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1、汽轮发电机轴电压试验浅析廖圣 陈辛（云南电力技术有限责任公司，昆明 650051）摘要：在一些特殊情况下，传统轴电压试验方法测量的轴电压值与真实值偏差较大，甚至会导致试验结论错误。因此,本文建议对传统的试验方法进行修正。 关键词：轴电压 试验方法 大轴 轴瓦0引言从预试规程轴电压试验项目的第一条、第二条要求来看,轴电压试验的试验目的是要检查轴瓦对地绝缘情况，同时检查轴电压大小。针对传统试验方法的不足,本文建议对传统试验方法进行修正。1轴电压产生的原因轴电压产生的原因主要有四种：、定子迭片接逢不对称、转子偏心等原因造成的磁路不对称，由此产生轴电压；、发电机出口发生单相接地事故、转子绕组匝间短路或
2、者两点接地、剩磁等原因产生轴向磁通，轴向磁通会在轴承与其附件之间产生单极电势； 、蒸汽与高速转动的叶片之间产生的静电荷，对轴与地之间的电容充电，引起轴电位升高，根据运行工况不同，升高的电位值不同，高时可达上百伏，此电压并非一直存在的，只在偶然的工况下产生；、静态励磁系统等在转子绕组上外加电压。根据励磁回路参数不同，可以产生几十伏甚至上百伏的轴电压。2传统的轴电压试验方法2.1传统试验方法依据规程提出：1）汽轮发电机的轴承油膜被短路时，转子两端轴上的电压一般应等于轴承与机座间的电压。2）汽轮发电机大轴对地电压一般小于10V。其目的，第一条是检查轴瓦对地绝缘情况，防止油膜承受全部轴电压，第二条是检
3、查轴电压大小。汽轮发电机大轴接地方式如图1图1 汽轮发电机大轴接地图2.2传统试验方法根据规程要求，试验前要提起汽端大轴接地铜刷，并将大轴两端油膜短接，测量大轴两端电压及大轴对地电压，测量方法如图2、图3图2传统轴电压测量图图3传统轴电压测量简化图由图3可以发现，因U1、U2测量的电压实际为同一电压，因此，U2必然等于或者接近U1。在绝缘垫和油管对地绝缘都良好时,传统轴电压试验可以准确测量轴电压值,并发现轴电压偏高的问题,但如果绝缘垫或者油管对地绝缘异常,而轴电压值小于10V时,会误下合格结论。3修正后的试验方法3.1 测量U1测量U1的目的是检查轴电压大小是否满足规程要求。现场可能出现因安装
4、方法错误或者安装工艺不良，导致励端轴瓦金属性接地，为了减小大轴内阻对轴电压的分压效果获得真实的轴电压值，应将汽端接地铜刷提起，两端油膜不进行短接。测量方式如图4。图4 U1的测量方法3.2测量U2测量U2的目的是检查励端轴瓦对地绝缘情况。当轴瓦对地绝缘正常时(即油管对地电阻正常,且两块绝缘垫至少有一块绝缘正常)， 0。当轴瓦对地绝缘异常时，U2U1，甚至U2=0。图5 U2的测量方法3.3 测量U3、U4测量U3检查上层绝缘垫绝缘情况,U4检查下层绝缘垫绝缘情况。图6 U3的测量方法当上层绝缘垫绝缘情况良好时，一般满足0，绝缘情况异常时，U3U1，甚至U3=0。同样，短接上层绝缘垫，测量下层绝
5、缘垫上的压降U4，可以判断下层绝缘垫的绝缘情况，这里就不进行复述了。3.4 加测U5如果在安装油管时未安装绝缘环，励端金属外壳、轴瓦会金属性接地，U2=U3=U40。当两块绝缘垫安装错误（固定螺栓将金属外壳、固定铁板及发电机机座连通）时，也会出现金属外壳、轴瓦金属性接地，也有U2=U3=U40。加测U5可以区分这两种情况，U5测量方法如图8。用短接线将发电机励端大轴电位引至两块绝缘垫之间的固定铁板上(参看图7)。如果轴瓦及金属外壳是通过绝缘垫的固定螺栓接地的，短接过程会产生很明显的放电现象，并且U5的测量值远小于U1；如果轴瓦及金属外壳是通过油管接地的，短接过程无放电现象，测出U5接近U1。图
6、7汽轮发电机励端大轴示意图图8 U5测量方法4轴电压测量实例4.1试验数据某电厂4台机组中,#1、#2、#3机因安装原因,导致发电机励端轴瓦及其外壳接地,#4机正常。这4台机采用传统试验方法测量的轴电压值见表1,采用新试验方法测量的轴电压值见表2。表1采用传统试验方法测量的轴电压值测量项目#1机#2机#3机#4机U1(V)3.73.23.44.6U2(V)3.73.23.44.6试验报告结论:试验数据满足规程要求,结论合格。表2 采用新试验方法测量的轴电压值测量项目#1机#2机#3机#4机U1(V)4.24.44.54.6U2(V)0-1波动0-1波动0-1波动4.4U3(V)0-1波动0-1
7、波动0-1波动4.4U4(V)0-1波动0-1波动0-1波动4.4U5(V)4.04.34.3/4.2数据分析4.2.1传统的试验方法测量的试验数据分析1）横向比较，#1机、#2机、#3机比#4机的U1小，纵向比较，#1机、#2机、#3机用传统试验方法测量的U1比新试验方法测量值小。因#1机、#2机、#3机励端轴瓦及其外壳经低阻（设为R1）接地，用传统试验方法时，大轴内阻r与R1进行分压（见图9，因绝缘垫电阻、油管对地电阻远大于R1，三者并联电阻接近R1，因此图中忽略了绝缘垫电阻和油管对地电阻的影响），导致U1测量值偏小（轴电压真实值为U1，U1=U1-Ur）；图9某电厂用传统试验方法测量轴电
