Analysis of Excitation Characteristics of Ultra High Frequency Electromagnetic Waves Induced by PD in GIS

The understanding of the excitation mechanism of ultra high frequency (UHF) electromagnetic waves (EW) is essential for ap- plying UHF method to partial discharge (PD) detection. Since the EW induced by PD in gas insulated switchgear (GIS) contains not only transverse electromagnetic (TEM) wave, but also high-order transverse electric (TE) and high-order transverse magnetic (TM) waves, we analyzed the proportions between the TEM wave and the high order waves, as well as the influence of the PD position on this proportion, using the finite different time domain (FDTD) method. According to the unique characteristics of the waves, they are separated only ap- proximately. It is found that the high-order mode is the main component, more than 70%, of the electric field around the enclosure of GIS, and that with the increasing distance between PD source and inner conductors, the low frequency ( below about 800 MHz) component of EW decreases, but the high frequency component (above 1 GHz) increases, meanwhile the proportion of high-order components in EW could reach 77% from 70%. It concluded that the closer the PD source to the enclosure is, the easier high order EW may be excited.

THE STUDY ON MEASURING TECHNIQUE OF PARTIAL DISCHARGE IN GAS INSULATED SWITCHGEAR USING ULTRA HIGH FREQUENCY METHOD WITH EXTERNAL SENSORS

Objective In order to find early latent faults and prevent catastrophic failures, diagnosis of insulation condition by measuring technique of partial discharge(PD) in gas insulated switchgear (GIS) is applied in this paper, which is one of the most basic ways for diagnosis of insulation condition. Methods Ultra high frequency(UHF) PD detection method by using internal sensors has been proved efficient, because it may avoid the disturbance of corona, but the sensor installation of this method will be limited by the structure and operation condition of GIS. There are some of electromagnetic (E-M) waves leak from the place of insulation spacer, therefore, the external sensors UHF measuring PD technique is applied, which isn't limited by the operation condition of GIS. Results This paper analyzes propagated electromagnetic (E-M) waves of partial discharge pulse excited by using the finite-difference time-domain (FDTD) method. The signal collected at the outer point is more complex than that of the inner point, and the signals' amplitude of outer is about half of the inner, because it propagates through spacer and insulation slot. Set up UHF PD measuring system. The typical PD in 252kV GIS bus bar was measured using PD detection UHF technique with external sensors. Finally, compare the results of UHF measuring technique using external sensors with the results of FDTD method simulation and the traditional IEC60270 method detection. Conclusion The results of experiment shows that the UHF technique can realize the diagnosis of insulation condition, the results of FDTD method simulation and the result UHF method detection can demonstrate each other, which gives references to further researches and application for UHF PD measuring technique.

SIMULATION OF TEMPERATURE FIELD IN ULTRA-HIGH FREQUENCY INDUCTION HEATING AND VERIFICATION

An experimental and numerical study on the temperature field induced in the ultra-high frequency induction heating is carried out.With an aim of predicting the thermal history of the workpiece,the influence factors of temperature field,such as the induction frequency,the dimension of coil and the gap between coil and workpiece,are investigated considering temperature-dependent material properties by using FLUX 2Dsoftware.The temperature field characteristic in ultra-high induction heating is obtained and discussed.The numerical values are compared with the experimental results.A good agreement between them is observed with 7.9% errors.

GIS绝缘子表面金属异物附着缺陷局部放电UHF信号间歇性与有效检出率分析

局部放电特高频(UHF)方法检测局部放电(PD)是当前评估气体绝缘开关设备(GIS)状态和绝缘性能的重要手段之一。本文为解决局部放电UHF检测出现大量漏报和误报的问题,通过开展GIS绝缘子表面金属异物附着缺陷长期恒压实验,结合现有UHF检测策略对放电信号的成功捕捉概率进行分析,从检测时长和检出阈值两方面对现有UHF信号的检测策略提出了优化方案。结果表明:绝缘子表面金属异物附着缺陷局部放电具有间歇性特点,现有UHF带电检测及在线监测策略对放电的检出概率均不高。针对带电检测策略进行优化,延长检测时长至2247s,有效放电的捕捉概率可达85%;针对在线监测策略进行优化,延长形成一个局部放电事件(PDEvent)的测量时间和降低其检出阈值皆可增大PDEvent的检出概率,工程应用中可选择合适的测量时间和检出阈值相组合的方式来进行间歇性放电的检测。

