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1、关于发电机励磁系统失控原理分析和采取的技术改造陈子馨(四会市威整电站，广东 肇庆 526232)2008年8月20日摘要：励磁系统是水电站发电机组的重要组成部分，原励磁装置在输电线路遭雷击跳闸时出现了一系列的励磁故障。通过对故障现象的仔细分析排查，进行了相应的技术改造，使励磁系统恢复正常，并消除了设备隐患，保证电厂安全生产。图1幅。关键词：励磁系统 技术改造 性能1、引言威整电站的励磁系统是由广州电器科学研究所生产的TKL11型可控硅励磁装置配置的，厂家声称：可控硅励磁装置具有良好的频率特性，它可以在发电机频率4555Hz变化范围内，机端电压变化小于0.5%符合国家标准。威整电站的发电机多次出
2、现当输电线路遭雷击跳闸，或系统甩负荷。在上述工况下，因电站结线方式，发电机仍需要发电带厂用电，不能灭磁停机。故出现：在35kV油开关跳闸后，发电机过速、随后发电机过压，至使由厂用电供电的大批厂内附属电器设备，照明灯管烧毁、家用电器设备（电视机、空调和电脑）损坏。2、引起过电压的原因分析2.1、甩负荷试验经过对甩负荷过电压过程励磁装置可控桥输出波形观察和分析，发现：在甩掉负荷的初始，因发电机没有负荷，励磁系统出现强减，可控硅首先出现全关，（由于大电感和续流管的续流作用，励磁电流并不等于零的，而是从原来运行中带负荷励磁电流值，迅速下降）由于励磁电流下降，又要维持机端电压的恒定，到电流下降到接近空载
3、励磁电流值时，可以看到可控硅的输出波形又重新打开，稳定在空载值附近。这段时间发电机没有过压，而是维持在额定电压上，在这段时间里属于正常调节作用；但随着往后发电机转速还不断升高，在转速超过约1.3倍额定转速时，即发现可控桥的输出波形由原来三相对称输出，突变成马鞍形的单相导通失控波形，随即励磁电流猛增，发电机电压升高，出现过压。从上述现象十分清楚：在发电机甩负荷初始产生过速期间（约1.2倍过速范围内）励磁系统调节正常的，它能实现强减，也不因为过速，一样可以使机端电压维持在额定水平上。问题是出现在当发电机转速超过1.3倍后，出现失控，励磁电流升高，才产生过电压。2.2、系统原理分析根据广科提供的励磁
4、系统图纸和原理说明，在励磁装置中的移相触发单元是采用与整流变压器电压相位对应三相同步信号作为同步电压、用控制电压作为移相信号，采用R、C移相，保证脉冲和移相范围均落在对应控制的该相可控硅正向阳极电压上，可控硅导通范围=15-120。励磁系统设计在，发电机空载运行时，可控硅导通角约65-70；发电机额定运行时，可控硅导通角约85-95。为了防止强减时移相把脉冲移到对应整相电压范围以外，形成掉脉冲，所以在“截止”也把最小导通角min设定在15左右。既然移相范围、最小导通角都把脉冲限制在=15左右，也就是说脉冲不会移出该相正半周范围以外，不会掉脉冲，不会出现失控。按理的确如此，但是，上述已提及，该励
5、磁系统的触发单元是采用R、C充电形式，固定R和C的值，利用改变充电电压的值（控制信号Ug）来改变充电时间常数，调节脉冲出现时间，达到移相的目的。系统选用R、C的值以及控制信号、截止控制电压（对应最小导通角）的设置，均是建立在每周期为20ms，也就是发电机在50Hz工况下设计的，（当然按标准要求也考虑到频率在10%变化内也能正常工作）。但是一旦超出允许工作范围情况就不一样了，事实上正是这样，当发电机频率超出1.3倍时，电压周期已经再不是20ms了，随着发电机从50Hz升速，周期就要逐渐缩短，因为原来的R、C数值不变、最小导通角限制电压值不变，也就是推到最后的脉冲位置不变，随着周期的缩短，脉冲位置
6、又不变，相对在每一周期内脉冲往后移，频率一再升高，周期再缩短，一旦脉冲移到对应该相电压正半周范围以外，就相当于掉脉冲了，一旦脉冲掉失，对半控整流桥大电感负载来说出现单相导通（即失控）是必然的了。（因为半控整流桥在电感负载下，每一相可控硅的关断是靠后一相可控硅触发导通，强迫前一相关断的，一旦脉冲掉失，后面一相可控硅得不到触发导通，前一相可控硅在电感作用下在负半周仍维持导通，持续到下一个周期正半周到来又继续导通，一直不能关闭，形成单相导通，这就是失控。）3、改造方法由上述分析得出结论：原励磁系统移相触发器的最小导通角限制，只能应用在50Hz10%范围内起作用，一旦频率偏移太多，将会使脉冲掉失。要实
7、现比较大范围内的最小导通角限制，必须采用锁相限制，我们的技术改造就是采用相位锁定进行的。见图1图1 锁相脉冲原理图在原有励磁系统里添加一个锁相脉冲单元，单元的组成部分是一个单相整流滤波电源和三组脉冲发生器组成（见原理图），插板的1、2脚接交流24V，该电源通过一个220V/24V的单相变压器由厂用电提供，此电源仅供本插板三组脉冲发生器之用；插板的4、9、17脚分别接入原励磁系统供小容量调试电源用的a相、b相和c相电源，6、8脚是A相锁定最后脉冲输出（最小导通角限制）；12、14脚是B相锁定最后脉冲输出；18、20脚是C相锁定最后脉冲输出。A、B、C三个锁定脉冲分别接A、B、C三相可控硅的触发极
