基于超声脉冲反射法评估大电机定子绝缘的老化状态

该文提出一种基于超声反射法的大电机(300MW，18kV)主绝缘状态诊断方法。用这种方法可以测量超声纵波在主绝缘中传播的统计最小声速，统计平均声速，声衰减和统计缺陷率。在实验室分别对已运行16年、18年、23年和新的定于线棒进行了试验研究，并在发电机现场进行了定于绕组超声检测试验。试验结果表明，统计最小声速和统计平均声速随绝缘运行年数的增长不断减小，统计最小声速减小的趋势比统计平均声速更明显，严重老化的主绝缘由超声检测得到的统计缺陷率增大。大电机定于绕组的超声现场检测试验验证了超声反射法在发电机小修条件下的应用性。超声反射法是一种有效的、实用的大电机主绝缘状态诊断方法。     

Application of ultrasonic pulse-echo method to insulation condition diagnosis for large generators

It is a challenge to diagnose insulation condition of stator bars using an ultrasonic technique, due to the complex structures of the stator bars and the high attenuation of the stator insulation. In this paper, five low frequency transducers were used in a pulse-echo configuration to try to test a standby stator bar of a generator (300 MW, 18 kV). With an available transducer, four types of insulation structures were tested on the stator bar. The short side insulation was compared with the large one of the stator bar in the slot. The stator bar near the exit from the slot and the end stator bar, were compared with the stator bar in the slot. The semiconductive coating covered stator insulation was compared with the uncoated one. The stator insulation having an insulation-copper interface was compared with that having an insulation-gas interface. In addition, insulation diagnosis tests in the laboratory were performed on two sets of stator bars, which had been in service for 18 and 23 years, respectively in two generators (300 MW, 18 kV). Field tests were performed on the stator bars near the exit from the slot and the end stator bars of a generator (300 MW, 18 kV). The experimental results demonstrated an availability of low frequency ultrasonic pulse-echo method for insulation condition diagnosis of large generators     

大型空冷汽轮发电机模压定子线棒绝缘结构研究

研究了多胶模压的大型空冷汽轮发电机定子线棒绝缘体系,包括定子线棒的导线绝缘结构、主绝缘结构、防电晕结构、定子线棒制造工艺。通过性能指标测试确定了所用主绝缘材料、防晕材料,最终对定子线棒进行了性能评定。确定了大型空冷汽轮发电机定子线棒绝缘结构、膜压工艺。真机线棒结果表明:定子绝缘厚度薄、电性能高,绝缘的设计场强超过了3 kV/mm。     

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     

大电机环氧云母定子绝缘超声波速的研究

本文用A型脉冲回波法超声波检测系统，详细研究了大地机定子线棒不同的绝缘部位对检测超声波速的影响，以及波速随绝缘老化的变化规律。结果表明：大电机定子线棒的正面绝缘适合于超声检测；线棒表面半导体层的存在更有利于超声检测；超声波速能用来表征绝缘的老化状态。     

大型发电机定子线棒VPI用绝缘材料的国产化应用研究(Ⅲ)

为保证国产VPI(Vacuum Pressure Impregnating,真空压力浸渍)绝缘材料的性能稳定,对VPI绝缘材料进行了性能检测,并采用优选出的材料制造真机试验线棒。首先从两方面检测国产VPI绝缘材料性能,一方面对新批次少胶带的关键项目及以前没有检测的项目进行检测,国内外的浸渍漆新增加检测项目(机械性能、玻璃化转变温度、吸水率、电气性能)进行检测;另一方面利用ALSTOM试验方法检测VPI材料的耐热稳定性。然后选用各项性能均合格的国产VPI绝缘材料制作真机线棒,并对线棒的电性能进行检测。试验结果表明A厂和B厂自制的真机试验线棒具有优良的电气性能,除个别值外性能指标都达到了CEEIA/154-2003大型水轮发电机产品质量分等标准的优等品水平。     

大电机主绝缘剩余寿命智能评估的超声技术

研制了大电机主绝缘剩余寿命的超声智能评估系统。该系统采用超声脉冲回波检测方法和虚拟仪器技术开发平台,在已运行16、18、23年的300MW发电机定子线棒主绝缘和备用定子线棒主绝缘超声声速统计数据库的基础上,通过测量主绝缘的超声最小声速和平均声速,可智能预测最可靠和95%可靠剩余运行年数。一台已运行23年的300MW发电机的现场试验证明,评估结果对发电机的安全运行具有指导意义。     

