毕业论文（设计）淮北发电厂5 号机励磁回路的技术改造.doc

淮北发电厂5号机励磁回路的技术改造王景军摘要：传统的励磁回路采用线性电阻灭磁，间隙保护作为转子过电压保护，这种励磁接线具有很多缺点。目前，系统内已有许多机组采用高性能氧化锌电阻作为转子灭磁电阻和过电压保护，具有良好的实用效果。介绍了淮北发电厂5号机励磁回路技术改造情况和高能ZnO电阻的原理及其在励磁回路中的应用。 关键词：励磁； 回路； 改造 1改造前的情况淮北电厂5号机为200MW机组，发电机型号为QFSN-200-2,额定转子电流1749A，额定转子电压453V，东方电机厂生产，西南设计院设计，投产于1981年12月，励磁方式为传统的三机交流励磁方式，励磁回路接线如图1所示。图1改造前的励磁回路接线图励磁回路接线及设备存在以下问题： a.原灭磁开关为早期DM2-2500/60型。一方面，这种灭磁开关动作很不可靠，运行中极易出现合不上、拉不掉等现象。特别是在事故情况下，如灭磁开关不能可靠跳闸灭磁将对发电机造成很大的损害；另一方面，这种灭磁开关结构复杂，不易调整，运行一定年限后难以保证技术性能。而且，这种灭磁开关小电流灭弧能力差，在转子电流小于600A时不能可靠灭弧。b.励磁回路采用线性电阻灭磁， 在转子磁场能量很大时， 转子易出现高电压； 转子过电压保护采用间隙保护，间隙保护定值难以整定，易变化；容量小，过电压保护效果差，而且间隙保护易损坏，损坏后不易发现， 极易出现转子无过电压保护情况。 c.转子过电压保护仅是对发电机转子的保护，在灭磁开关跳闸后对励磁回路电源侧即硅整流回路没有保护。2改造后的情况淮北电厂5号机在近期大修中进行了增容改造，容量由原来的20万kW增至22万kW，改造后的发电机额定转子电流1845A，额定转子电压453V。与此同时，5号机灭磁开关及励磁回路也作了相应的改造。改造后的励磁回路接线如图2所示。这种回路接线与原回路接线从设备配置到原理接线都有很大变化。图2改造后的励磁回路接线图a.用上海立新电器厂生产的DM4-2500/2型灭磁开关代替原DM2-2500/60型灭磁开关。随着技术的不断进步，原DM2型开关已被淘汰，新型灭磁开关已大量应用于电力生产，DM4型灭磁开关即是其中较好的一种，据我们了解目前系统内已有很多电厂使用了这种新型灭磁开关。从1991年开始，淮北电厂14号机灭磁开关也先后更换为这种灭磁开关。4台灭磁开关更换后至今，运行状况良好。这种灭磁开关具有以下优点：结构紧凑合理、体积小、重量轻、制造工艺优良、运行稳定、便于检修维护；采用双断口灭弧，灭弧能力强，主触头烧损小；开关合闸采用双合闸线圈，合闸力矩大，分、合闸动作可靠；克服了原灭磁开关小电流灭弧能力差，在转子电流<600A时不能可靠灭弧的不足。b.用高能非线性ZnO电阻(FR1)代替原线性电阻。正常运行时，由于FR1回路串有反相二极管，回路没有电流通过。灭磁开关跳闸时，励磁线圈产生的反向电势将通过二极管和FR1回路，将励磁能量消耗在FR1上，从而使发电机迅速灭磁。由于FR1有良好的非线性特性，因此在发电机灭磁时，发电机转子电压被牢牢的限制在安全范围内，有效地保护了发电机励磁线圈的安全。c.增加了励磁回路电源侧过电压保护(FR3)。由于FR3接在励磁回路电源侧，在灭磁开关跳闸时，因电源侧线路电感贮存的能量将消耗在FR3上，从而达到保护励磁回路电源侧设备免受过电压损害的目的，克服了原回路励磁回路电源侧没有保护的弊端。d.用高能非线性ZnO电阻(FR2)代替原间隙过电压保护，正常运行时，FR2，FR3均接入回路运行，共同起到励磁回路过电压保护作用。由于励磁电压一般在500V以下，FR2，FR3在正常运行时仅有很小的漏电流，并不影响机组的正常运行。当外来高压侵入励磁回路时，由于FR2，FR3良好的非线性特性，发电机转子电压也被牢牢的限制在安全范围内，起到了发电机转子过电压保护的作用。3转子过电压保护的原理转子灭磁电阻(FR1)及转子过电压保护(FR2，FR3)的工作原理都是基于高能ZnO电阻良好的非线性特性。ZnO电阻的伏-安特性如图3所示。图3ZnO电阻的伏-安特性根据新的励磁回路接线，我们可以看到在正常运行时FR2，FR3均接入回路运行。