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《Electric Power Systems Research》2005,73(2):159-168
Electrical trees were generated experimentally in the actual 33 kV underground XLPE cable insulation material under the AC voltages. A tree like structure and a bush type of tree structure can form from the point of defect site under the AC voltages. Acoustic emission technique was adopted to identify the point of inception, propagation and termination of electrical trees. A variation in the dominant frequency content of the acoustic signal was observed as and when the tree propagates in the insulation structure. The characteristic variation in the magnitude of the acoustic emission signal with time, indicates that tree propagation as an intermittent growth process. The energy content of the acoustic signal characterizes that the energy released due to partial discharges, at every step growth of the tree structure is not the same. The partial power measurement in the present study provides an indication to the growth process of electrical trees and to the near point of failure of polymer insulation material due to electrical treeing. 相似文献
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为了获取直升机动部件疲劳损伤声发射信号的传播特性,搭建了声发射数据采集系统,对直升机动部件常用碳纤维材料试件和蜂窝材料试件进行了传播特性断铅试验,利用谐波小波包分析了声发射信号在各个频带上的衰减特性,克服了传统小波包分析能量泄露、频带选取不灵活、不同层频率分辨率不同的缺点.研究结果表明对于所研究两种试件,100 ~ 200 kHz频带的衰减特性与原始信号基本一致,可以代替原始信号进行定位和损伤识别研究,频率越高,衰减越快,衰减较大的无损检测场合,适合选择较低频率范围提取信号特征,对于所研究碳纤维材料试件,200 mm之后声发射信号衰减特性偏离理想衰减特性很大,限制了传统声发射源定位方法的应用. 相似文献
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电力变压器绝缘局部放电的声发射频谱 总被引:2,自引:0,他引:2
本文针对电力变压器绝缘局部放电的几种典型形式进行了实验室模拟,用微机测量系统采集了六种模型局部放电的声、电信号,得出了声发射频谱、声、电信号时延关系,以及在较厚的绝缘纸内发生放电时声信号的衰减规律和频谱的变化。用声发射法在线监测变压器的局部放电时,变压器铁心的磁噪声是稳定而严重的干扰信号、本文分析了磁噪声信号的时域及频域特征。基于变压器绝缘局部放电模型的声频谱和磁噪声的频谱,本文给出了用声发射法检测电力变压器绝缘局部放电的频带范围,并论述了根椐不同的放电声频谱判断故障类型的可能性。 相似文献
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V. G. Petrosyan T. H. Hovakimyan E. A. Yeghoyan H. T. Hovhannisyan D. G. Mayilyan A. P. Petrosyan 《Thermal Engineering》2017,64(1):1-5
This paper is dedicated to the creation of a facility for the experimental study of a phenomenon of background acoustic emission (AE), which is detected in the main circulation loop (MCL) of WWER power units. The analysis of the operating principle and the design of a primary feed-and-blow down system (FB) deaerator of NPP as the most likely source of continuous acoustic emission is carried out. The experimental facility for the systematic study of a phenomenon of continuous AE is developed. A physical model of a thermal deaerator is designed and constructed. A thermal monitoring system is introduced. An automatic system providing acoustic signal registration in a low frequency (0.03–30 kHz) and high frequency (30–300 kHz) bands and study of its spectral characteristics is designed. Special software for recording and processing of digitized electrical sensor signals is developed. A separate and independent principle of study of the most probable processes responsible for the generation of acoustic emission signals in the deaerator is applied. Trial series of experiments and prechecks of acoustic signals in different modes of the deaerator model are conducted. Compliance of basic technological parameters with operating range of the real deaerator was provided. It is shown that the acoustic signal time-intensity curve has several typical regions. The pilot research showed an impact of various processes that come about during the operation of the deaerator physical model on the intensity of the AE signal. The experimental results suggest that the main sources of generation of the AE signals are the processes of steam condensation, turbulent flow of gas-vapor medium, and water boiling. 相似文献
