论文（设计）基于力学损耗和介质损耗参数分析大型发电机主绝缘的老化特征.doc

基于力学损耗和介质损耗参数分析大型发电机主绝缘的老化特征 贾志东1，郝艳捧1，蒋雄伟1，谢恒1，耿瑞香2         （1西安交通大学电力设备与电气绝缘国家重点实验室，陕西省西安市710049； 2太原电力高等专科学校电力系，山西省太原市030013）摘要：大型发电机的主绝缘是发电机的重要组成部分之一，大型发电机的可用性和剩余寿命在很大程度上取决于主绝缘的状况。目前，大型发电机主绝缘普遍采用环氧云母绝缘体系。针对发电机运行中主绝缘的老化情况，选用环氧云母体系绝缘材料，进行了电热应力联合作用下和热机械应力作用下的老化实验；采用新的分析方法动态力学分析法测试了不同老化时间的绝缘材料的老化特性，并且将动态力学参数与介质损耗参数作了比较；从而提出了用动态力学参数表征环氧云母绝缘老化的新方法。关键词：发电机主绝缘；动态力学特性；介质损耗；老化 1引言大型发电机的主绝缘（定子绕组绝缘）是发电机的重要组成部分之一，大型发电机的可用性和剩余寿命在很大程度上取决于主绝缘的状况。发电机运行过程中，主绝缘在电、热、机和热机应力的联合作用下，绝缘性能会逐渐下降，最终导致失效。因此加强定子绕组绝缘材料老化性能的研究对提高大型发电机的安全运行有着重要的指导意义。大型发电机的主绝缘大多采用环氧云母复合绝缘体系。为了对电机主绝缘的剩余寿命做出正确的评估，许多国家开展了寻求电机主绝缘老化特征量的研究。KenKimura等人提出了主绝缘的剩余击穿电压与介质损耗增量、最大放电量具有某种相关性1；YJKim基于局部放电评估了主绝缘性能，并且提出了新的诊断参数动态滞留电压2。但这些研究主要是基于实验数据的统计处理，没能给出令人信服的理论解释。本文从环氧云母绝缘材料的结构着手，分析了环氧云母绝缘材料分别在电热应力和热机械应力作用下的老化特性；引入了新的分析方法动态力学分析法；并且将动态力学参数与介质损耗参数作了比较，提出了用动态力学特性表征环氧云母绝缘老化特征的新方法。2发电机主绝缘的老化机理目前，大型发电机采用的环氧云母主绝缘是以云母为基础、环氧树脂为胶粘剂、玻璃布补强的热固性绝缘体系。发电机运行过程中，主绝缘会受到电、热、机械应力的联合作用；在电机的起停过程中，绝缘还会受到热机械应力的作用。在这些应力的作用下，由于环氧树脂为有机物，其老化性能比云母和玻璃丝带要差。使得环氧树脂性能下降，破坏了与其它材料的界面结构，产生气隙，诱发局部放电，绝缘性能下降，最终导致绝缘失效，图1是发电机绝缘老化的示意图。3老化分析的基本原理31动态力学分析基本原理动态力学分析是在程序控制温度下，测量高聚物质在按正弦函数变化的应力作用下的有关动态力学性能（如储能模量、力学损耗和动态粘度）随温度和频率变化的一种技术3。动态力学性能与聚合物的结构和分子运动有密切联系，是聚合物的一项很重要的力学性质。当聚合物在正弦变化应力的作用下，应力与应变关系中将会出现应变滞后于应力的现象，滞后效应是动态力学分析的基础。表征聚合物动态力学性能的主要参数有：E：储能模量，单位GPa，表示材料在形变过程中，由于弹性形变储存的能量；tan：力学损耗因子，表示以热形式逸散的能量与储存能量之比，它表示材料在形变过程中本身损耗能量的能力；：动态粘度，单位MPa·S，表示材料在形变过程中粘度的变化情况。        聚合物的结构复杂，具有多重结构运动单元，在E或tan和动态粘度随温度变化的关系曲线上将出现一系列峰，因而动态力学分析是研究聚合物结构、分子运动和性能的一种有效手段。图2是典型高聚物的动态力学温度谱。在聚合物基复合材料中，由于界面相的结构与聚合物基体和填料的结构不同，因而它对复合材料的动态力学性能有较大的影响。界面对复合材料动态力学性能的影响可以通过改变聚合物的玻璃化转变（转变）及阻碍聚合物大分子链侧基旋转或主链局部运行间接地表现出来；也可通过复合材料储能模量和动态粘度的变化来表征界面的粘结强度，因而动态力学分析也是研究复合材料结构、分子运动、界面状态和性能的一种有效手段。在分析发电机主绝缘时，环氧树脂为基体，云母和玻璃布为填料，该材料可以看作是“环氧树脂界面云母”及“环氧树脂界面玻璃布”的复合体系，故可以用动态力学分析。32介质损耗分析基本原理电介质在交变电场作用下有能量损耗，1种是由电导引起的损耗，另1种是由松弛极化引起的损耗。电介质单位时间内消耗的能量，亦就是引起电介质发热的能量，称为电介质的损耗。电介质在交变电场下的这一特性可以用介质损耗角正切来表示。图3是电介质在交变电场作用下的示意图和矢量图。介质损耗一般用tanD来描述。而且tanD仅取决于材料特性而与材料尺寸、形状无关，可由实验直接测定。4实验及结果分析41实验方法大型发电机主绝缘一般采用环氧云母玻璃带半叠包模压成型的工艺结构。本文选用2 mm厚环氧云母绝缘层压板，该板为宽20 mm的环氧云母玻璃带模压而成。为了模拟在电机中的老化情况，老化实验分2种条件进行：1种为电热应力联合作用，电压为98 kV，温度为135；另1种为热机械应力作用，也即冷热循环，把样品放入烘箱中加热到135后用风扇冷却到室温为1次循环，进行多次循环，如此反复进行。 动态力学特性参数用美国TA公司983型动态力学分析仪器测试。加力方向与玻璃带平行；升温速率为5min；温度范围为室温至200；固定频率5 Hz；振幅为03 m。介质损耗特性选用日本TR10C型精密电桥测试。测试条件满足国标GB140983要求3；采用三电极系统；主要测试介质损耗随温度的变化特性。42结果与分析421储能模量图4是试样在老化条件下储能模量的变化情况。由图可知，2种老化条件下，环氧云母绝缘材料的储能模量明显下降。由于储能模量表示的是弹性形变储存的能量，储能模量的减小表明材料老化后界面的粘接能力明显减弱。                                           422动态粘度图5是试样在老化条件下动态粘度的变化情况。由图可知，随着老化时间和老化周期的延长，动态粘度峰值向高温方向移动；老化的峰值较未老化初值相比有所下降，但老化之间的差异不明显，电热应力作用峰值基本上出现在110附近，热机械应力作用峰值也最终趋向110。这可能是由于电热应力联合作用下老化速率要比热机应力下快。但是，在2种老化条件下，室温下的动态粘度值都呈递减趋势。423力学损耗图6是试样在老化条件下力学损耗的变化情况。由图可知，老化后，力学损耗的峰值变化无明显特征，但随着老化时间和老化周期的延长，峰值点向高温方向移动。老化越严重，其峰值点对应的温度值越高；前文已提到tan峰值对应的是转变，即玻璃化转变，由此可见，老化后将导致环氧云母绝缘的玻璃化转变温度升高。424介质损耗图7是试样在老化条件下介质损耗的变化情况。由图可知，老化后，试样的介质损耗峰值较未老化试样有所下降，但规律特征不明显；老化后，介质损耗的峰值点向高温方向移动，老化越严重，其峰值点对应的温度值越高。与力学损耗峰有类似的变化趋势。