毕业论文（设计）研究水电站发电机励磁系统的应用.doc

研究水电站发电机励磁系统的应用于建伟中国水利水电第三工程局有限公司制作安装分局 陕西725005摘要: 近年来，随着现代科学技术的发展以及电站设备自动化水平的提高，电厂要求实现无人值班或少人值班，提高电厂发电工作效率，减少维护工作量，提高系统的可靠性和稳定性。励磁控制系统正是实现这些要求的关键设备。在水电站工程中，励磁系统更是整个电站的重要组成部分，它对电力系统及发电机本身的安全稳定运行有很大的影响。本文从对励磁系统的发展现状与趋势的分析入手，从结构及原理方面具体论述了水电站发电机励磁系统的应用。关键词：水电站、发电机励磁系统、应用中图分类号：TM6 文献标识码：A 文章编号： 水电站发电机励磁系统作为水电站中水轮发电机的一个重要组成部分，它承担着向发电机转子提供励磁电流的重要功能，因此励磁系统的性能好坏直接影响整个水电站的运行状况。随着电力系统的发展，对电力系统运行稳定性和机组运行可靠性提出了更高要求，迫切需要性能优、功能多和可靠性高的励磁系统，以满足电力系统稳定及综合自动化的要求。同时，近年来计算机监控技术在水电站中得到了广泛的应用，使得微机励磁装置也迅速在水电站中得到了推广。1、励磁系统的发展现状与趋势 从制造厂家来看，首先是有多家外国制造商，如广州抽水蓄能电站引进阿尔斯通的励磁装置，隔河岩电站引进加拿大通用电气公司的励磁装置，马迹塘、五强溪电站引进奥地利依林公司励磁装置，三峡水电站采用西门子的励磁装置等；也有引进技术的合作生产企业，如李家峡电站部分机组由东方电机厂与ABB合作完成；还有拥有自主知识产权的国有和民营科技企业，如国家电网公司南京自动化研究院、国家电力公司电力科学院、河北工业大学电工厂、华中理工大学等十多家单位都开发了数字式调节器。从水电站励磁装置的技术状况来分析，具有以下基本特点：(1)随着微电子技术、计算机技术、电力电子器件的进步，数字化技术不同程度地应用于各类励磁装置中。采用数字化励磁装置已经成为各类老机组技术改造和新机组设计选型的一种趋势。(2)水电站自动化系统的应用，无人值班、少人值守逐渐成为水电站运行管理的基本模式，水电站运行计算机监控系统、水电站经济运行计算机管理系统以及电网稳定运行计算机自动化调度系统都对励磁装置提出了新的要求。(3)励磁机采用静止励磁方式已经成为主流。许多相关技术如干式励磁变压器、非线性电阻、热管散热技术等被大量采用。(4)大型水电机组因可靠性、控制特性的高标准而要求励磁装置的进步明显加快，采用的都是高端产品。该类产品选择上侧重于性能和可靠性，对产品价格不做重点考虑。(5)抽水蓄能电站对励磁有其特殊要求，目前100000kw以上机组其成套设备包括励磁系统在内，主要引进外国产品。从励磁技术看，国内有实力的厂家也能制造，主要是缺乏经验和机会。(6)中小型水电站包括微型水电站其总量占绝大多数，从现在的市场情况看，这一领域主要是国产励磁装置的天下。老机组改造任务与新建项目各占一半。这部分产品要求的特点是具备基本功能、运行可靠、调试容易、价格低廉、维护方便。 因此，结合国内水电机组励磁调节装置研究开发情况及国外励磁技术的发展情况看，励磁装置开发的重点是调节器，例如设计了双微机励磁调节器等。双微机励磁调节器的双通道完全相同，无主从之分，可双向切换。从理论上讲，双通道同时出故障的概率很小，但在工程上因为双微机励磁调节器故障而引起机组被迫停机的事故也常有发生，其主要原因是切换不可靠。双微机励磁调节器目前已经是一种比较成熟的方案，主要用于大中型发电机。由于采用双微机励磁调节器会提高励磁系统的投入成本，考虑到励磁调节器在中小型发电机中所占的费用及在电网中承担的任务，要求励磁调节器在设计上简单、可靠、性价比高。因此，工程上把提高单微机励磁调节器的可靠性视为提高中小型发电机励磁调节器整体可靠性的最重要措施。