油纸绝缘缺陷局放UHF抗干扰定位及优化布置方法

特高频(ultra high frequency,UHF)局放检测是变压器油纸绝缘缺陷定位的常用方法,实际应用过程中局放定位准确性易受噪声和传感器布置方式影响。为保证变压器油纸绝缘缺陷局放定位检测有效性,文中首先建立油纸绝缘缺陷UHF局放定位检测平台,在常规K-means方法的基础上,提出基于修正聚类分界的变压器油纸绝缘缺陷局放抗干扰定位方法,有效降低了定位误差。然后针对样本聚类分界混叠问题,选择最优修正系数L为1.1时,UHF局放定位误差可减小至0.1 m内,验证了文中方法的有效性。最后分析不同传感器布置方式的定位误差变化规律,提出变压器油纸绝缘缺陷检测用UHF传感器优化布置方案,可为变压器局放在线监测传感器布置及定位提供参考。

The Principle and Practice of the Deviation of Power Frequency Component Relay on High Voltage Transmission Line

The research and development of ultra high speed protective relay of transmission line has got great interest and attention of protective relay engineer over the world. Several versions and schemes of ultra high speed relay have been studied and designed in recent twenty years. But only a few of them have got actual apiication in the power system. The relay based on the deviation of power frequency component (DPFC) can get very high reliability with ultra high speed so it has got wide application in Chinese power system. Thousands relay sets have been applied and its operation experience verifies their excellent performance. This paper summarizes the course of the development of the uItra high speed protective relay and compares the merits and defects of the main schemes which have been developed. The principle and successful pratice of the ultra high speed protection based on DPFC reIay are introduced.

Structure optimization of connection frames based on frequency sensitivity in macro-micro motion platforms

High-performance connection frames are of great significance for ultra-high acceleration and ultra-precision positioning in macro-micro motion platforms. This paper first takes the connection frame as a research object,builds a finite element model(FEM) of the natural frequency of the frame, and then verifies the correctness of this model. The frequency sensitivity method is then used to perturb the structural parameters of the FEM of the connection frame, and the sensitivities of the first-order natural frequency and mass of the corresponding structural parameters are obtained by calculation and analysis. The design variables are also determined. The natural frequency is used as the optimization objective, and the design parameters and mass of the connection frame are constrained. The structural parameters of the connecting frame are obtained through optimization, and the model is built and verified by experiments. The results show that the first-order natural frequency of the connecting frame is effectively improved by the frequency sensitivity method, avoids resonance between the connecting frame and the voice coil motor, and realizes the lightweight design of the connection frame. This research provides a reliable basis for the stable operation and ultra-precision positioning of ultra-high acceleration macro-motion platforms.

超小型内置柔性宽频带UHF单极子天线传感技术

特高频(ultra high frequency,UHF)法是电力设备局部放电(partial discharge,PD)绝缘缺陷常用的检测方法,在内置安装空间受限的情况下保证UHF天线具有良好的PD高频电磁波信号感知性能至关重要,基于聚亚酰胺(polyimide,PI)柔性基底设计了一种小型化UHF单极子天线,尺寸仅为58 mm×36.8 mm×0.3 mm,相较于传统单极子天线结构缩小了50.4%,并且通过对辐射区镂空和弯折处理改善了天线的低频性能。仿真和实测表明,设计的柔性天线在绝缘油和SF6绝缘气体中的有效带宽分别达到360 MHz~2.35 GHz与440 MHz~1.78 GHz,可全向接收PDUHF信号且弯曲形变后天线能保持良好的辐射性能。最后,搭建220kV真型气体绝缘组合电器和变压器PD模拟实验平台,对柔性天线在不同绝缘缺陷下的PD检测性能进行实测。结果表明,柔性天线内置后能有效检测到低放电量下的PD UHF信号,具有较高的灵敏度,可满足电力设备PD检测需求。

The effect of frequency and sample shape on fatigue behaviors of DZ125 superalloy

The effect of frequency and sample shape on fatigue behaviors of DZ125 superalloy are systematically studied.The results show that fatigue fracture still occurs above the cycle of 10~8 for tests carried out at the frequency of f=20 kHz and stress ratio R =-1,so the traditional fatigue limit at cycle of 10~7 is not appropriate for fatigue design.Fatigue fracture surfaces are perpendicular to stress axis for cylindrical and plate specimens,and the fatigue cracks originate from the extra surface of the specimens.Fatigue crack is apt to propagate from cutting direction to forward direction,which occurs mainly in the second propagation stage at higher stress amplitude. There is an obvious frequency effect for DZ125 superalloy.The higher the test frequency is,the more serious the effect of frequency on fatigue behaviors of the alloy.After the frequency correction,the ultra-high cycle fatigue S-N curve well coincide with the traditional fatigue S-N curve.