任何情况下有外来高压侵入励磁回路时，FR2，FR3中通过的电流将随励磁回路两端的电压升高而增大，电流大到FR2，FR3的拐点电压时，由于高能ZnO电阻的这种非线性特性使得其两端电压不再升高，将励磁回路两端电压限制在一定电压范围内，外来侵入高压消失后，励磁回路恢复正常运行；同理，在发电机转子灭磁时，FR1也将励磁回路两端电压限制在一定电压范围内，并且将强大的发电机转子内的磁场能量通过FR1消耗掉。4主要技术参数及现场试验情况转子灭磁电阻(FR1)及转子过电压保护(FR2)的技术参数应由发电机的容量和技术参数来决定，主要应满足以下两个方面的要求： a. 高能ZnO电阻的最大电压一般应为励磁额定电压的35倍，电压太低易造成发电机失磁；但电压也不宜太高，最高不得高于励磁绝缘耐压的65%，电压过高易导致发电机转子绝缘损坏。根据规程规定淮北电厂5号机转子耐压标准为4530 V，因此高能ZnO电阻的最大电压应选择为<3 000 V。高能ZnO电阻在60A时电压基本上不再升高，因此一般以该电压作为高能ZnO电阻的最大电压。5号机FR1与FR2的最大电压U60A分别为1200V和1400 V。 b.高能ZnO电阻FR1应有足够的能量裕度，以保证发电机转子不会因为部分ZnO阀片损坏而致绝缘损坏。为防止ZnO阀片击穿或损坏时造成发电机励磁回路短路，影响机组运行，每一ZnO支路均串有一只快熔保险。在ZnO阀片损坏短路时，该保险迅速熔断，使该支路退出运行；在发电机事故灭磁及出现转子过电压时，该保险也可能熔断。如高能ZnO电阻FR1没有足够的能量裕度，且上述保险损坏没有及时发现，则不能保证可靠灭磁。实践中这种高能ZnO电阻的能量裕度选择很大，即使在不超过二分之一退出运行的情况下仍不会影响装置的正常运行。其它技术参数：高能非线性ZnO电阻FR3的最大电压U60A选为1.5×U60A(FR1),实际配片电压为1800V；各元件的漏电流是指1/2U0.01A下的电流，应小于50A，各元件的实测最大漏电流为3A(FR1)，5 A(FR2)，7A(FR3)；阀片的残压比K=U60A/U0.01A,其值应在1.31.5之间。为检查该装置的实际灭磁效果，我们进行了发电机灭磁情况下的转子电压录波试验，录波示意图如图4。试验时，为防止高能ZnO灭磁电阻非线性特性不好，在发电机灭磁时电压过高，损坏转子，决定在空载额定电压下做灭磁录波试验，当时励磁电流为650A，励磁电压为110V。从录波图我们可以看到：在拉开灭磁开关后发电机励磁电压为反向电压，灭磁后0.05s电压最大约1320V，此后转子两端电压迅速衰减，约0.46s时衰减至额定电压，1s时衰减至330V。因此，这种灭磁方式有效地将转子电压限制在安全范围内，且灭磁速度很快。图4发电机灭磁情况下的转子电压录波示意图5存在问题a.淮北发电厂5号发电机的灭磁电阻是由20个支路ZnO电阻并联而成，每一支路均串有一只快熔保险。如上所述，快熔保险对防止ZnO电阻损坏而致励磁回路短路，保证机组正常运行是很重要的，但是这种快熔保险熔断时，仅由该保险本身发熔断信号，没有中央信号，运行人员不易及时发现。因此要求，一方面运行人员加强巡视检查；另一方面，在每一次灭磁电阻(FR1)事故灭磁后，对上述保险应进行检查，以便及时发现及时更换。b.这种灭磁方式及励磁接线方式虽然已在系统内大量使用，但有关技术规程和试验规程却相对滞后，给大量推广应用和现场维护检验工作带来很多不便，建议有关生产厂家及相关部门对此引起注意，及时进行有关技术鉴定、规程完善等工作。作者单位：王景军（淮北发电厂，安微淮北235002）参考文献：1王维俭.电气主设备继电保护原理和应用M.北京：中国电力出版社，19962屠黎明，吴济安，胡敏强.发电机内部相间短路纵差保护的灵敏度分析J.电力自动化设备，1999，19(1)：133曹险峰.微机发变组保护整定计算中的几点体会J.电力自动化设备，1999，19(5)：59604合肥凯立电子有限责任公司编.大型发电机组转子过电压及其保护ZEditor'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.