5理论分析51玻璃化转变表观活化能的计算Piloyan等人提出了从任意1个升温速率下的差热分析曲线计算表观活化能的方法4。文5提出了用DMA曲线计算玻璃化转变活化能的思想，本文利用其思想，采用类似文4的推导方法，从tan温度谱来计算材料的玻璃化转变的表观活化能。        在开始阶段，物质的反应速率和DMA曲线与基线偏离之间的关系为式中E为玻璃化转变表观活化能，kJmol；R为气体常数，8314JK·mol；T为绝对温度，K；A0为常数；f（）为反应速率函数，f（）（1）n，为转化率，n为反应级数，与材料本身性能有关。                                                 将式（2）代入式（1），两边取对数后得可以看出式（5）为直线方程，由斜率可求得 E。式中tan为tan曲线与基线偏离的距离，单位mm。其求取方法如图8所示。                                           52玻璃化转变表观活化能的应用运用本文计算玻璃化转变表观活化能的方法，可以得到图9所示的活化能曲线。 由图9可以看出：老化后试样的玻璃化转变表观活化能增大。这一结论与前面的结论老化后，试样的玻璃化转变温度增大相吻合。这是因为，玻璃化转变活化能表示的是材料玻璃化转变过程中所要克服的能量，玻璃化转变温度越高，则发生转变所需供给的能量也就越大，也就是说玻璃化转变表观活化能越大。 6结论（1）环氧云母绝缘材料在电热应力和热机械应力作用下会逐渐老化。老化过程中，材料的储能模量、力学损耗和动态粘度等动态力学参数发生明显变化；同时，材料的介质损耗参数也有一定的变化。     （2）环氧云母绝缘材料老化后，其储能模量明显下降；动态粘度峰值向高温方向移动，另外其室温下的动态粘度值明显下降；力学损耗峰值和介质损耗峰值向高温方向移动。（3）环氧云母绝缘材料老化后，其玻璃化表观活化能明显增大，这一理论分析与实验结果相吻合。（4）综合前面的结论，储能模量、力学损耗和动态粘度等动态力学参数可以用来表征环氧云母绝缘材料的老化特征。Editor's note: Judson Jones is a meteorologist, journalist and photographer. He has freelanced with CNN for four years, covering severe weather from tornadoes to typhoons. Follow him on Twitter: jnjonesjr (CNN) - I will always wonder what it was like to huddle around a shortwave radio and through the crackling static from space hear the faint beeps of the world's first satellite - Sputnik. I also missed watching Neil Armstrong step foot on the moon and the first space shuttle take off for the stars. Those events were way before my time.As a kid, I was fascinated with what goes on in the sky, and when NASA pulled the plug on the shuttle program I was heartbroken. Yet the privatized space race has renewed my childhood dreams to reach for the stars.As a meteorologist, I've still seen many important weather and space events, but right now, if you were sitting next to me, you'd hear my foot tapping rapidly under my desk. I'm anxious for the next one: a space capsule hanging from a crane in the New Mexico desert.It's like the set for a George Lucas movie floating to the edge of space.You and I will have the chance to watch a man take a leap into an unimaginable free fall from the edge of space - live.The (lack of) air up there Watch man jump from 96,000 feet Tuesday, I sat at work glued to the live stream of the Red Bull Stratos Mission. I watched the balloons positioned at different altitudes in the sky to test the winds, knowing that if they would just line up in a vertical straight line "we" would be go for launch.I feel this mission was created for me because I am also a journalist and a photographer, but above all I live for taking a leap of faith - the feeling of pushing the envelope into uncharted territory.The guy who is going to do this, Felix Baumgartner, must have that same feeling, at a level I will never reach. However, it did not stop me from feeling his pain when a gust of swirling wind kicked up and twisted the partially filled balloon that would take him to the upper end of our atmosphere. As soon as the 