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1、专业好文档 基于声发射高压放电检测的探讨 刘永军 贡德忠河北省石家庄行唐县供电局摘要：本文介绍了近年来声发射技术在高压放电检测方面的发展及应用情况，探讨了高压放电检测原理、信号的提取以及干扰问题的解决,并对信号进行了频谱分析。并能够准确无误的判定高压放电现象,最后阐述了该理论的优缺点以及在高压放电方面的应用。关键字：高压放电 声发射 信号 检测0前言近年来，用户用电负荷越来越大，相关电气设备日渐增多，许多用电大户拥有自己的220kV变电所，并且对供电可靠性越来越高，一年几乎不能停电，否则就会给企业带来不可估量的损失，这就给用电检查提出了很高的要求。实际中对用户电力变压器、断路器进行停电检查的方
2、式已经行不通了。同时电力变压器、断路器是用户电力系统的重要设备之一,是用户变电站的核心设备,其运行状况直接关系着整个企业供电系统的安全经济运行。高压放电检测，不仅是高压设备出厂试验的主要项目，也是设备运行中进行绝缘试验的重要手段。近年来，许多出口产品的质量检验增加了高压放电检测项目。因此，我国对高压放电测试方法和技术进行了深入的研究。主要研究方向：用计算机辅助系统测量高压放电参数，利用各种谱图和统计量分析绝缘老化及缺陷；高压局部放电的在线检测技术和超声波定位；高压局部放电检测的抑制干扰问题。与其它检测方法相比,通过声音检测在很多方面有其独特的优点：1）可有效的避免电磁波的干扰，因此在电磁干扰严
3、重的场合应用。2）可以对高压断路器、变压器等高压设备进行连续实时在线检测。提高了供电可靠性。1 声音信号的采集1.1信号采集原理信号采集是高压放电检测的一个重要环节,它将接收到的高压放电声音信号以电信号的形式输出。在高压放电声音测量中,放电频率一般都在150kHz。虽然放电及其所产生的声发射信号具有一定程度的随机性,每次放电的声波信号频谱有所不同,但整个放电声波信号的频率分布变化范围不大,基本处于一定的频段之中。其次是符合香农采样定理，香农采样定理又称奈奎斯特（Nyquist）采样定理。一个存于0,fH的模拟信号，采样后，为了不失真地恢复该信号，则采样频率Fs必须满足fs2fH，一般应为10倍
4、。在传感器种类方面,以谐振式传感器最为多见；而光纤传感器具有体积小、重量轻、响应快、灵敏度高、抗电磁干扰能力强和能进行非接触测量等优点,有效减少了电磁干扰对局部放电信号测量的影响，近年来逐步得到推广。1.2信号采集过程为了保障放电检测装置的有效性，设置了高压放电装置，以便于每次试验之前保障可靠的高压放电，声音传感器检测高压放电以实现对放电现象的有效检测，采集过程中周围存在低频噪声，使用高通滤波去除低频信号，然后进行波谱分析。高压放电装置信号采 集处理频谱分析图1 测量放电声音信号流程图2.声音信号的分析2.1理论中的单个波形图变压器、高压断路器等高压设备出现局部放电现象时,总是伴随着脉冲电流、
5、电磁辐射以及声、光、热等现象。这是因为当介质内发生放电时,由于分子的激烈撞击,气泡的形成和发展,液体的流动以及固体材料的微小开裂,会产生一定的声音信号。通过研究发现,高压放电产生的这些声信号与放电的程度和类型存在一定的对应关系，有流体力学可知所发出的声音信号在接收后的波形图为尖波峰，有一个脉冲信号，然后逐渐下降消失。近似一阶脉冲响应，波形图如图2。图2 高压放电声音信号理论波形图2.2信号采集时的波形图放电信号检测电路在外加电压作用下，当击穿场强较低的气隙或气泡油膜中的局部场强达到气体或液体的击穿场强时，开始放电，并伴随着一定分贝的声波信号。在检测电压时，环境噪声是影响声音传感器灵敏度的重要因
6、素。根据统计可知,环境噪声一般为低频波,并且没有明显的延时现象；其波形与上述几种干扰波形有明显不同,易于识别。另外,声发射信号采集传感器在下雨等天气条件都会对声传感器的灵敏度产生影响。图3为环境噪声与高压放电信号同时存在时的波形图，图4是只存在环境噪声的波形图。图3 测量时的波形图图4 干扰时的波形图2.3 滤波后的波形图在日常生活中，存在的通常为低频噪音信号，而在高压放电产生的声音信号为高频信号，因此使用高通滤波器在滤波的过程能使高频信号通过，低频滤掉，处理后的波形如图5所示。图5 滤波后的波形图2.4波谱分析为了更好的分析信号，将信号源发出的信号强度按频率顺序展开，使其成为频率的函数，并考
7、察变化规律，称为频谱分析。对信号进行频谱分析，需对其进行傅里叶变换，观察其频谱幅度与频谱相位。对于数字信号，则可直接进行快速傅里叶变换，变换后的图形如图6所示。 图6 频谱图分析图6中的频谱图，频率主要集中在20150kHz，从频谱中可以准确的分析出放电现象的存在与否。3.结论：从以上分析可以看出,声音检测高压放电现象易于实现，但会受到距离的限制。随着科学的发展，声音检测设备和电子技术的快速发展,为声音检测方法的发展提供了发展空间。但在现场应用中,由于受到各种因素的干扰，检测高压放电现象在以后的发展中,不但要对检测系统硬件进行完善,还要从放电理论、识别算法、放电理论方面作进一步研究，从而提高诊
8、断结论的科学性、准确性。本理论可广泛应用于在大客户用电检查中对变压器、高压断路器、高压开关等高压设备的放电检测，具有很强的实时性、可操作性。同时在供电公司对以上相同设备进行检测时有很好的借鉴意义。参考文献1王国利,郝艳捧,李彦明.电力变压器局部放电定位方法的现状和前景。变压器,2001,38(11):22-27。2顾文业,王志敏,顾晓安.应用超声波测量法判断变压器内部局部放电的研究。噪声与振动控制,2003,(2):46-48。Editors note: Judson Jones is a meteorologist, journalist and photographer. He has f
9、reelanced 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 - Sp
10、utnik. 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 privati
11、zed 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
12、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
13、 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 als
14、o 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 h
15、is 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 super
16、sonic 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
17、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 th
18、e 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
19、 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
20、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.Skydiv
21、er 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 g
22、oes 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 s
23、uccessfully, 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 para
24、chute 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.