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1、磁性槽楔对大型永磁风力发电机性能的影响 何山1, 王维庆1*, 张新燕1，朱川江2 李建明3 (1.新疆大学北校区电气工程学院，乌鲁木齐市西北路134号 830008，2新疆金风科技股份有限公司，乌鲁木齐市上海北路107号 830026，3.新疆美克化工有限责任公司, 库尔勒市石化大道开发区 841001 )摘要：本文介绍了磁性槽楔的种类和特点，以及磁性槽楔在电机节能中的原理和实际作用。通过建立金风62型（1.2MW）永磁直驱同步风力发电机的电磁场模型，使用导磁性能不同的槽楔进行实际计算和测试。表明：发电机使用导磁性能较好的磁楔(相对磁导率310之间)，不论空载或负载，电机的气隙磁密分布都会较
2、不使用磁楔变得更加均匀；计算了磁密脉动减小的具体数值；得出了铁耗的具体数据；减小了气隙系数；降低了电机的温升；提高了效率。但同时应考虑到今后应尽可能地增大槽楔的电阻率，减少槽楔自身的损耗。为永磁风力发电机效率提高和设计优化提供计算依据。关键词：磁性槽楔；永磁直驱；气隙磁密；效率；风力发电中图分类号：TM 311 文献标识码：A1 引言电机节能是人们关注的重点，电机的效率即使提高1 %也能产生巨大的社会经济效益。永磁发电机作为清洁能源的源头，它的能量转化效率的提高是一个重要问题。随着风力发电事业的不断推进，风电占总能源的比重不断上升，磁性槽楔的应用和性能优化成为提高永磁直驱发电机效率的很好措施。
3、2磁性槽楔的分类、特点和现状磁性槽楔是在制造普通槽楔的材料中加入导磁材料，经过热压、固化形成。近年来，随着磁楔价格的降低和可靠性的提高，越来越多的用户使用磁楔1。磁楔分为：磁性槽泥、各向同性磁楔、各向异性磁楔。磁性槽泥槽楔由涂抹的槽泥量决定，人为因素较大，磁性能不稳定，节能效果和机械强度差，运行过程中易脱落；各向同性磁楔的力学性能有所提高，但磁楔的导磁作用使电机漏抗增加，降低了电机的起动转矩和最大转矩；各向异性磁楔中不但有磁性相、基体相和增强相，还有非导磁的补充相，补充相使磁楔在Y方向的磁导率大于X方向的磁导率，从而使磁楔的导磁性能出现各向异性2。各向异性磁楔一般采用模压法生产。电机可以在起动
4、转矩和最大转矩仅下降34 %的基础上，效率提高12 %。国外电机行业已经广泛使用磁楔取代绝缘槽楔，研制的磁楔在20kA/ m的外加场强下相对磁导率达8，抗弯模量达220MPa。国内磁楔与国外相比还有较大差距：主要表现在模压磁楔磁性能较高，而强度欠佳，下线时磁楔常被打碎或起层；层压磁楔力学性能较高，但磁性能却不理想3。3磁性槽楔对永磁发电机性能的影响金风62型永磁同步发电机，采用外转子结构，永磁体（磁钢）贴在转子轭上，由风机带动旋转，定子绕组位于内部（局部建模见图1），采用磁楔，PN =1.2MW，定子576槽，UN =690V，nN=20r/min，转子铁心外径Do=4600mm，转子铁心内直
5、径Di=4486mm。基金项目：国家自然科学基金项目（50767003）；新疆大学校院联合项目资助。图1 永磁发电机的结构简图 Fig.1 Structure of PMG 3. 1永磁发电机的铁损耗发电机空载所测量的电机铁损耗，叫空载铁损耗，它由基本铁损耗和附加损耗组成。基本铁耗主要是指磁钢产生的主磁通在定子铁芯齿中和定子轭中产生的磁滞和涡流损耗4。由于同步发电机正常运转时转子磁场转速和定子电枢磁场转速相同，故主磁通在转子内引起的铁耗忽略不计，基本铁耗主要产生在定子铁心中。附加损耗主要是指铁心表面损耗和齿中脉振损耗，它是由气隙中的谐波磁场引起的。这些谐波磁场由两种原因产生：一是铁心开槽导致气
6、隙磁导不均匀，齿槽效应在电机内引起的谐波磁通而在定子、转子铁芯中产生的；另一种是由于磁钢励磁建立磁场，磁密在空间的分布波形近似为一平顶波，根据傅立叶变换可知：空载励磁磁势在空间分布曲线中有较大的谐波存在。当谐波磁场相对定子磁极表面运动时，就会在极面感生涡流，产生涡流损耗；当谐波磁场相对于定子齿运动时，就会在齿中产生涡流及磁滞损耗，称为脉振损耗。表面损耗和脉振损耗是空载铁损耗中的主要损耗，占附加损耗的7090 %。3.2磁楔对发电机附加损耗的影响采用磁楔可减少表面损耗和脉振损耗。发电机定子的表面铁耗Ps1由下式表示5 （1）其中，k1：铁心表面的加工系数；Z1：定子齿数；n：电机转速；t1：定子
7、齿距；b：槽口宽度；B：气隙平均磁通密度；1：与b/比值相关的系数。楔入磁楔后电机k减小（见式2），表面损耗减小；磁楔封闭槽口相当于减小bs，引起1减小，也可降低表面损耗；磁楔的导磁作用使气隙磁场均匀，定子齿表面的磁密脉动减小6，这也能减少表面损耗。电机运行时，脉振损耗和定子齿内磁通密度脉动的幅值成正比关系。楔入磁楔后，由于磁楔的导磁作用，一部分磁通将通过磁楔到达定子，定子齿中的磁通密度分布趋于均匀，不会出现明显的脉振变化，从而使脉动幅值大幅下降，进而减小电机的脉振损耗。3.2.1空载气隙磁密目前金风62型发电机采用（相对磁导率）为3.0的磁楔，采用磁楔空载时的气隙磁密在一个磁极下（以图1中间
8、磁钢覆盖区域为例，以下同）的分布如图2，与使用常规绝缘槽楔（1）形成的空载气隙磁密（如图3）相比较，可见：气隙磁密的幅值由1.957T变为1.837T，磁密的最小值由1.11T变为1.303T。采用磁楔的气隙磁密的脉振幅值显著减少，电机表面损耗减小。另外由于有一部分磁通通过磁楔，所以齿中磁密降低，脉振损耗也会降低。 图23磁楔空载时的气隙磁密 图31非磁性楔空载时的气隙磁密Fig.2 Air-gap magnetic flux density Fig.3 Air-gap magnetic flux density when3 and empty-load when1 and empty-loa
9、d3.2.2负载气隙磁密发电机负载后，气隙磁场由磁钢磁场和电枢绕组磁场共同建立。由于发电机一般都带动电感电阻性负载，可知：电枢磁场会对磁钢产生去磁和交磁性质的电枢反应，气隙磁密波形会发生畸变（一个磁极覆盖的区域下，部分磁场加强，部分磁场减弱）7。在发电机额定负载运行时，绕组流过额定电流，电机采用磁楔（3）时的气隙磁密在一个磁极下的分布（图4），与使用常规绝缘槽楔（1）的负载气隙磁密（图5）相比较，可知：磁密最小值有所增加，磁密脉振减小明显，分布状况改善。 图43磁楔额定负载时的合成磁密 图51非磁楔额定负载时的合成磁密Fig.4 Air-gap magnetic flux density Fi
