当发电机线棒产生二倍频振动时 ,定子绝缘所受到的各种危害。为了消除危害发电机安全运行的隐患 ,介绍了发电机端部线圈二倍频测量和整体模态试验方法     

大型空冷汽轮发电机定子线棒制造工艺研究

本文根据大型空冷汽轮发电机的结构特点,重点研究了端部成型、导线压制以及主绝缘模压等定子线圈的制造工艺,并就端部成型及模压等一些关键工序所采取的新工艺和新工具与水冷定子线圈进行了对比,进而形成了一套完整的空冷定子线圈制造体系。     

发电机定子线圈端部表面电位测量

发电机定子线圈部表面电位测量是一项新的试验项目，对线圈端部起到了监督作用，进一步提高了发电机安全运行的可靠性，本文介绍了在现场试验中的实际效果和经验。     

大型汽轮发电机组定子端部线圈引出线固有频率测试与分析

针对大型汽轮发电机定子端部线圈引出线由于受到电磁力的作用而振动 ,导致其绝缘磨损而引发的发电机短路事故 ,提出通过测量其引出线固有频率的方法是抑制发电机定子端部线圈引出线振动的必要检测手段。详细阐述了引出线固有频率测试的基本原理、测试仪器、测试方法 ,并用内蒙古达拉特发电厂 330MW发电机的端部线圈引出线进行实测分析。在测试分析中提出了引出线的振动幅值在评判中的重要作用 ,并认为采取引出线加配重降低其固有频率的方法要优于加强引出线强度提高其固有频率的方法。     

发电机定子绕组端部动态特性试验的实践意义和标准掌握

用事故实例分析了发电机定子绕组端部绝缘磨损故障的成因和后果，介绍了确定发电机运行时定子绕组端部振动特性的静态试验方法--发电机定子绕组端部动态特性试验的基本概念，并通过试验实例说明了该项试验在保障发电机安全运行避免重大事故方面的重要实用意义，随后介绍了我国相关的试验标准，指出了不同标准的异同之处和根据实际情况协调运用标准的基本原则。     

大型汽轮发电机定子端部绕组模态分析研究

分析了大型汽轮发电机定子湍部结构振动的机理。应用SPS395动态信号分析仪、STAR模态分析软件对发电机端部结构进行模态试验分析，并提出对发电机端部结构的处理意见，以使发电机端部结构的椭圆振型避开两倍的发电机基频，从而减少发电机端部结构的振动，提高发电机的安全运行。     

基于局部放电和超声波法研究大电机定子绝缘的老化特性

对谏壁电厂 7号机 (18kV ,30 0MW )更换线棒进行了多因子加速老化试验 ,在线棒的不同老化阶段进行了局部放电和超声波声速试验。试验发现 ,局部放电平均值是反映绝缘缺陷最好的参数 ,在局部放电统计参数中 ,放电平均值相位分布的偏斜度最能反映绝缘的老化程度。超声波声速试验的结果显示出 ,超声波声速可以表征发电机定子绝缘老化状态 ;随着线棒老化时间增长 ,其超声波声速明显降低。两项试验结果一致地表明 ,绝缘老化是由于其内部出现了微观缺陷     

用最大放电量增加率评定定子绝缘老化状态

进行了大电机定子线棒多因子老化实验 ,实验表明在电机定子线棒多因子老化过程中其最大放电量没有明显的变化规律 ,仅用最大放电量评定定子绝缘的老化状态有一定的局限性。提出了用最大放电量增加率来评定电机绝缘老化状态的新方法并验证了该方法的有效性     

Effect of manufacturer, winding age and insulation type on stator winding partial discharge levels

With thousands of machines monitored for as long as 25 years with the same method, on-line partial discharge (PD) testing has become a recognized, proven tool to help maintenance engineers identify which stator windings need off-line testing, inspections and/or repairs. With over 63,000 test results acquired with the same test method, what constitutes a winding with low, moderate or high PD has been identified. This paper presents tables that enable test users to easily identify with some certainty which stators are likely to suffer from groundwall insulation deterioration, with only a single measurement on a machine. The practical importance of these tables is that if one applies PD sensors to a machine and, in the first measurement, one obtains a Qm that exceeds the 90 percentile of the relevant Qm distribution, then one should be concerned enough at the PD level to take action, such as more frequent testing and/or off-line tests and inspections at the next convenient machine shutdown. Within the statistical accuracy possible with several thousands of independent results, it seems that critical PD levels only depend on operating voltage, hydrogen pressure, manufacturer, and the specific type of PD sensor and instrumentation used.     