汽轮发电机定子条式线圈低温真空干燥工艺的应用研究

分析了汽轮发电机定子线圈绝缘的密实性，整体性对线圈电气性能的影响，局部放电与绝缘中气隙的关系。阐述了定子线圈绝缘实性，整体性差的原因。论述了绝缘抽真空过程，确定了低温真空干燥工艺参数。给出了此种干燥法的结果及存在的问题。得出了如下结论：对汽轮发电机定子线圈进行低温真空干燥处理是可行的，但应采取适当的保护措施。     

660MW20kV汽轮发电机定子线圈VPI应用研究

从VPI工艺制造的样棒主绝缘性能试验出发,不断调整VPI工艺参数,得到适合660 MW定子线棒制造的VPI工艺.分析了采用真空压力浸渍绝缘工艺制造的660 MW定子线棒主绝缘的电气性能、力学性能.并与标准JB/T 56082中的多胶模压主绝缘性能进行了对比分析,结果表明,采用VPI浸渍工艺制造的定子线棒主绝缘完全达到并超过行业标准中优等品的要求.     

发电机定子线棒绝缘超声波速的研究

用超声纵波脉冲反射法,对不同运行年数发电机退役的定子线棒绝缘进行了超声检测试验,根据测到的 超声脉冲A扫描F波和B波的间隔时间编制了波速计算程序并计算了超声测量试验获得的A扫描波形。研究发 现,测到的定子绝缘最小波速和平均波速随着发电机运行年数的增长不断减小,且最小波速比平均波速减小的趋 势更明显,最小波速和平均波速能有效反映发电机定子绝缘的老化状态。     

超声波技术在大电机绝缘检测中的应用研究

用研制的检测系统 ,对大电机定子线棒进行了绝缘超声波参数测量和绝缘缺陷的检测试验。结果表明 ,使用 0 5MHz、 0 8MHz和 1 2MHz的超声换能器 ,此系统可以测量大电机定子绝缘的超声波参数 ,从而使超声波技术成为一种绝缘老化状态的诊断方法 ;0 8MHz的探头对定子线棒老化早期的绝缘缺陷能得到特征明显的超声A扫描波形 ,为对绝缘介电性能有直接破坏作用的绝缘断裂性裂纹的检测和识别提供了方法 ,对预防因绝缘裂纹导致绝缘击穿、发电机非计划停机具有重要意义。与国际上相同领域内超声波斜入射的透射波法比较 ,本文的超声回波法更具有应用前景     

大型发电机定子槽楔松动的动力学分析与检测

大型发电机的定子线棒在运行过程中受交变电磁力作用发生振动,这会引发定子线棒主绝缘磨损,最终导致绝缘性能下降.工程上通常采用槽楔波纹板结构对线棒进行固定,但由于线棒长期振动,槽楔出现松动不可避免,因此定期检测槽楔松动程度对电机安全运行具有重要意义.介绍了一种检测定子线棒松动程度的方法,即通过检测撞击到槽楔表面的冲击体的回弹速度来表征波纹板形变量大小.针对定子槽固定结构建立波动力学模型,重点分析了该检测方法的原理,并通过波纹板不同形变量下的动力学实验,验证了理论分析的正确性及该测量方法的可行性.最后对误差影响因素进行分析,计算该测量方法的准确率.     

基于模糊输出BP神经网络的电机主绝缘老化状态评估方法

评估大电机主绝缘的老化状态是电气工程领域中的重要课题，其目标是根据非破坏性参量评估绝缘的老化状态，然而传统的评估方法一直没有得到准确可靠的评估结果。为了克服传统的绝缘状态阈值评估方法的缺点，提出应用神经网络和模糊数学结合评估绝缘状态的新方法。由于绝缘的老化状态是一种模糊现象，所以建立了具有模糊输出的3层BP神经网络对绝缘状态进行评估，并确定了绝缘状态论域上的四个模糊子集及其隶属函数，同时规定了网络的输入和输出参量。选择Levenberg-Marquardt快速学习算法对该文建立的模糊输出神经网络进行了训练，并使用另外10组多因子加速老化数据和5组真机线棒数据对网络的评估能力进行了检验，检验结果表明该方法可以准确有效地评估定子绝缘的老化状态。     

大型水轮发电机定子线棒介质损耗测量探讨

绝缘介质损耗是反映高压电气设备绝缘性能的一项重要指标.介损的测量值直接影响对绝缘性能的判断.本文结合三峡工程左岸、右岸及地下电站的定子线棒出厂试验实际情况,就定子线棒介损测量的有关问题进行分析.探索适合水轮发电机定子线棒的介质损耗测量的方法.     

