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     

气压对发电机定子线棒端部电晕放电特性的影响(英文)

According to the mechanism of corona discharge at the end of the generator stator bar,a model of stator bar end corona discharge is presented.In a closed corona cage at low atmospheric pressure,the corona discharge characteristics of the stator bar end model were observed using an ultraviolet imaging instrument and an oscilloscope.The influence of atmospheric pressure on the corona inception voltage and discharge intensity was analyzed.The results show that the corona inception voltage is lower under lower atmospheric pressure;the discharge intensity is stronger under lower atmospheric pressure.The particles swarm-optimized support vector machine was employed to analyze the impacts of air pressure and humidity on the corona inception voltage.Error between the calculated value of the established model and the experimental value is less than 5%.The established model can be used to calculate the corona inception voltage of the stator bar end model.     

Investigations into the effect of humidity on stator winding partial discharges

Online partial discharge (PD) testing has become a powerful tool to plan the maintenance of stator windings of high voltage motors and generators. Interpretation of PD data is best done by monitoring the trend in PD over time. Unfortunately the trend in PD is sometimes difficult to ascertain, especially if the humidity within the stator is variable over time. This paper shows several examples of how PD is affected by humidity in operating machines. Laboratory experiments were also performed to duplicate this phenomenon. In most practical situations, it appears that the PD activity decreases as the humidity increases.     

直流下局部放电序列信号检测与特性分析

介绍了用于分析直流下局部放电序列信号的时间等待恢复模型及其假设,总结了基于基本参数放电幅值q和放电时间点t用于分析直流局部放电序列信号的多种放电谱图。利用自行研制的直流局部放电宽带检测系统获取了缺陷模型(空气中电晕、油纸绝缘的尖板、内部缺陷和沿面放电)在直流电压下的大量局部放电脉冲波形-时间序列。并对获取的脉冲波形-时间序列,使用脉冲群快速分类技术进行随机干扰脉冲剔除。在上述工作基础之上,进行了直流局部放电幅值-时间序列信号的相关性统计分析,给出了各缺陷模型对应的典型q-t、n-q、n-Δt和qsuc-q等多种直流局放谱图。试验结果分析表明,四种典型缺陷具有各自的放电特性,直流下局部放电发展过程符合时间等待恢复模型及其假设。这为基于幅值-时间序列的直流局放检测、识别提供了理论和试验依据。     

Assessment of insulation condition of generator stator bars based on velocity of ultrasonic waves

The velocity of ultrasonic waves, which were launched using the pulse-echo method and propagated in a stator insulation, was measured to assess the insulation condition of the stator bars. A statistical minimum velocity (V/sub min/) and a statistical average velocity (V/sub av/) were computed for a new and three sets of stator bars which were in operation for 16, 18 and 23 years. After velocity measurements, several conventional electrical parameters such as dissipation factor, capacitance, and partial discharge were measured, and microscopic examinations of dissected insulation of tested bars were examined with a scanning electron microscope and an optical microscope. Experimental results showed that V/sub min/ and V/sub av/ decreased and more microscopic defects were formed in the insulation with increasing operating time of the stator bar. For the three sets of aged stator bars, the insulation conditions based on Y/sub min/ and V/sub av/ were consistent with those assessed by measuring electrical diagnostic parameters. Therefore, Y/sub min/ and V/sub av/ were used to assess the insulation condition of large generators. The measurement of ultrasonic waves may offer a broad prospect for stator insulation diagnosis.     