40-acre balloon, with skin no thicker than a dry cleaning bag, scraped the ground I knew it was over.How claustrophobia almost grounded supersonic skydiverWith each twist, you could see the wrinkles of disappointment on the face of the current record holder and "capcom" (capsule communications), Col. Joe Kittinger. He hung his head low in mission control as he told Baumgartner the disappointing news: Mission aborted.The supersonic descent could happen as early as Sunday.The weather plays an important role in this mission. Starting at the ground, conditions have to be very calm - winds less than 2 mph, with no precipitation or humidity and limited cloud cover. The balloon, with capsule attached, will move through the lower level of the atmosphere (the troposphere) where our day-to-day weather lives. It will climb higher than the tip of Mount Everest (5.5 miles/8.85 kilometers), drifting even higher than the cruising altitude of commercial airliners (5.6 miles/9.17 kilometers) and into the stratosphere. As he crosses the boundary layer (called the tropopause), he can expect a lot of turbulence.The balloon will slowly drift to the edge of space at 120,000 feet (22.7 miles/36.53 kilometers). Here, "Fearless Felix" will unclip. He will roll back the door.Then, I would assume, he will slowly step out onto something resembling an Olympic diving platform.Below, the Earth becomes the concrete bottom of a swimming pool that he wants to land on, but not too hard. Still, he'll be traveling fast, so despite the distance, it will not be like diving into the deep end of a pool. It will be like he is diving into the shallow end.Skydiver preps for the big jumpWhen he jumps, he is expected to reach the speed of sound - 690 mph (1,110 kph) - in less than 40 seconds. Like hitting the top of the water, he will begin to slow as he approaches the more dense air closer to Earth. But this will not be enough to stop him completely.If he goes too fast or spins out of control, he has a stabilization parachute that can be deployed to slow him down. His team hopes it's not needed. Instead, he plans to deploy his 270-square-foot (25-square-meter) main chute at an altitude of around 5,000 feet (1,524 meters).In order to deploy this chute successfully, he will have to slow to 172 mph (277 kph). He will have a reserve parachute that will open automatically if he loses consciousness at mach speeds.Even if everything goes as planned, it won't. Baumgartner still will free fall at a speed that would cause you and me to pass out, and no parachute is guaranteed to work higher than 25,000 feet (7,620 meters).It might not be the moon, but Kittinger free fell from 102,800 feet in 1960 - at the dawn of an infamous space race that captured the hearts of many. Baumgartner will attempt to break that record, a feat that boggles the mind. This is one of those monumental moments I will always remember, because there is no way I'd miss this.