智慧图书馆建设背景下的文献无感借阅服务应用研究——以重庆图书馆开放式无感智慧借阅系统实践为例

无感借阅技术在图书借阅环节的应用,使公共图书馆具备了在读者无感知状态下为其提供文献借阅服务的能力。目前,我国已有个别公共图书馆率先研发并开通了无感借阅服务,但从实现方式、识别率、方便程度上与“真”无感借阅尚有较大差距。文章以重庆图书馆研发、投用开放式无感智慧借阅系统为例,研究、探讨开放式无感借阅技术应用于图书借阅服务环节的技术架构、实现路径,以及在此过程中的关键问题、实施成本。通过开放式无感智慧借阅系统的实践及完善,最终形成运行稳定、低成本、可复用的智慧图书馆应用,为行业应用无感借阅提供范例。

激光毫米波共孔径干扰仿真及试验研究

对合束镜材料、厚度、尺寸等特征参数进行了仿真优化设计和试验验证,确定石英为合束镜优选基底材料,实现905 nm/1064 nm超高重频激光与8 mm毫米波波束共孔径发射。905 nm激光重频22.4 MHz,合束效率优于87.1%。针对905 nm激光引信模拟器实测干扰距离178.5 m,针对RCS=100 m^(2)目标毫米波等效最小干扰距离202 m。结果表明,研究为对抗复合探测威胁目标提供了一种新的技术途径,实现了激光毫米波波束共孔径高效发射,在装备研制中具有较高应用价值。

一种基于相控阵列天线的超高频射频识别相对定位方法

针对已有相对定位方法存在环境依赖程度大、定位精度低等问题,提出一种基于相控阵天线的超高频(UHF)射频识别(RFID)相对定位方法,该方法通过调节相控阵天线的激励参数来改变天线的辐射方向,以获取目标标签的收信场强轮廓,有效降低了系统对环境和场地的依赖程度;同时,提出一种基于轮廓陡峭程度的相对位置估计方法,该方法首先利用轮廓最高点的时间戳信息将目标标签分为两组,然后计算每一组标签的整体轮廓陡峭程度进而估计其相对位置。仿真结果表明:相比于传统相对定位方法,所提相对定位方法能够有效提高定位精度,降低排序偏差;在信噪比为20~30 dB时,性能提高了7.7%~21.6%。上述结果证实了本文方法的有效性。

基于NMD算法的水电高占比电网低频振荡模态辨识

水电高占比电网中的调速控制问题会导致低于0.1 Hz的超低频振荡,与低频振荡混合加大了低频振荡参数辨识的难度。因此本文提出一种基于自适应的时频分析方法-非线性模态分解(Nonlinear mode decomposition,NMD)来对低频振荡进行参数识别。该方法能够根据信号结构提取时频脊线,估得谐波参数,辨别出对应分量真谐波,消除虚假模态分量。并利用提取出分量的频谱熵特征来设定一个停止分解准则,使分解出的非线性模态分量(Nonlinear mode,NM)具备实际物理意义。对每个NM分量进行Hilbert变换(Hilbert transform,HT)求取振荡参数。最后通过自合成测试信号仿真算例、四机二区系统仿真算例和电网实测算例验证所提方法可行性和有效性。

深井超深井大尺寸井眼钻具疲劳失效分析与防控

地球深部蕴藏着丰富的油气资源,随着深井超深井钻井数量的递增,钻具失效(断钻具、钻具刺漏)事故呈现逐年递增趋势。为进一步明确深井超深井大尺寸井眼钻具失效原因、减少钻具失效事故,梳理了近年来中国石油西部三大油田钻具失效情况及特征,并以西部油田某口典型超深井?444.50 mm井眼连续5次断钻具事故为对象开展原因分析。首先基于弹性动力学密哈顿原理(Hamilton’s principle)和纽马克方法(Newmark-β)建立了钻具动力学模型,结合雨流法和Miner疲劳损伤累积理论实现对钻具运动、受力及疲劳寿命的定量评价,并验证了模型的准确性,最后提出了大尺寸井眼预防断钻具配套工艺措施。研究结果表明:(1)深井超深井中钻具失效主要发生在上部大尺寸井段,失效位置多集中在下部钻具接头或本体尺寸较小的薄弱位置;(2)因钻具横向振动诱发高频弯曲应力是导致钻具疲劳失效的主要因素,持续剧烈的横向振动在数小时内会导致钻具疲劳失效;(3)提高下部钻具组合刚度、使用“高钻压+低转速”参数钻进有助于降低钻具横振强度;(4)因钻具组合刚度偏小、钻井参数不合理导致下部钻具剧烈横向振动,叠加“中性点”在钻具接头及本体尺寸较小等薄弱位置反复交替,是典型案例井连续断钻具的直接原因。结论认为,建立的模型可以定量评估钻具疲劳失效情况,提出的预防措施可为深井超深井大尺寸井眼预防钻具失效提供技术参考。