基于数字局部放电检测的大型电动机主绝缘老化特性的研究

大型电动机在长期的运行过程中,要遭受电,热,机械等多因子应力的联合作用,使主绝缘逐渐老化,为了研究主绝缘老化机理,评估其剩余寿命,需要对电动机定子线棒进行多因子应力综合老化试验,并寻找能反映主绝缘老化程度的特征参量;本文采用先进的数字局部放电检测技术对不同老化阶段的试样线棒进行了综合测试,分析了局部放电各参量与试样线棒老化程度的关系,给出了各种反映绝缘老化特性的指纹图形,测试结果表明,随着试样线棒的进一步老化,局部放电量,放电次数,放电能量呈增长趋势,最大放电脉冲相位产生偏移,其偏斜度由大变小,这为评定大型电动机主绝缘的剩余寿命提供了参考依据。     

冲击电压下500 kV油浸倒置式电流互感器局部放电特性研究

为了研究油浸式电流互感器在运行过程中的局部放电特性,搭建500 kV油浸倒置式电流互感器在冲击电压下的局部放电试验回路,对试品施加标准雷电冲击电压和操作冲击电压,使用安装在试品末屏接地引下线处的非接触式高频局部放电传感器采集局部放电信号,通过高采样率示波器显示放电波形。在冲击试验后进行工频局部放电测量、油中溶解气体成分分析、高电压介质损耗因数测试、频域介电谱测试,以检测试品的绝缘状况。研究结果表明:油浸式电流互感器在冲击电压下发生局部放电,绝缘损坏,放电熄灭电压低于正常运行电压,放电无法自熄灭,长期累积作用造成设备故障。     

空气中电晕放电与绝缘液体中流注放电的测量和分析

Insulation is one of the most important parts in a high voltage equipment.There are gaseous,liquid and solid insulations which are commonly used.In a high voltage transformer for example the insulating materials are all used.During operation of a high voltage equipment high electric stress may occur.Under extreme condition failure of the insulation may take place.Excessive electric field in air may cause corona discharges while in liquid insulation discharges may take place in the form of streamer.This paper reports experimental results on the corona and streamer discharges in air and silicone oil.The discharges were artificially generated around a needle tip in a needle-plane electrode system with gap length of 4 mm under sinusoidal and triangular voltages.The needle was made of steel with tip radius of 3 μm and curvature angle of 30°.The needle was made by Ogura Jewelry.The discharge pulses were measured using personal-computer based partial discharge(PD)measurement system with sensitivity of better than 0.5 pC.The system is able to measure discharge in time sequential.Phase-resolved analysis of the discharges was done to interpret the physical processes behind the discharges.The experimental results showed that corona discharges took place at negative half cycles.The discharges were concentrated around 270° of phase angle of applied voltage.The discharge magnitude and discharge number of corona clearly dependent on the instantaneous of applied voltage.These were strongly supported by the application of triangular voltage.Streamer discharges occurred at both positive and negative half cycles.The discharges pulses concentrated around the peak of applied voltage at phase angle of 90° and 270°.Experimental results under sinusoidal and triangular voltages revealed that streamer discharge magnitude as well as probability of occurrence was strongly dependent on the instantaneous applied voltage.     

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。     

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.     

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.     

Understanding surface partial discharges in HV coils and the role of semi-conductive protection

An electrical insulating system in high voltage rotating machines is subjected to several stresses that cause changes of material properties during its lifetime. This phenomenon reduces progressively ability of the insulation to withstand the service stresses. Internal partial discharges can be located inside the high voltage insulation and usually they are dangerous for life-cycle duration. Surface discharges are generated at the solid/air interface in the gaps of machine stator slots or at the slot exits. Surface discharges can cause more intensive deterioration of the insulation, accelerate aging processes and definitively take aim toward premature failure of the machine. The application of conductive or semi-conductive protection layer provides certain protection for solid insulation from these discharges. Semi-conductive corona protection tapes are used on the coils at the slot exit region to electrical field control and prevent surface discharges. Laboratory measurements of the surface partial discharge quantities in specimens of high voltage coils with mica insulation were performed. The aim of the paper is to describe theoretically the development of surface discharges in rotating machines and to present surface partial discharge development in HV motors when semi-conductive layer protection is missing. The results can be found useful to understand better the surface discharge development and importance of high-quality semi-conductive protection technology.     