大型水轮发电机定子线棒绝缘厚度减薄研究

针对国内大型水轮发电机定子线棒绝缘与国外先进水平的差距,进行了长期的试验研究,完成了定子线棒绝缘厚度减薄的研制.减薄后的定子线棒绝缘达到了国外先进水平,满足了三峡发电机设计制造的要求.     

A remote and sensorless thermal protection scheme for small line-connected ac machines

An advanced remote and sensorless thermal protection technique for small line-connected AC machines is proposed in this paper. The proposed technique includes an algorithm for detecting abnormal cooling conditions due to reduced motor cooling ability, in addition to a stator resistance (R/sub s/)-based stator temperature (T/sub s/) monitoring scheme. The motor cooling ability monitoring algorithm can be implemented using the R/sub s/ estimates of an existing DC-injection-based R/sub s/ estimation scheme without parameter information or additional hardware. In addition, the influence of the fuse, circuit breaker, and cable resistances on the R/sub s/ estimate is investigated, and methods for compensation are suggested for improving the accuracy of the R/sub s/ estimate and, therefore, the reliability of T/sub s/ monitoring. Experimental results under a number of abnormal cooling conditions verify that the reduced cooling ability of the motor can be reliably detected and that it can be used in addition to the T/sub s/ estimate for complete motor thermal protection.     

Induction-motor stator and rotor winding temperature estimation using signal injection method

A new method to estimate the induction-motor stator and rotor resistance (R/sub s/ and R/sub r/) and temperature (T/sub s/ and T/sub r/) was proposed in this paper. Two signals with proper frequencies that yield high sensitivities of the terminal measurement to R/sub s/ and R/sub r/ at a given rotor speed are injected to the induction machine to estimate R/sub s/ and R/sub r/. The estimated R/sub s/ and R/sub r/ are then used to estimate T/sub s/ and T/sub r/, respectively, according to the relationships between R/sub s/ and T/sub s/, and R/sub r/ and T/sub r/. Simulation and experimental work have been carried out to verify the proposed method. The proposed method can estimate both stator and rotor resistance and temperature with high accuracy, and the estimated R/sub s/ and R/sub r/ can be updated in real time. It does not require an additional hardware or a large amount of finite-element analysis (FEA) or experimental data for implementation.     

高压电机定子线圈低温真空处理效果之探讨

本文对以环氧粉云母带为主绝缘的高压定子线圈,经低温真空处理的后果进行了探讨和分析。以往一股公认低温真空处管是有好处,作者认为不能一概而论。对液压或VpI绝缘有好处,但对热模压成型者,无利且有害。最后提出了新工艺方法,以弥补这种缺陷.     

Partial discharge, dissipation factor, and corona aspects for high voltage electric generator stator bars and windings

High voltage stator windings in modern electric generators are subject to high electrical, mechanical, and thermal stress. Operation of these machines in both air and high pressure hydrogen results in different considerations. Operation in the air environment does not offer the dielectric advantages of operating in high-pressure hydrogen. The two major design factors that are significant for the design of high voltage stator bars to be operated in air, are corona activity and PD activity. These of course are closely related. With the movement to increasing the power density of generators, which means operation at higher voltages and higher insulation stress levels, it has become more critical to be sure the design constraints are met in the stator bar design to minimize both partial discharge activity and corona activity involving the stator bars. The stator bar insulation system must be designed for minimum partial discharge activity and ideally is corona free at the stator winding operating stress levels, and at the operating conditions (temperature and pressure) the generator is subject to. This paper will present the findings associated with the development work in designing, testing and implementing a PD reduced and corona free design.     

Leakage behavior of DC electrically degraded (Ba,Sr)TiO/sub 3/ thin films

The phenomena of dc electrical degradation of (Ba/sub 0.5/Sr/sub 0.5/)TiO/sub 3/ thin films was studied. From our experimental and analytical results of current versus voltage (I-V) characteristics, it was shown that the degraded devices exhibited analogous leakage behaviors with the devices which have thin intercalated (Ba/sub 0.5/Sr/sub 0.5/)TiO/sub 3/ layers with intentionally introduced oxygen vacancies between cathodes and thick (Ba/sub 0.5/Sr/sub 0.5/)TiO/sub 3/ layers without intentionally introduced oxygen vacancies. This could be explained by assuming that oxygen vacancies accumulate at the interfaces between the cathodes and the (Ba/sub 0.5/Sr/sub 0.5/)TiO/sub 3/ films after fatigue.