基于无源超高频RFID的农产品包装智能定位方法

射频识别(radio frequency identification,RFID)技术为工业物联网(industrial internet of things)带来了巨大的进步,作为实现智能仓储的关键技术之一,广泛应用于库存管理和智能定位等场景,然而现有的绝对/相对定位方法易受仓储环境、包装材料、货架材质等因素影响。为了进一步提升室内定位精度,该研究提出了一种基于接收信号强度指示器(receive signal strength indicator,RSSI)和测量相位融合的无源RFID定位方法(RFID positioning based on received signal strength indicator and phase measurement,RP-RaP)。首先,使用MATLAB软件进行仿真模拟,在已知测量相位统计学分布的前提下,采用最大似然估计法对标签进行水平定位,同时基于双天线阅读器所测得的RSSI差值对标签进行垂直定位,实现了无源超高频RFID标签的水平和垂直定位仿真。其次,以农产品包装场景为例,在仓库中搭建射频定位测试系统,通过滑轨搭载射频阅读器及天线,对货架物品上的贴附标签进行水平和垂直定位分析,最后将无源标签分别贴附于金属盒、油桶、纸箱、面粉袋和大米袋,并以未贴附标签的测量结果作为对比。试验结果表明,与传统的室内定位算法LANDMARC相比,RP-RaP定位精度明显提升,平均水平和垂直定位精度分别达到94.6%和94.3%,基于接收信号强度指示器和测量相位融合的定位方法有效提升了农产品包装定位精度。研究结果可为大型农产品仓储智能化管理与应用提供参考。

基于PMU的特高压直流输电系统孤岛运行控制方法

受特高压(Ultra-High Voltage,UHV)直流输电系统自身运行特点的影响,孤岛运行阶段的环流难以实现快速维稳,提出基于电源管理单元(Power Management Unit,PMU)的特高压直流输电系统孤岛运行控制方法。考虑输出电压的角度会受电压源换流器(Voltage Sourced Converters,VSC)的影响发生瞬时改变,提出有功-相角下垂控制方法,逆变器通过微型PMU的同步信号,确定派克变换的参考坐标系,将特高压直流输电系统孤岛运行阶段的目标维持频率作为控制基准。以调整特高压直流输电系统中所有分布式发电装置(Distributed Generation,DG)的相角参考值处于一致状态为导向,结合微型PMU测得的公共母线电压相角参数,控制有功补偿量。在测试结果中,环流达到0值后出现的偏离情况程度稳定在10.0 VA以内,并在测试后的0.8 s内达到0稳态。

高压开关柜局部放电UHF在线监测系统的研究

为了提高高压开关柜运行的安全性,笔者在介绍超高频法局部放电在线监测系统的基础上,设计制作了4种典型放电模型,并应用此在线监测系统对高压开关柜进行了局部放电试验研究,获取了大量放电谱图和放电脉冲波形,并对放电的相位特征进行了分析。结果表明:该系统具有抗干扰能力强、工作稳定性好等优点,满足高压开关柜局部放电在线监测的要求。

基于方形螺旋谐振器的紧凑型RFID标签天线

设计了一种小型化超高频(UHF,ultra-high frequency)射频识别(RFID,radio frequency identification)标签天线。该天线由内外两个方形螺旋谐振器短接构成,通过改变外圈螺旋谐振器的边长和内外圈螺旋谐振器的间距,可以有效调节标签天线的谐振频率。仿真结果表明,标签天线阻抗匹配良好,频带范围覆盖整个超高频频段(840~960 MHz),总尺寸为7.60 mm×7.60 mm×0.05 mm,比传统螺旋谐振器(SR,spiral resonator)天线小96%。测试结果表明,在4 W有效全向辐射功率条件下,标签天线在910 MHz处读取距离达到最大。所提小型化超高频射频识别标签天线具有尺寸小、频带宽、成本低和易于批量制作的特点,适用于对尺寸要求较小的应用环境。

GIS中典型局放缺陷的UHF信号与放电量的相关分析

超高频(UHF)信号与放电量的关系是局部放电UHF检测研究的难点问题,为了解GIS局部放电UHF法的检测结果与脉冲电流法的参量之间的关系,通过4种典型缺陷的局部放电模型的实验研究,比较了UHF信号的能量、二次积分、峰值电压、峰峰值、波面积等参量与放电量及放电量平方之间的联系。研究表明,UHF信号能量与其放电量平方的线性关系均具有最高的可决系数,即UHF信号能量与放电量平方之间存在线性关系;得到了UHF信号能量与其放电量之间的最佳回归曲线。研究结果对用超高频法定量检测电力设备局部放电具有重要的参考价值和指导作用。

油中局部放电UHF频带选取及干扰的抑制

为消除变压器局部放电对现场测量的干扰,在对绝缘油中局部放电特高频信号频谱特征研究基础上,给出了特高频法测量绝缘油中局部放电的频率范围;为满足实际测量要求,采用包络检波方法对放大后的特高频信号进行降频处理;同时,提出了高频与特高频联合测量方法,用来消除现场局放测量中的干扰。对现场测量数据的处理结果表明,所提出的方法可很好抑制干扰信号。