10、g.5 Air-gap magnetic flux density when3 and rated-load when1 and rated-load3.2.3采用高磁导率槽楔的气隙磁密随着槽楔性能的不断改善和提高，高磁导率的槽楔必将在电机的制造中得到广泛使用，目前使用的磁楔的磁导率还较低，将来如果使用9的高磁导率槽楔，气隙磁密分布如图6所示，电磁性能会更加优异。 图69磁楔空载时的气隙磁密 图7 楔入磁楔后的定子槽Fig.6 Air-gap magnetic flux density Fig.7 Slot of the stator with magnetic wedges applied
11、when9 and empty-load 3.3磁楔对电机温升的影响发电机定子槽口如果使用绝缘槽楔，气隙系数为8: （2）采用磁楔后（图7），气隙系数为： （3）其中，为气隙平均长度；t为齿距；b1为槽楔宽度；h为磁楔高度。令，y0，则 （4）又令， (5)0 ， 1 ，0，由上可知是变量y的增函数，0， 0，则也是变量y 的增函数。由于y 随着的增大而减小，因而楔入磁楔后电机的减小。电机的空载电流，所以的降低引起的降低。和的降低使定子和绕组的发热量减小，电机的温升减小；另一方面，金属磁粉的传导系数远大于绝缘材料，磁楔散热性能优于绝缘槽楔，散热容易，使电机温升下降9。3.4磁楔对电机效率的影响
12、采用铁磁材料制成的磁楔，由于导磁系数大，能增大定子齿部的有效截面积，降低磁阻和损耗，电机效率得以提高10。采用不同材料的磁楔，发电机带额定负载运行的铁耗可以利用两种方法计算:1.根据计算出的合成磁密数值大小,结合定子齿的重量,利用传统公式计算；2.利用有限元软件自带的后处理功能计算得到。采用有限元理论计算和实际测试结果见表1。表1 磁楔磁导率和发电机铁耗Tab.1 Magnetic conductance of wedge and iron-core waste 4结论(1) 采用磁楔后，发电机的气隙系数减小（相当于有效气隙缩短），可降低励磁电流，使空载电流下降。(2) 发电机槽口尺寸越大，使
13、用磁楔的节电效果明显。(3) 不论在空载和负载状态，磁楔磁导率加大，经过计算：磁密分布都会更加均匀，脉振幅值减小，磁密最小值增加，铁耗减小明显。因此希望磁楔大些。但是磁导率也不能过大，否则会引起磁楔的涡流损耗增加较多，磁楔加速老化，所以使用时应选择一个合适的值。国外磁楔的相对磁导率不大于1011，国内一般在5.0以内。由于制作中大量铁粉的加入和压力作用下部分铁粉的粘连，目前磁楔的电阻不高。磁楔的电阻率较低，导致磁楔中涡流损耗上升。制造使用高磁导率和高电阻率的磁楔，是进一步降低电机的损耗和温升的有效途径12。(4) 发电机损耗降低，效率提高；发热量下降，温升降低，可延长寿命13；(5) 由于磁楔
14、内部可流过部分磁通，使气隙中磁密分布趋于均匀，故可降低噪声和振动。 (6) 目前的槽楔的机械强度还不高，在电磁场分析计算的基础上，还可以计算磁楔的受力，进行强度校核；磁楔形状、材料和性能的进一步优化。通过以上分析，对于大功率、开口槽的风力发电机而言，采用磁楔对于气隙磁密分布会有较大改善，不失为提高效率的一项有效且简单的措施，是节约电能的一个好办法。参考文献：1伍庆体磁性槽楔的研究和应用J电机技术，2005.02：49-51.2李军 等.层压磁性槽楔的性能及其对电机性能的影响J.中国电机工程学报,Vol.25 No.16 Aug. 2005,126-131.3李军丽磁性槽楔在电机节能技术中的应用
15、J中小型电机，2005.32（2）：57-59.4胡新晚磁性槽泥在改善电动机性能中的应用J中小型电机，2004, 31 (1).5 Mikam H，Ide K，Arai KDynamic harmonic field analysis of a cagetype induction motor when magnetic slot wedges are appliedJIEEE Transaction on Energy Conversion，1997，12(4)：337-3436 Miyaji T，Tajima K，Sato TDecreasing of tooth pulsation lo
16、ss by use of ferrite wedges in a capacitor motorJJournal of the Magnetics Society of Japan，2003，27(9)：976-9817许实章.电机学 M. 北京： 机械工业出版社，1997，348364.8 马小芹，卢伟胜，张晓红，等电动机定子槽楔松动的声检测研究J中国电机工程学报，2002，22(2)：11-159 栾茹，傅德平，唐龙尧新型浸润式蒸发冷却电机定子三维温度场的研究J中国电机工程学报，2004，24(8)：205-20910 赵家礼电机节能技术问答磁性槽楔与磁性槽泥的应用M北京：水利电力出版社，
17、199411 aa，王绍禹，张国权等译磁性槽楔交流电机M北京：水利电力出版社，198712 李隆年电机设计M北京：清华大学出版社，199213 李伟力，侯云鹏，周封，等大型水轮发电机定子股线导热的数值分析J中国电机工程学报，2001，21(7)：115-119Magnetic Slot Wedge Effect of Performance to Large Direct-drive Permanent Magnet Generator (PMG) in Wind-power He Shan1 , Wang Wei-qing1*, Zhang Xin-yan1,Zhu Chuan-jiang2
18、 ,Li Jian-ming3 (1. College of Electrical Engineering,Xinjiang University,Urumqi 830008 ,Xinjiang ,China；2. Gold Wind Science Technology Co,LTD, Shang Hai North-road 107, Urumqi, 830026, Xinjiang, China;3. Petroleum-chemical industry road exploitation area, Korla 841001, Xinjiang, China )Abstract:Th