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Sakoda T. Arita T. Nieda H. Ando K. Otsub M. Honda C. 《Dielectrics and Electrical Insulation, IEEE Transactions on》1999,6(6):825-830
In order to diagnose the deterioration of insulation and evaluate its location in oil-filled pole transformers, measurements of elastic waves brought by corona discharges in oil were performed, based on an acoustic emission (AE) technique. The detected signals in these measurements were analyzed by means of a fast Fourier transform (FFT) and their properties were discussed theoretically. It was found that the AE signals due to the Lamb waves of symmetric mode caused in a thin steel tank could be recognized easily by the FFT analysis of initial stages of the detected AE signals. This suggests that the accuracy on location of the AE sources in the transformer would be improved. Also, it was shown that a low pass filter was effective in improving the location accuracy 相似文献
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以绝缘子放电声发射波的时域主成分值作为特征量,进行常见3类放电的识别研究时,因放电间歇性、放电声波中数据坏点的影响,导致放电识别效果欠佳。故笔者将绝缘子放电声发射波看作一分形体,提取其分形维数作为识别特征量。具体选取了在绝缘子3类放电上分布差异较大的分形关联维数作为识别放电的特征量,通过研究测试,总结了各类放电关联维数的分布范围及规律。最后,设计BP网络,进行识别测试,结果表明,与时域主成分值相比,以关联位数作为识别特征量,更能准确、有效地识别绝缘子的放电类型,识别正确率达到89%左右。 相似文献
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Masashige Takaoka Kazuki Inohata Takuma Miyake Daisuke Tashima Masahisa Otsubo Toshio Bouno 《Electrical Engineering in Japan》2011,174(1):33-39
The establishment of an early trouble diagnosis system is needed in order to prevent damage to wind turbine generators. Therefore, acoustic emission (AE) signals resulting from damage to a wind blade were detected with an AE sensor installed on the body of the wind turbine generator and on the mounting pole. In this study, the length of a blade of a micro wind turbine generator was varied to simulate trouble at constant wind velocity. The AE signals which occurred at this time were measured with an AE sensor. The signal was processed by FFT analysis, and the change of spectral strength was examined. A trouble diagnosis technology for 50‐W‐grade micro wind turbines generator was then developed. A method of counting the number of occurrences of above‐threshold AE signals was suggested by the wave pattern of the AE signals. It was found that the number of occurrences could be used as a standard to judge the normality or abnormality of 50‐W‐grade micro wind turbine generators. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(1): 33–39, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.21017 相似文献
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转子碰摩声发射源定位中的
广义互相关时延估计研究 总被引:9,自引:0,他引:9
具有多模态波特征的转子系统碰摩声发射源信号在复杂体波导传播过程中,由于各模态波的速度差异及波形变异,常规的相关分析算法难以得到准确的时间差而无法进行准确的声源定位。针对这一问题,引入广义互相关(generalized cross correlation,GCC)时延估计方法计算声发射信号的达到时间差。基于模态声发射和随机过程理论建立声发射信号的传播模型,为消除噪声对定位的影响,提出基于相同分数阶因子和不同分数阶因子的最佳线形分数傅里叶(Fourier)变换域滤波的GCC时延估计;针对声发射信号在传播中因频散效应引起的波形变异,导致无法获取最大相关点的问题,提出对信号进行分段相关乘积处理和分段相关指数变换处理的改进方法。实验结果表明,GCC时延估计对在复杂体机构中传播的声发射信号能获得较好的相关性,具有较高的定位精度。 相似文献
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小波包在声发射信号特征提取中的应用 总被引:4,自引:3,他引:1
在分析典型声发射(AE)信号特征的基础上,根据机械故障或损伤引发的AE信号的特征提取原理,首次提出AE信号的小波包特征提取分析法。该方法利用小波包将信号按任意时频分辨率分解到不同频段的特点,可从AE信号中提取和重构出所需的特定时频段(点)上的特征信号,解决了不能从噪声大、频带宽和数据量大的实测AE信号中有效提取特征信号的难题。介绍了该方法的具体算法,并通过仿真研究了该方法在强噪声背景下提取特征信号的能力;将其用于声发射检测的滚动轴承损伤类型及部件的识别,诊断结果十分清晰、可靠和精确。仿真和实验研究均表明了AE信号的小波包特征提取分析法能有效应用于基于声发射技术的状态监测和故障诊断。 相似文献
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电磁声发射技术是一种新型的无损检测技术,通过对导电部件进行电磁加载产生洛仑兹力,进而激发声发射效应,并通过这个效应来进行无损检测。传统的电磁声发射技术使用电极直接加载的方式引入电磁激励,存在激励电流过高、加载不方便等缺点。本文使用电磁线圈引入电磁激励,利用电磁线圈激发的瞬时电磁场加载在缺陷处,激发缺陷自身产生声发射信号,以提高对金属薄板中微细缺陷的检测能力。针对电磁声发射技术要求电源的输出功率较大、输出脉冲数可以调整并且电路的输出频率变化较大的特点,本文设计了一种基于直接数字频率合成技术的新型涡流激励电源。该电源主要包括信号产生、功率放大、串联谐振三部分,其中控制电路为核心部分。实验结果证明,该系统工作稳定,参数调节方便,能够满足电磁声发射检测对激励源提出的要求。 相似文献
