毕业论文（设计）异步电动机改作发电机运行的探讨

专业好文档异步电动机改作发电机运行的探讨韩 莉（平顶山工业职业技术学院自动化系，河南 平顶山 467001）摘要：文中依据电动机的运行特性，对异步电动机改为发电机运行的过程进行了分析和探讨，提出了异步电动机作发电机运行时必须注意的问题，并通过了实验室的试运行。关键词：异步电动机；电容器；感应电势1 引言三相异步电动机的定子绕组中流过三相交流电流可以产生一个旋转磁场，磁场切割转子导体在其中产生感应电流，于是转子导体在磁场中受到电磁力的作用，产生一个使转予转动的力矩。转子的转速n低于旋转磁场的转速n1=60f/p，它们之间有一个转差率s（） ，电动机的工作范围0s1。如果有一台原动机带动感应电动机，使其转速n高于旋转磁场转速，转差率的值小于零，此时旋转磁场也切割转子导体，只是其相对关系与电动机工作状态相反，此时的电磁力矩是制动性质的，原动机必须克服这个制动力矩才能使转子旋转，在这个过程中原动机做了功，它提供电动机轴上的机械能变为定子绕组输向电网的电能，这时的感应电动机工作在发电机状态，其有功功率从原动机来，它的无功功率(本身劢磁功率，定子转子漏磁)是从电网中吸取的，其值可达电动机本身容量的2025，这部分无功功率需要由电网供给，异步电动机作为发电机运行在电力系统中很少用。在煤矿提升机中，深井和斜井下放重物时，为了充分利用机械能，在等速运行阶段常采用这种运行方式。2 异步电动机改作发电机运行的实施过程M图 1电容器接线C由于异步电动机具有廉价，结构简单、维护方便等优点，对于野外作业用电，可考虑利用风力、水利、沼气等自然资源作为输入能量，通过原动机使其工作在发电状态还是具有采用价值的。当单机运行时无功功率的供应需借助于电容器提供。其接线见图l。2.1电压的建立过程首先异步电动机转子上必须有剩磁。当原动机带动转子旋转时，转子的磁力线就切割定子绕组，在定绕组中产生感应电势。由于电容器并在异步电动机的接线端子上，在的作用下，异步电动机和电容器间就流过。在忽略导线电阻的情况下，超前，与产生磁通的励磁电流的相位是一致的，它相当于励磁电流，相量图如图2所示。在作用下，异步电动机里的磁场增强，使感应电势增大，的增大又使增加，但它们的增加都有一定的规律，即与的关系要符合铁心的磁化曲线规律，同时Ic和V(=E)的关系又要符合欧姆定律即成线性关系，如图3所示。从图上看El作用于电容上，根据Vc=IcXc得Ic1，而在Ic1所产生磁场激励下产生感应电势E2，E2从磁化曲线E2=f(Ic)得到。在E2作作用下又产生电流Ic2，Ic2又产生E3，如此下去电动机的端电压逐渐升高，最后稳定在两曲线的交点E1E2E3E4BIc1Ic2Ic3Ic图 3 电压建立过程EB上，B点就是额定工作点。稳定输出电压的大小取决于电容器的值和原动机的转速。ENENIcIoa图2 相量图E12.2电容器容量的计算 为了保证异步电动机工作在发电机状态的输出电压频率f50Hz,所以异步电动机的转速应约等于异步电动机的同步转速，而电压建立的数值条件就是要有足够的电容量。电容量的选择很重要，电容量小了，电压建立不起来或不稳；电容量大了，所产生的电压高于额定电压。电容的接法分接和Y接。 如果接法，则 C （F）如果Y接法，则 C（F） 式中：VN为异步电动机的额定电压。Ioa为电动机的空载电流的无功分量，它可通过空载实验求出。由电动机空载实验读出功率Po和空载电流Io，求出空载功率因数:COSf0则 Sinf0 IoaIoSinf0 接法电容耐压值必须大于 Y接法电容耐压必须大于2.3输出功率计算这台实验电动机的IN =4.95(A)，Io=2(A)，如果负荷全部为电阻性负载，则 Ir=4.53(A)，输出功率P=VIr=3804.53=2978(W)。如果带电感性负载，输出功率会更多。我们在实验室采用一台功率为1.5KW的直流电动机拖动一台2.2KW的4极、VN=380V的异步电动机，电容接法，调整直流电动机的输入电压使异步电动机转速达到1500转分，通过计算C=9.6F,我们选择10F，通过两个20F耐压630V的电容串联，当空载电压达到400伏时，带上灯箱，随着负荷的增加，电压降低较多，重新调整直流电压，即重新调整原动机的转速使其保持1500转分，异步电动机的输出电压基本保持380V。如果用一台柴油机带动则转速基本恒定，电压也基本恒定。实验时我们把电容器由10F增大到20F (即单个电容单个运行) ，保持n=1500转分，电压急骤增加，达到450V,把个电容器击穿了这说明电容的选择很重要。3结语利用电动机的工作特性，可使其工作在发电机状态，向外输出电能。并对此成功进行了实验室运行实验。对不便直接获取电能的场所具有可行的实际意义。在异步电动机作发电机运行时必须注意以下几点：（l）电压建立时，电机必须空载，待电压建立后才可以加上负载。 （2）根据电压的大小随时调整转速。以免负载轻时电压过高，损坏电器设备。（3）如果异步电动机机带感性负载(如电机)，必须注意起动方式，以免因起动电流过大而颠覆整个系统。另外，在选择电容器时要充分考虑对耐压值的要求，留有足够的裕量。联系方式： 13017560710，E-mail：hanlipzxy地 址： 河南省平顶山市水库路3号院 邮 编：467001Editors 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.5