An acoustic diagnostic technique for use with electric machineinsulation

Many of the electrical failures of large electric machines have mechanical precursors. This premise has led to the attempts described here to detect mechanical changes, such as groundwall delamination, by acoustic methods as a means of early detection of incipient failure. By optimally launching an ultrasonic wave into a stator bar and using the conductor as a waveguide, it has been shown possible to interrogate the groundwall insulation and the critical interface region adjacent to the conductor. Laboratory studies using an epoxy mica stator bar subjected to thermal cycling have demonstrated that the acoustic signatures obtained with this method are mirrored by conventional corona spectroscopy conducted simultaneously, although earlier damage is clearly discernible. Based on the results of this study, the acoustic technique appears to have substantial promise as an advanced detection tool     

Insulation systems and monitoring for stator windings of largerotating machines

The condition of the insulation system frequently limits the useful life of the windings of a rotating machine. This is a function of thermal, electrical, environmental, and mechanical factors plus the type of duty to which the machine is subjected. The thermal classifications of the variety of insulating materials that make up an applied insulation system are presented. Strand and turn insulation, common groundwall insulation systems, armor tapes and coatings, side packing and wedging methods, are discussed. Four factors that influence insulation life are identified: thermal, electrical, ambient (environmental), and mechanical plus performance (intended) and duty (mode of operation). Finally, accelerated aging tests, inspections and diagnostic test during service outages, and online monitoring of partial discharges are discussed     

透平发电机定子绕组端部动态特性和振动试验标准分析

本文介绍了《透平型发电机定子绕组端部动态特性和振动试验方法及评定》机械行业标准,对标准评定准则的制订进行了简略的阐述,并与JB／T8990—1999《大型汽轮发电机定子绕组端部模态试验分析和固有频率测量方法及评定》机械行业标准进行了对比分析,有助于对标准的认识和应用。     

Measures and technologies to enhance the insulation condition monitoring of large electrical machines

The utility of condition monitoring of the stator insulation structure of large machines has been enhanced substantially by the use of computer-based analysis of partial discharge signatures. A number of indices are examined through tests in a multistress aging facility to assess their promise in describing insulation degradation in machine insulation. In transitioning such tests to the field environment, an operational test is also described which offers some promise in identifying degradation without prior baseline data for a machine. On the basis that most electrical failures have mechanical precursors, acoustic methods are described for assessing stator bar mechanical integrity. This includes both using the conductors as waveguides and also employing acoustic emission for the location of large discharges.     

An online groundwall and phase-to-phase insulation quality assessment technique for AC-machine stator windings

An online technique for monitoring the condition of the groundwall (GW) and phase-to-phase (PP) insulation for three-phase ac-machine stator windings is proposed in this paper. Insulation-condition indicators such as capacitance, dissipation factor (tan/spl delta/), and ac insulation resistance are calculated online based on the differential leakage-current measurements for each phase. A model for a three-phase ac-machine insulation system is derived and analyzed for both offline and online testing. Guidelines for interpreting the measured indicators for determining the: 1) overall condition and 2) significant degradation in the individual GW and PP insulation for each phase of the stator are given based on the analysis. Experimental results on a 15-hp induction motor under intentional GW and PP insulation degradation conditions show that incipient insulation degradation can be detected and classified with high sensitivity.     

大型发电机组启动电气试验中的问题探讨

在发电机启动电气试验中, 要进行短路试验以检查发电机定子和转子绝缘情况。为了节省试验时间和试验费用, 可以用主变高压侧短路试验代替发电机机端短路试验。在发电机空载试验时不能做定子匝间绝缘试验, 防止损伤定子绝缘。同时, 在发电机启动过程中, 必须对机组的重要继电保护进行校验, 以确保正确发挥保护的功能。     

基于脉冲波形时域特征的局部放电识别

建立了一套数字化实时高速局部放电波形测量系统,由简单实验室模型和工业仿真模型取得了不同类型局部放电的脉冲电流波形,包括空气中和油中尖板电极放电,电机模型线棒内部气隙放电,线棒端部沿面放电,用分段的时域数据压缩法提取了脉冲波形特征,采用分级人工神经网络进行放电模式识别,以得较好效果。