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介绍了采用声发射无损检测技术对制氢站6台多层包扎式氢气储罐在带氢介质下升压进行在线检验和安全评定的方法。试验说明应用声发射技术可以在不停运的情况下对无法进行内部检验的在用容器进行检验,保证了容器的安全使用,并为声发射检验技术在电力系统的推广应用提供了成功的经验和依据。 相似文献
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The electromagnetic effect of cooling fins is studied by solving Maxwell equations numerically using a FDTD method under high‐frequency operating conditions. The fin is attached to a square IC chip to form a package. The overall size of the package is 25 mm × 25 mm × 17.5 mm. A smooth compact pulse with a reference frequency of either 1 or 2.5 GHz is used as the excitation source of EM waves. Six fin configurations are investigated. Computational results indicate that a fin can act as an antenna. For the present type of excitation source, resonance could occur roughly at frequencies of 2.5, 5 and 7.5 GHz, depending on the source reference frequency and fin geometries. Thus, fin effects should be considered in the electrical design phase since noises could be induced in the circuit due to the presence of fins. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
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Chikako Yokota Kazushi Ishiyama Ken Ichi Arai 《IEEJ Transactions on Electrical and Electronic Engineering》2007,2(4):436-439
This paper describes a cantilevered actuator driven by magnetostriction in a low magnetic field. The dimensions of the two‐layer actuator were 1 mm × 5 mm, and amorphous FeSiB was used as the positive magnetostrictive material. The theoretical formulas for the amount of displacement and force of the actuator were obtained. In the experiment, a nonmagnetic polyimide film material and a negative magnetostrictive Ni film material were used as the substrates. The change in the characteristics of the actuator caused by changing the substrate was examined with theoretical formulas and experiments. It is shown that the actuator with Ni as the substrate was designed to obtain the largest displacement and the largest force. © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc. 相似文献
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For partial discharge, PD, allocating utilizing acoustic emission, AE, sensors, the arrival time of acoustic waves to the sensors forms the calculation basics, therefore, it is crucial that distance calculations are based on direct acoustic path. Considering structure-borne waves of higher speed, this would imply an incorrect distance between the source and sensor, because, AE signals of indirect path me be considered as AE signals of direct path. Therefore, a heuristic algorithm has been developed to consider the possible indirect paths. By comparing the time taken in each path of propagation, to reach the specified sensor location, the indirect path of shortest time for AE signal is determined. For experimental verification, a test oil chamber has been fabricated. PD signals are generated at different points inside the tank. The estimation results of algorithm have been compared with results of classic Time Difference of Arrivals method, TDOA. The proposed method considerably increases the PD allocation precision. 相似文献
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离散分数余弦变换在碰摩声发射信号降噪中的应用 总被引:1,自引:0,他引:1
声发射信号经常淹没在各种复杂的非平稳噪声中,使得对有用的声发射的识别非常困难,因此,在声发射识别时进行信号增强成为诸多研究者的关注热点。离散余弦变换是声信号增强的有效方法。基于态函数,给出了分数余弦变换的新定义,提出三周期离散分数余弦变换方法,介绍了基于三周期离散分数余弦变换的声发射信号增强算法和改进算法的推导过程。实验数据为在转子实验台上采集的碰摩声发射信号,通过在该信号上叠加高斯白噪声和非平稳噪声来获得模拟的严重噪声污染的声发射信号,然后用增强算法及改进算法对该信号进行降噪处理和声发射信号识别。实验结果表明:两种算法对多种非平稳噪声环境下的碰摩声发射信号均能取得较好的降噪效果,且优于离散余弦变换,是声发射信号识别的有效途径。 相似文献