毕业论文设计新型灭磁在自并励发电机上应用研究29904

专业好文档 新型灭磁在自并励发电机上应用研究 陈贤明 王伟 吕宏水 刘国华 朱晓东 国电自动化研究院 电气控制研究所 南京323信箱 , 210003摘要：文献1讨论了非线性电阻和电容器并联后，跨接到磁场绕组两端的新型灭磁方案，主要是利用磁场开关主触点分断后，由电容器和磁场绕组产生谐振，导致电容器电压上升，当电容器电压上升到超过或等于非线性电阻残压时，非线性电阻即投入，电容器上电压不再上升，这种灭磁的方法，对灭磁开关的开断弧压要求降低了，本文进一步探讨自并励水轮发电机空载误强励下，用新方案灭磁的情况，这里利用了在d,q轴坐标下同步电机Park方程，考虑了阻尼绕组和发电机空载特性饱和的影响，进行了仿真，得到了予期的结果。关键词：水轮发电机，自并励，灭磁，电容器，非线性电阻An Application Study of a New De-Excitation Method for Generator with Self-Shunt Excitation Chen,Xianming Wang,Wei Lu,Hongshui Liu,Guohua Zhu Xiaodong ( Nanjing Automation Research Institute, P.O.Box 323 Nanjing 210003)Abstract: A new de-excitation method, in which capacitors with parallel connected varistorare connected to both terminals of field winding described in literature1. It utilizesresonance produced between capacitors and field winding, soon after field breaker opening.The resonance causes voltage rise of the capacitors . Varistor will put into operation when voltageof the capacitors rises higher than threshold value of the varistor Then voltage of the capacitors no long rises. Requirement for arc voltage of field breaker opening in this case is decreased.In the paper, with the new de-excitation method, de-excitation a self-shunt excited no-load generator after mal-forced excitation is studied. Park equations in d,q axis of synchronousgenerator with damping winding in rotor are used. Besides influence of saturation of no-load characteristic of generator is accounted. Finally an example simulation is implemented and the predicted results are obtained.Keywords: Hydraulic Generator, Self-shunt excitation, De-excitation, Capacitor, Varistor100.前言文献1探讨了用电容器并联于非线性电阻的传统灭磁电路进行了分析，其主要目的是为了降低对磁场开关开断弧压的要求，但并没有结合同步发电机的实际情况，本文将研究自并励水轮发电机空载误强励的情况下，新型灭磁方案灭磁的效果，为了尽量接近实际情况，考虑水轮发电机转子上阻尼绕组以及发电机空载特性饱和的影响，同步发电机的数学模型是按照d,q坐标轴下的park微分方程组建立。考虑到当前多数发电机组都采用维护方便，结构简单可靠，动态响应快的自并励励磁系统，因此本文也是有针对性地研究自并励水轮发电机在一种典型的严重故障情况，即空载误强励下的灭磁。本文利用Matlab/Simulink的软件，针对三峡左岸电厂的700Mw水轮发电机进行了上述情况的仿真。最后本文将研究新型灭磁方案下，对磁场开关开断弧压的要求，以及合理选择的原则，这也是本方案最终的目标。1.同步发电机park微分方程为了个简单起见，现在只列出同步发电机空载时在d,q轴坐标内的park微分方程.注意空载时定子电流的d,q轴分量id=iq=0 ,定子q轴磁链q=0 电压方程：定子： (1) (2)磁场： (3)阻尼绕组： (4)磁链方程：: 定子： (5)磁场： (6)阻尼绕组： (7)同时考虑发电机在同步速旋转，即P=2f，再将磁链方程代入电压方程后得 (8) (9) (10) (11)其中微分算子S=d/dt=p 按Simulink习惯书写。