燃气蒸汽联合循环机组性能变化探讨

文章介绍了某电厂PG9351燃气轮机在发生了压气机0级动叶断裂的故障之后,如何确定对该机组性能下降及确定机组性能下降的原因分析。     

天然酯-普通纸(或热稳定纸)绝缘热老化特性

为研究新型绝缘油天然酯与两种绝缘纸组成的酯-纸绝缘热老化特性,将天然酯-普通纸和天然酯-热稳定纸绝缘试品,在90℃、110℃和130℃下进行了399 d的热老化试验.结果表明:天然酯-纸绝缘中,相同老化条件下,热稳定纸聚合度和稳定聚合度都分别明显高于普通纸;通过热稳定纸中含有双氰胺的红外光谱分析,从官能团角度研究了热稳定纸抑制绝缘老化的两大机制.热稳定纸能吸附较多糠醛;对同一种酯-纸绝缘,糠醛仍可作为衡量变压器中酯-纸绝缘老化程度的参量;对不同绝缘纸的酯-纸绝缘,糠醛含量的差异不能表征它们之间绝缘纸老化程度的差异.研究了这两种不同酯-纸绝缘老化过程中,酯中微水含量变化规律的异同,从而建议使用天然酯的变压器,用热稳定纸作为与之匹配的固体绝缘材料,以利于酯在老化过程中保持较好绝缘性能.     

Outdoor HV composite polymeric insulators

HV composite polymeric insulators are being accepted increasingly for use in outdoor installations by the traditionally cautious electric power utilities worldwide. They currently represent ~60 to 70% of newly installed HV insulators in North America. The tremendous growth in the applications of non-ceramic composite insulators is due to their advantages over the traditional ceramic and glass insulators. These include light weight, higher mechanical strength to weight ratio, resistance to vandalism, better performance in the presence of heavy pollution in wet conditions, and comparable or better withstand voltage than porcelain or glass insulators. However, because polymeric insulators are relatively new, the expected lifetime and their long-term reliability are not known and therefore are of concern to users. Additionally they might suffer from erosion and tracking in the presence of severe contamination and sustained moisture. This leads to the development of dry band arcing that under certain circumstances could lead to failure of polymer insulators. In this paper a review is presented of the recent performance experience of HV composite polymeric insulators in outdoor service, testing methods, aging, the ranking of the materials, the role of fillers, the role of low molecular weight components present in the insulators, the mechanisms responsible for the loss and recovery of hydrophobicity, one of the most important properties of polymers, the mechanisms of failure, detection of faults, type and quantity of natural contaminants, effects of exposure to rain, hydrocarbons, stationary air and wind, various methods to optimize the electrical performance and a relatively new method for evaluating the performance status of polymeric insulators in the field     

Electrical and environmental aging of silicone rubber used inoutdoor insulation

This is a laboratory study on the aging of SIR and hydrophobicity recovery. UV radiation, corona discharges, acid rain and dry-band arcing are employed as sources of the aging. Chemical and morphological analysis is used to detect the surface chemical and structural changes derived from these stresses. The nature of highly mobile low molecular weight (LMW) chains achieving a quick recovery of the hydrophobicity is carefully examined. Their generation and extinction caused by these stresses are investigated. From this study, it is shown that oxidation that induces crosslinking, branching, interchanging and a formation of silanol groups are the most dominant chemical reactions during the aging of SIR. Furthermore, silanol groups that are byproducts of oxidation restrict the diffusion of mobile LMW chains, which decreases the recovery speed of hydrophobicity and accelerates the aging. A typical aging scenario of SIR from the installation to the end of their life is drawn     

油纸绝缘老化特征产物生成速率研究

变压器绝缘老化是影响电网稳定运行的重要因素之一。通过实验室加速老化试验并结合现场实际,对油纸绝缘的老化特性和机理进行研究,从而为变压器绝缘状态评估和寿命预测提供依据和参考。该文针对处于老化中后期不同初始老化程度的油纸绝缘,在80和130 ℃下对老化特性进行研究,得到各老化程度特征产物随老化时间的变化关系,并对老化特征产物的生成速率进行分析。结果表明：在该文的试验条件下,处于老化中后期的油纸绝缘,在后期继续老化过程中特征产物的生成速率随油纸绝缘初始老化程度的增加并不呈现递增趋势,而是成近似指数递减关系,这与纤维素绝缘纸降解过程中断键(葡萄糖单体间糖苷键)速率的变化一致。     

复合绝缘子憎水性机理分析

本文阐述了老化前后复合绝缘子表面憎水性的变化，分析了复合绝缘子老化的原因，并通过试验验证了复合绝缘子憎水性丧失及恢复的机理。     

合成绝缘子材料的TSC试验研究

通过采用热刺激电流法对合成绝缘子材料进行热刺激电流(TSC)的探索性对比测试,力图探索热刺激电流法在评价合成绝缘子特性中的应用可能性.文中对比了同一厂家的两批合成绝缘子试样的TSC特性,初步的试验发现,新旧合成绝缘子之间的TSC测试结果是明显不同的,结合试样的憎水性试验以及微观结构的分析,表明TSC测试结果在一定程度上能够与合成绝缘子材料的老化联系起来.通过深入系统的研究合成绝缘子的TSC特性和合成绝缘子材料的老化特性之间的关系,将能够为合成绝缘子老化特性及老化程度的评价提供新的方法.     