19、e article introduce magnetic slot wedge category and trait, as well as theory of economize on energy and effect in practice . By created Gold wind 62 (1.2MW) direct-drive permanent magnent synchronous generator electromagnetism field model ,through calculation and test,indicate,if use performance be
20、tter magnetic wedge（relatively magnetic conductance about 310） ,whenever empty-load or fully-load , magnetic flux density in air-gap will be uniformity， compare to commonly slot wedge,reduce pulsatile amplitude，minish iron-core waste,shrink air-gap coefficient,fall temperature,enhance efficiency. Co
21、nsidering to increase magnetic slot wedge resistance,decrease waste in wedge.It can be seen as basis to improve efficiency and optimize design about generator.Key Words: Magnetic slot wedge, Direct-drive permanent magnent synchronous generator，Air-gap magnetic flux density, Efficiency,Wind-power作者简介
22、：何山（1974），男，江苏金坛人，博士生，研究方向为洁净能源及其控制技术。通信地址：新疆大学北校区电气工程学院，830008，电子信箱：heshanxju TEL： 13579281309待添加的隐藏文字内容3王维庆（1959），男，通信作者，教授，博导，从事洁净能源的科研工作，电子信箱：wwq59。张新燕（1964），女，教授。Editors note: Judson Jones is a meteorologist, journalist and photographer. He has freelanced with CNN for four years, covering sever
23、e 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 worlds first satellite - Sputnik. I also missed watching Neil Armstrong step
24、 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
25、 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: a space capsule hanging from a crane in the New Mexico desert.Its like the set
26、 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 St
27、ratos 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
28、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 an
29、d 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
30、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
31、 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-d
32、ay 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 l
33、ot 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
34、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 diving into the shallow end.Skydiver preps for the big jumpWhen he jumps, he is exp
35、ected 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 st
36、abilization 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 order to deploy this chute successfully, he will have to slow to 172 mph (277
37、 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 and me to pass out, and no parachute is guaranteed to work higher than 25,000 fe
38、et (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.