8、，与原脉冲并连。它锁定最小导通角（min）的原理是这样的：首先，因为a、b、c三相小容量调试电源原设计就与整流桥三相A、B、C输入同相位，输入到脉冲锁相单元的同步电压Ua0、Ub0、Uc0为相电压，而输入硅整流桥的是UAB、UBC、UCA均为线电压，线电压比相电压迟后60。下面以A相为例，当4、10脚输入ao为正半周时BG1导通、BG2截止，到ao从正半周转入负半周的一刻，BG1随即关闭，在C2微分作用下BG2立即瞬时导通，通过脉冲变压器MB在6、8脚输出一个尖脉冲，由于C3作用使尖脉冲前沿更陡。这脉冲本来正好产生在=0的位置，但是因为UAB比Ua0迟后60，相当于这脉冲落在UAB整流线电压上
9、前移60，使min=60。为了使最小导通角再小一点，在BG1输入端的二极管两端并联一个0.47f的电容C1，由于C1和R1的移相作用，可以使ao相电压相位在C1两端迟后20-30左右，这样该脉冲就出现在min=30-40的位置上了，该脉冲并联在原移相脉冲（A相可控硅触发极）两端，它仅与相位有关，与控制信号Ug电压无关，并且一直出现在=30-40的位置上，在正常运行时，正常调节脉冲在min的前面，该锁定脉冲在其后，不影响正常调节；一旦甩负荷时，频率上升，调节器强减，调节脉冲往后移，当移至min以后，锁定脉冲就起作用，使最小导通角在频率上升也能锁定在30-40左右。B、C相同理也是如此。这样就再不
10、会掉脉冲和出现单相导通（失控）了。4、结束语新装这锁定脉冲插件后，经试验、多年运行，在雷击跳闸甩负荷情况下，发电机过速时，不会出现过压现象。证明这样改造是可行的，分析是正确的。 作者：陈子馨，男，助理工程师，副站长，从事电站技术管理广东省四会市威整电站 邮编526232 电话：0758-3788323 13602994902 电子邮件：Editors note: Judson Jones is a meteorologist, journalist and photographer. He has freelanced with CNN for four years, covering sev
11、ere 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 st
12、ep 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
13、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 s
14、et 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 待添加的隐藏文字内容2Watch man jump from 96,000 feet Tuesday, I sat at work glued to the live stream of th
15、e 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, b
16、ut 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
17、 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 c
18、ould 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
19、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
20、 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 c
21、an 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 E
22、arth 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 jum
23、ps, 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
24、, 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
25、 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 t
26、han 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.