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     

憎水性清洁剂对电气设备外绝缘的影响

积污老化是造成电气设备外绝缘性能下降的主要原因之一,目前主要采用酒精擦洗的方法进行处理,效果并不理想。为此,介绍了一种具有清洁功能的憎水清洁剂,它能够实现对老化硅橡胶表面深度交联污秽的彻底清洁,同时通过残留憎水性保护膜提升设备的绝缘阻值。针对积污老化对复合绝缘子憎水性及绝缘阻值的影响以及清洁剂在污秽清洁、憎水提升和绝缘电阻恢复等方面的性能进行了实验和理论分析。初步研究表明:积污老化严重降低复合绝缘子在高温高湿环境下的外绝缘性能;新型清洁剂具有比酒精更为优异的污秽清洁能力,同时残留保护膜可以明显提升材料表面的憎水性和绝缘电阻,为高湿条件下绝缘检测提供了一种可供选择的解决方案。     

Condition Evaluation for Aging State of Transformer Oil-paper Insulation Based on Time-frequency Domain Dielectric Characteristics

For the oil-impregnated power transformers in service, the condition of the main insulation system is very important. This article reports a non-destructive evaluation technique based on time-frequency domain dielectric characteristics. First, the polarization/depolarization current and frequency-domain spectroscopy were well measured under controlled laboratory conditions. Then, the recovery voltage curves and recovery voltage polarization spectroscopy were also obtained by using the conversion method between polarization/depolarization current and recovery voltage based on the extended Debye model. After that, the time-domain dielectric characteristics, which can represent oil-paper insulation aging, were extracted from the polarization/depolarization current curves, recovery voltage curves and recovery voltage polarization spectroscopy. In addition, the frequency-domain dielectric characteristics, which can represent the oil-paper insulation aging, were also proposed in terms of frequency domain spectroscopy. Finally, the change rules of time-frequency domain dielectric characteristics under different aging times were investigated in depth. Results show that the time-frequency domain dielectric characteristics are sensitive to the aging states of power transformers, which could be utilized to diagnose the aging state of oil-paper insulation in field power transformers.     

Interfacial phenomena in composite high voltage insulation

This paper deals with two different types of composite insulating materials for HV outdoor insulation technology. For outdoor applications fiberglass reinforced polymer (FRP) is used mainly in transmission line insulators (composite long rods), and as power apparatus housings (composite hollow core insulators). During the last decade mineral filled polymer (MFP) was found to be very suitable for outdoor insulation in the medium and HV ranges. To meet the outdoor demands, long-term stability and durability against environmental stresses are necessary. Composite insulation consists of more than one dielectric component, and linking at least two different kinds of materials leads to interface problems. These regions always appear as weak material structures that can be attacked by various aging mechanisms. The long-term performance and aging resistance are determined by the interface quality. One can distinguish four principal kinds of interface: microscopic, e.g. those between fillers and matrix components; macroscopic, e.g. those between glass fiber rod and polymeric shielding material; internal, in the insulation bulk; and external, solid surface against a liquid or gaseous phase. Today the use of composite insulating materials in HV technology is state of the art. They offer a wide range of superior properties for indoor as well as for outdoor applications. Further improvements should focus on the hydrophobicity and on the long term resistance of the external interface and the stability of the internal interface     

碳纤维复合芯导线综合因素老化试验方法的研究

近年来,输变电领域出现了一种可以替代传统钢芯铝绞线的新型碳纤维复合芯导线。导线长期暴露于野外,运行环境复杂,碳纤维复合芯在电压、拉力、扭力、自然环境老化等综合作用下的性能可能会大大降低甚至失效。文章提出一种试验方法,通过综合因素老化试验模拟导线的现实工况下的老化,为以后碳纤维导线运行性能分析作为实验论证,期望结合运行数据能够对碳纤维导线的周期寿命做出预测。     

On Improving the Running Ability of Cables with Polymer Insulation

The main factors that prevent the improvement of the running ability of electrical cables with polymer insulation have been considered. Today, compositions based on polyvinylchloride (PVC) are mainly used as polymer insulation in most electrical cables in Russia. PVC, as are most polymers, is rather sensitive to thermal aging, which is considered as one of the main reasons for the occurrence of various polymer-insulation defects that lead with time to short circuit and fire. It has been shown based on the experimental data that the sewn-in chains of polyene conjugated bonds are formed in PVS macromolecules during the thermal aging. The chains proper are the main reasons for deterioration of the dielectric properties of PVS insulation. The incorporation of conventional plasticizers like phthalates, phosphates, etc., into a polymer matrix plays a much smaller role. Thus, to develop a new generation of polymer insulation, first of all it is required to produce new types of stabilizers that can both efficiently eliminate the formed polyene conjugated carbon bonds during thermal aging and additionally improve all the physical, mechanical, performance, and technological properties of polymer insulation.     