方程(8)至(11)便是水轮发电机空载的微分方程组。图1是自并励发电机的主线路，Tr是晶闸管整流桥，EPT是励磁变压器，它的起励和运行需要励磁调节器(AVR)进行闭环控制。 图1 发电机的自并励励磁系统 众所周知同步发电机空载特性是非线性的，应该指出,在经济和技术方面合理设计的水轮发电机，其在标幺制中的空载特性不应和下述常规空载特性 Uo=f(if) (标幺制) 相差太大。 表 1 常规空载特性 (前 2行)Uo0 0.551.01.211.331.4if0 0.51.01.52.02.5Uo0 0.551.01.1941.3221.4121 单位励磁电流if对应机端额定电压(Uo=1单位电压)为在仿真计算中便于计及空载特性的非线性，采用了文献2 推荐的表达式：如 if Ib 则 Uo=(M*if)/(N+if) , (13)其中Ib 是上述2个函数交点的励磁电流.如果实际的空载特性己知，就可用试凑法逐步确定合适的系数 L, M, N。对常规空载特性可采用以下值: L=1.1, M=1.95, N=0.95. 将它们代入(12),(13)中可得 Ib =0.823. 表1中的下2行为替代的空载特性 U0。 替代空载特性U0和常规空载特性U0 的误差很小，在工程应用中完全允许。对应于发电机空气隙主磁链的直轴互感Lad 当 if Ib =0.823 则 Lad =Uo / , 亦即, Lad =M/(N+)=1.95/ (0.95+) (15) 系数 是用来求 Lad的实际值，亨利2. 灭磁方程图 2 新型灭磁方案图2表示了作者们提出的新型灭磁方案1，本方案中用了磁场开关FMK的常闭触头，以防止发电机正常运行时，整流输出的磁场电压中负值谐波电压经电容器产生负向电流。二极管D是在利用LfCr谐振灭磁时，防止磁场绕组流过反向电流。初看起来灭磁时，在磁场开关断开瞬刻的发电机转子电路方程应为：Uf-Uk=rfif+S(Lfif+Ladi1d) (16)Uk为磁场开关开断弧压。但进一步分析可知：A).当磁场开关FMK常闭触头先合上、常开主触头未分开时，加于电容器C两端的励磁电压Uf为正，电容器电路因二极管D的单向性而不导通。B).当主触头分开时，产生了弧压Uk，如加于电容器C两端的Uf-Uk为负值时(注意开断弧压Uk必须大于Uf+U ,U是二极管D的管压降)，电容器电路接通，且电容器接通初瞬相当于短路，磁场电流if立即转移到沿着电容器C、二极管D的电路，使流过磁场开关常开主触头的电流迅速降至零，导致磁场绕组和励磁电源Uf断开，这时式(16)不再成立，而变成：rfif+S(Lfif+Ladi1d)+Ux=0 (17)和 ic+i1=if (18) 其中ic为电容器电流，i1为非线性电阻上的电流，它们可分别表示为：ic= (19) , i1= (20)注意因电容器C和非线性电阻R是并联的Uc=Ux。由于磁场开关FMK常开主触头断开到磁场绕组被电容器C短路时间十分短，因此上述方程(17)(20)就应是水轮发电机空载用本方案灭磁的基础。3. 仿真结构图图5 是自并励发电机空载或空载误强励灭磁仿真的Simulink总结构图，子模块SGmdl是包括灭磁方程(17)(20)在内的同步发电机空载下在d,q轴下方程(8)（11) 的数学模型，子模块PID是自并励发电机调节器（AVR）的核心，它的输入有电压给定Ref，和反馈量In1,即端电压U0 (额定相电压=11547v)的测量值的标幺值。开关Switch2及定时器Timer用于控制空载误强励的瞬刻，这里误强励假定因端电压测量值出错，降至0.9额定值引发，PID输出是用于三相全控整流桥晶闸管的触发控制角，它经Cos取值后，和来自端电压U0及励磁变压器变比及有关整流系数相乘后，得到了自并励系统的励磁电压，后者经开关Switch4送到开关Switch1去进入磁场绕组，Uf0=5v是自并励系统的点火电压。定时器Timer1 是用来控制灭磁瞬刻的，Switch4开关可用来控制灭磁瞬刻磁场绕组和励磁电源断开后，加上的零电压。 图5 自并励发电机空载误强励灭磁仿真用Simulink 总结构图图6是图5中”SGmdl”子模块的d,q坐标下空载同步发电机及灭磁模型。上部”de-ex”子模块是灭磁模块，其结构图如图7所示。其上部为求ic和i1的方程(18)，(19)，(20)，下部为计算灭磁后非线性电阻，磁场绕组，d轴阻尼绕组和电容器吸收的磁能,W,Wr,Wdp,Wc。开关SW是在非线性电阻的电流i1=0时，将电容器电压Uc切到零值，clk是灭磁起动信号。图6下部带分积分器1/S的电路代表方程（11）,上部带分积分器1/S的电路代表方程(10)，右下部为方程(8)，和(9).其中方程(8)中的微分算子S=du/dt在这用差分代替，以免状态突变时无解。模块Inductance1用来考虑受发电机空载特性饱和影响的d轴电感的参数，其中计及了式（14）,（15）注意这里对饱和起作用的除了if外，还有i1d。4.仿真结果 现以ABB公司为三峡左岸水电厂提供的水轮发电机数据为例，其主要数据如下：额定功率 700Mw图6.空载同步发电机在d,q轴和灭磁模型SGmdl图7 “de-ex”灭磁子模块额定电压 20kv (相电压11547V) 额定转速 75转/分 额定功率因数 0.9 额定励磁电压、电流475.9V 、4158A 空载额定电压下励磁电压，电流 191.8V、2352A，采用静止自并励系统。 (不饱和值/饱和值) 和 本仿真中转子磁场绕组电阻采用空载时的和130C的平均值即：rfd=(191.8/2352+0.1144)/2=0.098空载励磁电压用计算值 Uf0=2352*0.098=230.5v磁场绕组自感计算Lf=0.098*10.1=0.99H 假设磁场绕组漏感 Lfs 3 Lfs =0.187H 在本例中，假定ABB的水轮发电机空载特性为常规特性，用替代特性，即表1中第2，3行表示，此空载特性的转折点为Uo=0.905, if=0.823仿真中用到的发电机其它参数可参考文献3。在本例中假定非线性电阻是氧化锌=0.046, 额定励磁电流下灭磁时反压为2Kv其非线性系数k=1363。另外假定电容器C取1000微法。图5中各数字表表示了自并励发电机空载起励到额定电压的仿真结果，用来检验所给发电机参数的正确性，表1列出了发电机空载的实际给定值与仿真结果值，可看出两者十分接近。 表1结果对比端电压U0 (V)励磁电压Uf0 (V)磁场电流if0 (A)实际值11547230.52352仿真结果11550229.92348图8为自并励发电机空载额定电压下，在t=36”时发生误强励、t1=37”时灭磁，并假定磁场开关开断弧压满足灭磁新方案要求下，用新灭磁方案灭磁的仿真结果。图8E是励磁电压Uf、磁场电流if和电容器电流ic的变化过程，Uf在自并励起励至13”曾强励至600多伏，后稳定到230.1V，在误强励下增至1802V，灭磁开始，因灭磁开关分断而降为零。If起励稳定后达2345A，误强励下猛升到4845A，灭磁后迅速降至零，电容器电流ic仅在灭磁瞬刻由0突升到4836A，很快因转移至ZnO上而降至零，呈杆状。图8A是非线性电阻的电流i1和电压Ux，i1最大达4842A,Ux最大达2014V，灭磁时间为1.617”图8D为d轴阻尼绕组电流在起励强励阶段有约-60A. 稳定后为0，误强励发生时达-125A，而灭磁开始后升至+191.1A，随后减幅振荡至零，图8C 8F是定子端电压q轴,d轴分量Uq,Ud(因Ud比Uq可忽略，所示端电压U0=Uq)起励稳定后U0=11540V，误强励时猛升至15627V，灭磁后迅速 (A) (B) (C) (D) (E) (F)图8 . 自并励700Mw水轮发电机空载误强励，用新方案灭磁仿真的结果降至零，至零前的振荡是因i1d在if=0后，仍有振荡形成，Ud的量十分小，它的产生明显是由i1d感应产生。图8灭磁过程中各单元的吸能，ZnO是W=4.9175, 磁场绕组Wr=0.654,d轴阻尼绕组Wdp=0.462，电容器Wc=0 兆焦耳。5. 结论1. 从上述仿真结果看，在利用电容器电容和磁场绕组电感共振时电容器电压上升至非线性电阻残压，导致非线性电阻投入灭磁的新方案，是可能的，此时对直流侧磁场开关的开断弧压要求，已降低至稍大於最大磁场电压即可。2. 在本例中电容器C取1000微法，由于这种电容器工作方式，是单次脉冲式的，因此可选用直流冲击电容器，经查找北京电力电容器厂生产的一种直流冲击电容器规格如下：电压 2Kvdc,555F，重45kg，尺寸为663130475 只需两台。如电容量取得更小一些，电容的脉冲电流ic会更窄，是否会影响向非线性电阻移能，宜进一步研究。3. 文献1和本文说明及新灭磁方案的原理和仿真结果，欢迎同行们提出意见，下一步宜进行实地试验，希望最终能降低大型发电机磁场开关的尺寸和成本。参考文献1)陈贤明等“水轮发电机新型灭磁方案”(第三届电工技术前沿学术论坛录用，待发表)2)B.A.托尔文斯基”同步发电机通用空载特性及其分析表达式”前苏联1945No.2-3 第45-54页,列宁格勒 前苏联国家动力出版社3). 陈贤明，朱晓东，王伟等 “水轮发电机突然三相短路后灭磁研究” 2006 No.3第3845页作者简介 陈贤明 1958年哈尔滨工业大学电机系毕业，教授级高级工程师，从事电力电子技术在电力系统中的应用和发电机励磁的研究Editors 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 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 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: 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 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, 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 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 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 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 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.