功率变压器老化和延寿中英对照

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1、功率变压器老化和延寿便携式-电力变压器是一个关键的和任何电力公共事业昂贵的资产,世界各地许多变压器的电弧服务接近或超出其设计的范围。有一种日益注重扩展现有变压器维护范围，以最大限度的增大投资回报率。变压器故障的统计资料展明大部分的故障发生前均达到其额定寿命。由于介质的问题而引起的变压器故障据报道高达75，在石油中出现的呋喃化合物提供了一个固体电介体恶化的指标，它很重要的对监定电介体的恶化阶段及其敏感程度的老化。老龄问题是还强烈依赖于温度，氧气和水的水平，通过控制这些变数变压器寿命能被最大化。本论文介绍了一种模糊逻辑基础的方法既使用主要指示器用于估计电力变压器的寿命，例如湿气和呋喃化合物。索引期

2、限-变压器年龄评估、寿命延长、可靠性.导言电力变压器的功率老化有到达一紧要关头的水平。接近预期寿命的现有设备是在考虑减少重要的开支当替换这些变压器费用太高时而进行的。因为大部份这些变压器正在操作超过他们的额定寿命，设备在最高负荷下面的可信度不能是确定。变压器失灵正在数字上增加而且有严重的冲击在电压、灯火管制、收入和环境中。变压器绝缘退化、加速的老化和灾难性故障发生由许多原因引起，例如极端操作的情况、不利的周围情况(高温度和湿度指数),完全故障、巨涌(转变/闪电)和地磁气的暴风雨。变压器老化总是被加速.由于缺乏维护和适当的过失诊断。绝缘系统的退化伴随着自身参数的变更或其它的行为现象。绝缘纸和油降

3、格生产的湿气和炉气为火炉常态和加速老化负责。由于过热，瓦斯在绝缘系统被释放,部分的解除(PD)和剧烈进行.同样,水分含量在降低和绝缘的失败链中担当了一个重要的角色。纤维素和油之间的含水量和它的运动是温度受扶养者。过失瓦斯的常数监听,热点温度和含水量(WC)在发现过失类型方面帮助,强烈和,直到善行范围,它的位置为止。热的情况监听变压器(包括负荷轻打变更者)台子重要的为变压器操作的计划在个别项目在最高负荷和在紧急载入。加速的老化发生由于湿气和氧水平的增加在那油。湿气和氧水平是温度受扶养者和增加与温度湿气索引(THI)的增加 .比较高度湿气和氧能领引到一泡沫能引起悲惨的失败的形成。增加的可信度变压器

4、需要对负荷和温度根据以可接受的湿气极限为基础的一个操作的标准。在有效的延寿方面分别采用严格和有效的冲击对气体处理的来源监定非常重要。对于确定类型和严重过失，用正确的解释溶解瓦斯分解(DGA)是识别的方法之一。在线 DGA 、PD和诊断对于建立资产正直非常的重要，例如在绕组运动中的频率回应分析 (FRA)、恢复电压测量(RVM)。变压器诊断和监听数据重要选定操作的标准,资产管理和可信度为寿命延长集中了维护(RCM)策略。比较好的资产管理能达到与在线监听和有效的诊断。准确性寿命评估结果对寿命延长的服务资产是必要。.变压器老化决定设备的情况和老化过程是很困难的当它包括多数变数演变同时又是一种合成物。

5、在油/纤维素绝缘系统中的老化过程是一种在热应力压迫和可测量作用力之下不能分的电介体系统的化学反应。电介体温度是引起老化的关键参数，这就是机械和电材料变化的原因。纸绝缘中包含有约40%纤维素。聚合的程度(DP)是测量每一分子链中的葡萄糖单元的平均数值。DP超过1000时，纸绝缘出现高度电介体和可拉长单元,当DP值较少的超过300时，纸绝缘出现很少的电介体和很差的机械性能。在绝缘系统中，水和氧的出现加速了老化现象。对于判断变压器的老化、可靠性和安全性湿气是一个很好的指示器。水解、热分解和氧化是三个同时进行的机理。老化机理影响着电介体和电介质的机械性能。111. 寿命评估的目标在相同的服务期内，同一