Unusual PD pulse phase distributions in operating rotating machines

The position of partial discharges (PD) with respect to power frequency phase position has long been known to provide useful information on the nature of deterioration of electrical insulation. In the past, virtually all such data has been from PD tests performed in the laboratory on static models or equipment. Improvements in the past 15 years in noise elimination technology have made it possible to monitor the PD activity (number, magnitude and phase position) in the HV stator windings of operating motors and generators. Over a two year period, the PD activity was recorded on more than 100 motors, hydrogenerators and turbine generators, and the pulses analyzed with respect to the ac phase position, with a resolution of 3.6°. In the majority of stator windings, the PD pulses occurred in the expected portion of the ac phase, i.e. Between 0 and 90° as well as between 180 and 270°. However a significant number of instances were recorded where the pulses appeared to be shifted ~30°. This is probably due to the phase-to-phase electric stress which occurs in the endwinding portion of a three phase stator winding. In many other machines, the PO phase positions were very different from the expected patterns determined from static tests. In some of these cases, such results were obtained on machines with suspected loose stator windings. It seems reasonable to conclude that the unusual PD patterns may be due to the influence of moving stator coils on the PD patterns. Such an influence is not easy to simulate in static laboratory tests. PD pulse phase analysis is shown to be a useful means of helping to determine the main deterioration mechanisms of stator insulation systems of operating motors and generators     

三峡右岸全空冷水轮发电机关键技术研究

介绍了三峡右岸全空气冷却水轮发电机的重要设计与制造技术。探讨了通风冷却系统设计和发电机温度场的计算,进行了通风模型的试验研究,并对发电机通风冷却进行了优化设计。在绝缘技术上,采用增大导线圆角半径等措施,提高了线棒角部电场的均匀性,采用薄型全固化新型玻璃丝带并一次成型的定子线棒槽部防晕结构及多胶模压体系制造的定子线棒,使主要电气性能指标和电老化寿命优异。机组运行结果表明,全空气冷却方式和独特的绝缘工艺等达到了设计要求,为三峡右岸水轮发电机研制提供了有益的指导。三峡右岸700 MW水轮发电机上应用的全空气冷却方式和独特的绝缘工艺等技术代表了700 MW 水轮发电机技术的发展趋势。     

13.8kV水轮发电机圈式定子绕组的端部绝缘

分析了圈式定子绕组端部的局部放电情况,提出了加强端部绝缘整体性、减小气隙、提高起晕电压及合理选择绝缘间隙等一系列措施。它应用于13.8kV水轮发电机圈式定子绕组中。     

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。     

Partial discharge and dissipation factor behavior of model insulating systems for high voltage rotating machines under different stresses

This article describes the change in partial discharge (PD) pattern of high voltage rotating machines and the change in the tan /spl delta/ as a function of the applied test voltage during the aging processes as caused by the application of different stresses on stator bars. It also compares the PD patterns associated with internal, slot, and end-winding discharges, which were produced in well-controlled laboratory conditions. In addition, the influence of different temperature conditions on the partial discharge activities are shown. The investigations in this work were performed on model stator bars under laboratory conditions, and the results might be different from those obtained for complete machines, as rotating machines are complex PD test objects, and for example, the detected PD signals in a complete machine significantly depend on the transmission path from the PD source to the measurement device.     

直流下油纸绝缘中局部放电脉冲典型波形及其参数提取

笔者介绍了直流下局部放电脉冲波形测量系统的组建以及测量电阻的校验。利用该试验系统对模拟换流变压器油纸绝缘的5种典型缺陷模型进行了局放脉冲波形测量。试验结果表明:直流下油纸绝缘中缺陷放电稳定,脉冲波形无振荡分量和过冲,且不随电压变化而发生畸变。在对典型脉冲波形进行预处理的前提下,使用形状参数法、自相关函数法、AR模型参数法以及Renvi信息量进行了波形特征参数提取。所得结果为深入研究直流下油纸绝缘中局部放电机理、局放在线监测系统的频率特性以及放电类型的波形识别提供了实验依据。     

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。