8、压示意图2）因U1、U2实际为同一电压，所以U2=U1。（参看图3及2.2节分析过程）因此传统的试验方法，未能反应轴瓦对地绝缘情况，误下合格结论。4.2.2新试验方法测量的试验数据分析1）因新试验方法油膜参与分压，大轴内阻r相对油膜电阻来说很小，大轴内阻的分压效果可以忽略不计，因此，测量的U1值接近真实值；2）U2、U3、U4实际是轴瓦对地绝缘电阻与油膜电阻分压值，从表2试验数据来看，#1机、#2机、#3机轴瓦对地绝缘异常；3）因#4机测量的U1、U2、U3、U4均正常，所以不需要测量U5。#1机、#2机、#3机测量的U5与U1接近，说明绝缘垫绝缘情况良好，轴瓦是通过油管接地的。 试验结论：#
9、1机、#2机、#3机轴电压大小不超标，但轴瓦通过油管接地，结论不合格。#4机试验数据正常，结论合格。5结论新的试验方法通过比较绝缘垫与油膜的压降，比较绝缘垫与油膜的电阻值，可以判断励端轴瓦与地之间的绝缘情况。通过增加测量U3、U4电压，可以判断出每一块绝缘垫的绝缘情况。当励端轴瓦经低阻接地时，通过加测U5，可以区分轴瓦是经绝缘垫固定螺栓接地的，还是经油管接地的。新的试验可以准确测量轴电压值大小，全面、真实地反映轴瓦（包括绝缘垫、油管）对地绝缘情况，避免了对不合格试品误下合格结论的现象。参考文献：1 DL/T 596-1996.电力设备预防性试验规程S.2 GB 50150-2006.电气装置安
10、装工程 电气设备交接试验标准S.3 C.Ammann静止励磁的发电机中产生的轴电压问题和解决方法J.IEEE Transactions on Energy Conversion,1988.4 高志强，郝晓光.汽轮发电机轴电压分析及一例故障处理J.河北电力技术，2004，23（6）：16-18.5 李翔，韩浩，赵强.发电机大轴接地碳刷引起跳机事故的分析和处理J.东北电力技术，2005，26（6）：36-37.6 李建明，朱康，等.高压电气设备试验方法M.北京：中国电力出版社，2001. Editors note: Judson Jones is a meteorologist, journali
11、st 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 th
12、e worlds 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
13、 heartbroken. Yet the privatized space race has renewed my childhood dreams to reach for the stars.As a meteorologist, Ive still seen many important weather and space events, but right now, if you were sitting next to me, youd hear my foot tapping rapidly under my desk. Im anxious for the next one:
14、a space capsule hanging from a crane in the New Mexico desert.Its 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
15、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 cr
16、eated 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 d
17、id 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 claustr
18、ophobia 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 ab
19、orted.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
20、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 stratospher
21、e. 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
22、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, hell 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 divin
23、g 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 t
24、o 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 its 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
25、 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 wont. Baumgartner still will free fall at a speed that would cause you an
26、d 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 Id miss this.