6、变压器的剩余寿命因为它的绝缘性能可能改变。绝缘性能依赖于温度、湿度和含氧量。操作环境(高度,周围情况，光照和气流),电动装置,系统阻抗,配电系统和照明巨涌(在电压之上),完全故障和污染是加速资产老化的主要因素。经济的和寿命评估的目标是必要的，为现有的老化设备计划维护、再布置或退役。呋喃化合物和水分含量是寿命评估的主要指标。火炉化合物是由起初的过失引起常态老化绝缘纸(纤维素)降格产生的。由于降格过程,纸的张力和电介体减少。由于故障电流，电磁力有严重的冲击在绝缘纸上从而降低它的可张力。好的相互关系能在呋喃化合物和化合物和聚合 的程度(DP)之间获得 .因此,出现在油中的火炉化合物的量是寿命评估的一

7、个很好的指标。变压器使用年限特征是基于呋喃化合物在不同的年限中的出现,如图 1 所示.剩余寿命 (年限)图1：有关于呋喃系的变压器老化特性(C4H4O).因年限出现的绝缘降格增强了呋喃系呋喃系产生是由于遍及所有温度的上升就像在局部的热生产过程被活性中断.基于分析，设备可能被识别由于呋喃系产生的常态老化或局部故障。用质量较差的包装纸操作设备可能造成灾难性故障连带威胁着环境和附带损害。对监视器的包装纸退化趋势,夫喃系分析在所有的评估中扮演着关键的角色。它是非常有用的诊断,决定着故障变压器是否应该修复,还是出现了再创伤或扔弃。温度、氧和湿气在加速老化的过程中是主要因素。操作温度和周围温度在变压器的使

8、用周期内始终存在,影响绝缘寿命。研究和经验领域表明逐渐增加温度将减少设备最大负荷绝缘的寿命。在常态操作温度下,每上升7设备将减少50%的寿命.由于包装纸热电运动的降格,在绝缘链中生成了湿气(含水量)倒不如老化油。在大气出现的潮气穿透过弱的密封剂改变气压梯度。在变压器中的水可溶性矿物油增加伴随着温度的增加。湿气影响分子链分解,加速纤维素老化过程,非同一般的张力和电介体设备的绝缘系统。介质击穿浓度伴随着湿气增加。基于在绝缘链中出现湿气，变压器风险评估对它的有效寿命延长和比较好的设备管理是必要的,如表1所示.表 1 湿气消除及变压器失灵危险区域绝缘平均湿度评估4%进入危险地域5%6%相当多的失灵风险

9、7%即将出现的失灵湿气在包装纸和油之间交换和它的动力学是高度地依靠温度。从包装纸到油的湿气动力学增加伴随着温度的增加,但是湿气返回到包装纸时却伴随着温度的缓慢的减少。为测量在油中的湿气,标准方法是 Karal Fischer 反应测试(美国材料试验学会 D 1533).这个测试由于它的高选择性和敏感被高度地推荐而且广泛地使用。绝缘系统的含水量应该保持最小量到维持必需的电介性能。变压器老化特性基于不同的寿命周期内出现的含水量,如图 2 所示.剩余寿命 (年限)图 2:由于老化和热电磁-动力的降格出现的变压器老化特性用湿气的增加量表示IV.基于模糊逻辑的寿命判断模型通常夫喃系和湿气同时地以最复杂的

10、模式被产生而且是在识别设备的剩余寿命方面是主要因素。两者的出现在设备性能和寿命方面有严重的冲击,不理睬一可以误导判断。模糊逻辑模型和分析被逐渐实行获得比较好设备剩余寿命判断。图 3&4表示的是湿气和夫喃系为输入变量时的寿命评估模糊逻辑模型。图 5表示的是设备的使用周期当做输出变量时的模型。输入变量 湿气 图 3: 输入变量“湿气”(成员函数)为变压器年限模型输入变量 夫喃 图 4: 输入变量“夫喃”(成员函数)为变压器年限模型Mamdani的模糊推论方法是用来对设备的寿命估计。 (1)x 是和 y是,或x是和y是,在此是关联的含义.如果x是及y是，然后z是 (2)x表示湿气,y表示夫喃系作为输