固体氧化物燃料电池失效快速判断机理探讨

在简单综述了导致固体氧化物燃料电池(Solid Oxide Fuel Cell,SOFC)失效的主要原因的基础上,探讨了采用实验室模拟加速的实验研究和材料损伤演化动力学与计算机模拟的理论研究来对SOFC的失效进行快速判断的可行性。     

Hydrophobicity loss and recovery of silicone HV insulation

Most of the silicone materials used for HV outdoor insulation are high-consistency, heat cured polydimethylsiloxane (PDMS) elastomers. The unique properties of PDMS that make it suitable for HV applications are reviewed. The surface of these elastomers can be rendered hydrophilic by exposure to discharges. A time and temperature dependent hydrophobic recovery ensues when exposure ceases. A variety of surface characterization investigations have established that corona exposure forms a brittle, wettable, silica-like layer on the surface of most PDMS elastomers. This is consistent with similar effects from oxygen and inert gas plasma treatment. There is still considerable debate as to the relative importance of the two major mechanisms postulated to account for the hydrophobic recovery after corona discharge. The diffusion mechanism invokes migration of low molecular weight species from the interior to the surface, while the reorientation or overturn mechanism envisages a surface reorganization with polar entities such as silanol groups resulting from surface oxidation rotating away and being replaced by methyl groups in the outermost surface layers. In our view, the highly crosslinked silica-like layer cannot reorient readily between hydrophilic and hydrophobic states at the surface, suggesting that diffusion of low molecular weight PDMS components is the more important mechanism of hydrophobic recovery. Recent data obtained on PDMS samples free from low-molecular-weight diffusible species show that hydrophobic recovery may be due to in-situ depolymerization     

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     

Inception and propagation mechanisms of water treeing

Mechanisms of water treeing are reviewed. A definition of water trees is proposed on the basis of permanent the hydrophilic character and the reduced breakdown strength. Properties are discussed that are relevant to the water tree definition and to the inception and propagation mechanism. This includes the water content, the (sub)micrometer structure and the dielectric properties. The discussed propagation mechanisms include electro-mechanical forces, diffusion of hydrophilic species and two types of oxidation mechanisms. Also attention is paid to the correlations between processes and aging conditions. Inception mechanisms include injection of hydrophilic species and/or oxidation in damaged regions, electro-mechanical damage due to high electrical fields     

Evaluation of medium voltage enameled wire exposed to fast repetitive voltage pulses

The paper describes the investigation of the failure mechanisms of medium voltage inter-turn insulation, as a consequence of pulse aging. To study the performance and failure behaviour of enameled wires, models of inter-turn insulation are prepared with enameled wires having polyimide and nano-filled coatings. The aging of such bar samples is attained by sinusoidal (60Hz), fast repetitive unipolar voltage pulses, and high frequency AC waveforms. To establish the residual strength of the bar samples, DC breakdown voltages are determined before and after the aging. In addition, the thermally stimulated depolarization current (TSDC) is used to provide information about the relaxation processes, such as the disorientation of the dipoles and the release of charges from the trapping sites in enameled wires. The various trapping levels, which have discrete energy differences with distinct peaks in the thermograms, are discussed in terms of space charge polarization     

用红外光谱研究室温硫化硅橡胶电晕老化及寿命估计

电晕是引起室温硫化硅橡胶(RTV)老化的重要因素之一,因此对RTV进行了电晕老化试验,并利用傅立叶变换红外光谱(FTIR)分析了RTV的电晕老化性能,比较了不同材料RTV的电晕老化性能,试验结果表明,纳米材料可以明显改善RTV的电晕老化性能。还分析了纳米材料提高RTV抗电晕性的机理,利用基于陷阱理论的聚合物电老化寿命公式及电晕老化前后材料的红外光谱变化评估了RTV的寿命,纳米材料能使RTV的电晕老化寿命提高到3～4.9倍。此方法可为定量评估有机绝缘材料寿命提供参考。     

Dielectric breakdown of epoxy-based composites: relative influence of physical and chemical aging

The effect of aging on the dielectric strength of epoxy-inorganic particle composites used for insulators in the high voltage industry is reported. A differential scanning calorimetry analysis of an insulator aged twenty years in actual service conditions indicated both a chemical degradation and a structural recovery of the polymer network. This composite exhibited however a breakdown field comparable to that of a fresh sample with the same formulation. An accelerated physical aging was thus performed which lead to a large increase in the high voltage performance of the newly processes composite over time. This improvement was attributed to a densification of the thermoset resin, which impeded tree growth. It was also observed that the choice of the electrode geometry greatly alters the measurements under high electric field. In a quasi-homogeneous field configuration, the breakdown was mainly governed by the major flaws at the sample scale, namely the reinforcing particles. On the contrary, under a divergent field (with a point-plane electrode arrangement), the field was essentially localized at the point electrode tip, and the major flaws might not be reachable by the damage tree. It hence appeared that the measurements performed in a quasi-homogeneous field are not very sensitive to the variations within the polymeric matrix as are the measurements under a divergent field.