2、微机励磁调节器的结构原理及应用分析 励磁调节器是发电机中极其重要的一部分。性能优的励磁控制器可以保证同步发电机运行的可靠性与稳定性。在正常运行时，励磁调节器供给发电机励磁电流，并根据发电机负载的变化作相应调整，以维持发电机机端电压或电网中某一点电压在给定水平上。当发电机突然甩负荷时，它实行强行减磁以限制机端电压，使其不会过度升高。此外，当几台发电机并列运行时，通过励磁控制器的作用可使无功功率在机组间得到稳定和合理的分配。为了实现上述功能，微机励磁调节器必须具备以下相应的硬件结构和软件设置。一般微机励磁调节器的工作原理如下图所示。微机励磁调节器的工作原理图2.1、信号测量部分 由上图可知，从发电机机端电压互感器YH和定子电流互感器LH来的信号调差后，经过数据采集和数据处理，转换成05V的直流信号输入到测量部分。对于电量的采集有直流算法和交流算法。直流算法所用的硬件较多，但简单；交流算法所用的硬件较少，但是程序的编写较为复杂。2.2、调差单元 为了使并联运行的各发电机组按其容量向电网提供无功功率，以实现无功功率在各机组间稳定、合理地分配，在自动励磁调节器的测量比较中设置了调差电路，用以改变发电机无功调节特性的斜率。若调差系数小，当无功电流变化时发电机电压变化就小。所以调差系数的大小又表征了励磁控制系统维持发电机电压水平的能力。2.3、调节控制部分 同步发电机的整个工作过程，可划分为两个阶段。第一个阶段，是指发电机从起励建压到并网之前，这一阶段的时间极短；第二阶段，是指同步发电机并网之后。此时励磁控制系统是通过调节励磁电流来调整发电机向电网输出的无功功率。这一阶段是同步发电机的主要工作阶段。励磁控制系统是一个典型的闭环系统。在控制系统中，往往通过系统校正，即在原系统中增加校正装置，改变系统的整体结构，从而使系统实现所需的性能。励磁控制系统的控制规律最终都归结为PID运算，PID运算仍然是基础。除了PID运算外，还有较为复杂的算法，例如模糊控制、人工智能等。需要说明的是算法上二的先进不代表这种算法能使控制对象的性能达到最优。它们的先进性更多的是体现在对不同控制对象的适应性方面，即鲁棒性。2.4、软件限制部分 为了同步发电机的安全、可靠、稳定运行，保护机组设备，要求励磁系统对各种极限运行工况作出反应，为此，在励磁调节器中附加了一系列励磁限制器，这里称之为软件限制部分。软件限制部分主要包括最大励磁电流瞬时限制器、反时限过励磁电流限制器、欠励限制器以及伏赫限制器等。2.5、移相触发及脉冲放大部分 励磁调节器中，移相触发及脉冲放大部分的任务是产生相位可调的脉冲，用来触发整流桥中的晶闸管，使其控制角随综合放大环节输出的控制电压的大小而改变，从而达到自动调节发电机励磁电流的目的。因此，该部分是调节器的关键部分之一，它要求：严格与励磁电源的电压保持相位上的同步；移相分辨率要高，移相范围要大；各相触发脉冲的控制角要一致，即对称性要好；能适用于单相半控桥、单相全控桥、三相半控桥或三相全控桥式整流电路；要具有频率自适应性能，即电网频率变化时，触发脉冲仍保持严格对称；产生的脉冲要有足够的功率，前沿要陡，要有适当的宽度。3、结语 水电站工程中，励磁系统是整个电站的重要组成部分，它对电力系统及发电机本身的安全稳定运行有很大的影响。因而，在工作实践中，不断加强对站内电机励磁系统的应用研究，对全网无功功率分布及有功功率损耗的管理和控制均有非常重要的意义。参考文献：1徐森，水电站发电机励磁系统.浙江科学技术出版社,2007.01.2张清茹，励磁控制与电力系统稳定，水利电力出版社，2008.07.3孙强，电力系统非线性控制，科学出版社，2008.10.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.