11、入(变量)和z为变压器的老化程度而且是输出变数。, , 表现他们各自的功能。规则范围限定在: AND (3)在模糊设置中，是x在的全体值集合而是y在的全体值集合。输出变数 年限 图 5: 输出变量年限(成员函数)综上所述由于易受影响的输出量(设备寿命)，地心引力运算法则集中用来计算区域Ai和中心区域每元函数(MF)的mi. (4)在此： (5) (6)使用上面的模型,易受影响的输出量既变压器寿命是关于湿气和夫喃系的已被确定和描述在了图6中.图 6:变压器年限模型, 以湿气和夫喃系当做输入变量为基础V.寿命延长现有变压器数量的寿命延长是一个重要实效的议题。有足够的安全性和涉及操作老化单位方面的环

12、境风险接近外面的监视和评估的载入极限。利用正确及时的评估可以控制老化过程, RCM申请和适当的操作标准落实了广大的剩余寿命与可接受的安全性和可改良的可靠性能达到比较好的有成本效益的利用。经典的诊断用现实做解释，因此RCM对设备延长寿命是至关重要的。通过贯彻适当的操作标准(动力载荷)可以改良现有老化设备的利用和有效率的/有效的维护对维持/升级绝缘系统。由于它在强调失败结果方面定义了失败的问题根源，利用RCM能完成比较好的结果。如图7流程图中所表示，利用RCM可以有效地实现设备延长寿命.RCM有助于经济有效的维护，方便操作,增强安全性而且减少环境的风险。基于在线监听和诊断,倘若可能寿命延长的RCM

13、策略能被比较好实现。-设备的关键部件和他们各自的功能已经完全已知。-设备的可能故障和他们的结果包括所有的系统已知已知，如输出变量,被迫的储运损耗(中断),收入,修理,再磨光,替换费用、安全和环境的连带损害。 图 7: 变压器寿命延长和管理流程图VI.总结利用输入变量的湿气和呋喃化合物模糊模型可以预测纸包装变压器使用年限 。寿命判断将有助于最大化实现可实行的操作效率。系统可靠性和设备实用性能被确保，通过改良系统性能。过早的故障风险能被最小化。设备及时的翻新、替换或再布置能被规划。正确的操作和维护策略能被改进和贯彻以得到最大的回报。间接的和环境的损害能被有效地最小化。 Power Transfor

14、mer Aging and Life ExtensionAbstract-Power transformer is a critical and expensive asset for any power utility.Many transformers around the world are serving close to or beyond their designed lie.There is an increasing focus on maintenance and lie extension of existing transformers to maximize the r

15、eturn on investment.Transformer failure statistics exhibit that most of the failures have occurred before reaching their rated life.Transformer failures due to dielectric problems are reported as high as 75%.Furnace compounds presence in oil provide an indication of solid dielectric deterioration.It

16、 is important to identify the deterioration stages of dielectrics and its degree of sensitivity towards aging.Ageing is also strongly dependent on temperature,oxygen and water levels in the transformer.The transformer life can be maximized by controlling these variables.This paper presents a fuzzy l

17、ogic based approach to estimate the age of a power transformer using key indicators such as moisture and furnace compounds.Index Terms-Transformer Age Assessment,Life Extension, Reliability .INTRODUCTIONPower transformers aging population has reached a critical level.Existing assets that are close t

18、o their expected life are being considered for further utilization in order to reduce capital expenditure as the replacement cost of these transformers is too high.Since many of these transformers are operating beyond their rated life,asset reliability under peak load cant be ensured.Transformer fai

19、lures are increasing in number and having serious impact on forced outages,blackouts,revenue and environment. Transformer insulation degradation,accelerated aging and catastrophic failures occur due to many reasons such as extreme operational conditions,adverse ambient conditions (high temperature a

20、nd humidity index),through faults,surges (switching/lightning) and geomagnetic storms.Transformer aging is also accelerated.due to lack of maintenance and proper fault diagnosis.The degradation of insulation system is accompanied with the phenomenon of changing physical parameters or its behavior.In

21、sulation paper and oil degradation produce moisture and fiurnace which are responsible for normal and accelerated aging.Gases are released in the insulation system due to overheating,partial discharge (PD) and arcing.Also,the presence of moisture plays an important role in the degradation and failur

22、e of insulation chain.Water content and its movement between cellulose and oil is temperature dependent.Constant monitoring of fault gases,hotspot temperature and water content (WC) helps in detecting faults types,intensity and,up to a good extent,its location.Thermal condition monitoring of transfo

23、rmer (including load tap changer) stands vital for transformer operational planning in particular at peak load and at emergency loading.Accelerated aging occurs due to increase in moisture and oxygen level in the oil.Moisture and oxygen levels are temperature dependent and increase with the increase

24、 in temperature humidity index (THI) .Higher level of moisture and oxygen can lead to a bubble formation that can cause catastrophic failure.Increased reliability of a transformer requires an operational criterion that is based on acceptable moisture limits according to load and temperature.It is vi

25、tal to identify the sources of gassing with their respective severity and impact on the asset remnant life.Dissolved gas analysis (DGA) with accurate interpretation isone of the methods for identifying the type and severity of the fault.Online DGA,PD and diagnostics such as frequency response analys

26、is (FRA) for winding movement, recovery voltage measurement (RVM) are important to establish assets overall integrity.Transformer diagnostics and monitoring data are important to decide on the operational criteria,asset management and reliability centered maintenance (RCM) strategies for life extens

27、ion.Better asset management can be achieved with on-line condition monitoring and effective diagnostics.End of life assessment with accuracy is essential for an asset to serve for its extended life.TRANSFORMER AGINGIt is difficult to determine the assets condition and aging process as it involves ma

28、ny variables acting at the same time in a complex manner.The aging process in the oil/cellulose insulation system under thermal stress and their measurable effects are due to chemical reactions in the inseparable dielectric system.The dielectric temperature is a critical aging parameter that causes

29、a change in the mechanical andelectrical properties of the material.Paper insulation is composed of approximately 40% cellulose.Degree of Polymerization (DP) is a measurement of average number ofglucose units per molecular chain.Paper insulation,with DP greater than 1000,exhibits high dielectric and

30、 tensile properties,where as DP value less than 300 shows a paper with poor dielectric and mechanical properties.Presence of water and oxygen in the insulation system accelerates the aging phenomenon.Moisture is a good indicator to determine the aging,reliability and safety of the transformer.Hydrol

31、ysis, Pyrolysis and Oxidation are the three mechanisms,acting simultaneously.The aging mechanism affects the electrical and mechanical properties of the dielectrics.111.END OF LIFE ASSESSMENTResidual life of identical transformers,with same period of service,may vary because of its insulation behavi

32、or.Insulation behavior depends on temperature,moisture content and oxygen ingress.Operating environment (altitude,ambient conditions,sunshine and airflow),dynamic loading,system impedance,switching and lighting surges(over voltages),through faults and contaminations are the major factors towards ass

33、ets accelerated aging.Economic and end of life assessment are essential for the existing aged assets to plan for the maintenance,relocation or retirement.Furnace compound and moisture contents are the key indicators for life assessment.Furnace compounds are generated due to insulating paper (cellulo

34、se) degradation with normal aging as well as due to incipient faults.Due to degradation process,paper tensile and dielectric strength decreases.Electromagnetic forces due to through fault current have serious impact on the paper life by lowering its tensile strength .Good correlation can be obtained

35、 between furnace compound and degree of polymerization (DP).Therefore the furnace compound quantity present in the oil is a good indicator for life assessment.The transformer age characteristics based on furnace compound present in different age groups is shown in Figure 1. REMNANT LIFE ( YEARS)Figu

36、re 1 Transformer aging characteristic with respect to Furan (C4H4O).Furan increases due to insulation degradation with age.Furans are generated due to over all rise in temperature as well as due to the heat produced by active fault in any localized area.Based on the analysis,asset could be identifie

37、d for furans produced due to normal aging or localized fault.Asset operating with poor paper strength may result in catastrophic failure with serious threat to environment and collateral damages.To monitor the paper degradation trend,Furan analysis can play key role in the over all assessment.It is

38、a very useful diagnostic for assessing whether a failed transformer should be repaired,rewound or scrapped.Temperature,oxygen and moisture are the key factors in accelerating the aging process.Operating temperature and ambient temperature exists throughout the life of the transformer,affecting the i

39、nsulation life.Studies and field experience show that gradual increase in temperature reduces the peak load insulation life of the asset.A rise of 7Celsius above normal operating temperature decreases assets life by 50%.Moisture (water content) in insulation chain is produced due to thermo-kinetic d

40、egradation of the paper as well aging of the oil.Moister present in the atmosphere penetrates through weak sealant with the change in the pressure gradient.The water solubility in the transformer mineral oil increases with the increase in temperature.The moisture influences the decomposition of the

41、molecular chain,accelerates the cellulose aging process,affecting the tensile and dielectric properties of the insulation system.Dielectric breakdown strength decreases with increase in moisture.Based on the moisture presence in the insulation chain,transformer risk assessment is essential for its e

42、ffective life extension and better asset management,Table 1.TABLE IMOiSTURE LEVELS AND TRANSFORMER FAILURE RISK ZONESInsulation Average Moisture ContentAssessment4%Entering Fisk Zone5%6%Considerable Failure Risk7%Failure ImminentMoisture is exchanged between paper and oil and its dynamics are highly

43、 temperature dependent.Moisture dynamics from paper to oil increases with increase in the temperature,but with the decrease in temperature the moisture moves back to the paper slowly.The standard method for measuring the moisture in oil is Karal Fischer reaction test (ASTM D 1533).This test is highl

44、y recommended and is widely used due to its high selectivity and sensitivity.Water content in the insulation system should be kept to a minimum to maintain the required dielectric properties.The transformer age characteristics based on moisture contents,present in different age groups is shown in Fi

45、gure 2.REMNANT LIFE ( YEARS) Figure 2:Transformer aging characteristics with increase in moisture Content due to aging and thermo-kinetic degradation.IV.LIFE ESTIMATION MODEL USING FUZZY LOGICUsually furan and moisture are generated simultaneously in a very complex manner and are key factors in iden

46、tifying assets remnant life.Presence of both has serious impact on the asset performance and life,ignoring one could mislead the estimation.The fuzzy logic modeling and analysis has been carried out to get better assets remnant life estimation.Figure 3&4 represents the moisture and furans as input v

47、ariables for the life estimation fuzzy logic model.Figure 5 represents the assets age as an out put variable of the model.Input variable “Moisture” Figure 3: Input variable “Moisture” (membership functions)for transformer age model Input variable “Furan” Figure 4: Input variable “Furan” (membership

48、functions)for transformer age model Mamdanis fuzzy inference method is applied to estimate the assets life. (1)Where x is and y is ,or x is and y is and so on as a conjunction of implications.IF x is AND y is， THEN z is (2)Where x represents the moisture,y represents furan as inputs (variables) and

49、z the age of the transformer and is the output variable. ,then represent their respective membership functions.The extent to which a rule is activated: AND (3)Where is the membership value of x in the fuzzy set and is the membership value of y in the fuzzy set.output variable “Age” Figure 5: output

50、variable age (membership functions)Defuzzificarion:For crisp output (asset life),center of gravity algorithm is used to calculate the area Ai and center of area Mi for each member function (MF). (4)Where: (5) (6)Using the above model,the crisp output transformer age with respect to moisture and fura

51、n is determined and is represented in Figure 6.Figure 6:transformer age model,based on moisture and Furan as input variablesV.LIFE EXTENSIONLife extension of existing transformer population is an important issue for the utilities.There is an ample safety and environmental risk involved in operating

52、aged units close to loading limits with out surveillance and assessment. Aging process can be controlled with accurate in time assessment,RCM application and proper operational criteria implementation Extended residual life with acceptable safely and improved reliability can be achieved with better

53、cost-effective utilization.Good diagnostics with realistic interpretation and accordingly RCM stands vital for the assets extended life.The existing aged assets utilization can be improved by implementing proper operational criteria (dynamic loading) and efficient/effective maintenance to maintain/u

54、pgrade the insulation system.Better results can be achieved with RCM as it emphasis on the failure consequence by defining the root causes of failure.With RCM assets life extension can be achieved effectively as given in the flow chart in Figure 7.RCM facilitates cost effective maintenance,better op

55、eration,enhanced safety and reduced environmental risk.Based on online monitoring and diagnostics,RCM strategies for life extension can be better achieved provided.-Assets critical components and their respective function are fully known.-Assets possible failures and their consequences including ove

56、r all system are known such as output,forced outages ,revenue,repair,refurbish,replacement cost,safety and environmentalcollateral damages.Figure 7: transformer life extension and management flow chartVI.CONCLUSIONSIn this paper transformer age has been predicted using fuzzy model with moisture and

57、furan compound as input variables.Life estimation will help in achieving maximum practicable operating efficiency.System reliability and plant availability can be ensured with improved system performance.Premature failures risk can be minimised.Asset timely refurbishment,replacement or relocation can be planned.Correct operational and maintenance strategies can be developed and implemented to have maximum retum. Collateral and environmental damages can be restricted to minimum.