工作变形在变压器状态识别中的应用

首先从油浸变压器振动机理及振动传播途径出发,研究油箱壁振动用于判定变压器工作状态的可行性。然后论述目前常用的振动强度用于故障诊断的局限性,提出应用ODS(Operational Deflection Shapes)工作变形方法对变压器进行状态监测的方法。接着针对传统ODS方法难以定量判断的缺点,引入ODS定量判据RAC,运用线圈垫块掉落的故障模式开展试验分析,模态测试显示垫块掉落后,线圈前4阶固有频率下降约10%,证明故障模式成立。最后,通过试验求得故障状态与两次正常状态的ODS,用定量判据RAC对三次ODS进行分析,并区分出故障状态和正常状态ODS的差别,说明工作变形在变压器状态识别中有效可行。     

短路冲击下变压器绕组状态在线诊断

在线实时检测变压器绕组状态,对保障变压器正常运行尤为重要.绕组的振动信号能反映出绕组的状态,而这些信号能通过布置在变压器箱体上的加速度传感器测量到.通过对某大型变压器短路冲击实验的在线实时检测,利用振动烈度和基于时频分析的方法对变压器绕组的振动信号进行分析.研究表明,与常规电抗法检测相比较,用时频分析方法能更明确反映出变压器绕组的故障特征.     

《基于振动频响法的变压器绕组变形检测》

为了更加有效地识别绕组的变形故障,在基于机械振动频响法对变压器绕组进行检测的基础上,提出了标示绕组形变程度的振动频响曲线相关系数。通过对大型变压器的绕组进行人为故障设定,利用机械振动频响法对故障绕组进行检测,试验证明该振动频响曲线相关系数对判断变压器绕组变形具有较高的灵敏度。     

电力变压器状态检修及故障诊断方法探究

在电力变压器运行过程中,受多种因素影响难免出现故障,给人们的正常生产生活带来不良影响,为此,通过研究电力变压器故障诊断方法,可准确评估电力变压器运行状态,并采取有效措施将电力变压器故障带来的损失降到最低。笔者分析变压器状态检修与故障诊断要点,进行变压器状态检修的方法,进行初步探析。     

基于振动参数图像融合灰度共生矩阵的电抗器机械状态辨识方法

为更有效地监测电抗器的工作状态,提出一种基于振动参数图像融合灰度共生矩阵的电抗器机械状态辨识方法。首先对电抗器施加不同大小的电压、预紧力以模拟不同工况,在采用工作变形分析的基础上,利用灰度共生矩阵提取不同工况下工作变形分析云图的纹理特征,引入能够定量表征电抗器振动情况的振型相关系数,进而得到电抗器振动参数结合工作变形分析灰度图纹理特征的融合特征矩阵,最后利用支持向量机实现电抗器的状态辨识。通过模拟绕组松动故障试验,将所提方法与单一基于灰度共生矩阵的常规辨识方法进行比较,实验结果表明：所提方法能够有效地提取电抗器振动信号特征参量,且诊断精度相较于常规方法有明显提升,准确率可达93.6%。     

变压器故障检测技术

变压器的正常工作对于维持机械设备持续运转有着重要意义,进行变压器故障诊断能够及时排除潜在故障因素,确保变压器的可靠运行。本文分析导致变压器出现故障的常见因素,并介绍变压器故障检测的主要技术:红外热线法、振动分析法、频率响应法等,利用这些故障技术对变压器的日常工作进行检测与维护,能够有效延长变压器使用寿命,保证其工作效率不受到影响。     

变压器绕组松动的振动实验分析

变压器绕组故障是变压器故障中的重要部分,基于振动信号分析的方法可以实现变压器绕组运行状态的在线测量。阐述绕组的振动机理及传播路径,通过人为设置绕组松动故障,实测负载时不同松紧程度下的变压器油箱表面的振动信号。利用小波变换(WT)、经验模态分解(EMD)和总体经验模态分解(EEMD)三种方法对信号进行处理,并对信号能量熵求解,对比结果发现:针对绕组振动信号,三种能量熵变化规律与100 Hz处幅值均可作为初步判断绕组松动的指标。     

浅谈变压器固体绝缘故障的诊断方法

本文通过研究在故障涉及固体绝缘时,其它特征气体组分与CO、CO2间的伴生增长情况,提出了一种动态分析变压器绝缘故障的方法。并着手建立故障气体的增长模式,为预测故障的发展提供了新的判据。     

基于振动分布特征的电力变压器绕组故障诊断

振动分析法是实现电力变压器带电监测与故障诊断的重要手段,而基于振动分析法的故障诊断方法的关键在于从复杂的油箱壁振动信号中提取出状态特征(值或矢量)。传统的状态特征提取方法大多选取单个测点的振动信号进行时域或频域特征的提取,往往忽略了各测点间的振动分布特征。从振动重心的角度对振动分布的幅值重心及重心轨迹进行研究与分析,能够提出四个量化参数。在四个量化参数的基础上结合支持向量机分类算法提出基于振动分布特征的变压器绕组故障诊断模型。实际变压器的绕组故障实验以及十余台台电力变压器现场实测数据样本的分析与测试结果均表明,提出的振动分布特征及量化参数能够有效反映变压器绕组变形、压紧力松弛等机械结构变化,而基于振动分布特征的绕组故障诊断模型也可准确的对变压器绕组机械结构状态进行检测与诊断。     

刍议电力变压器故障类型分析及其诊断方法

变压器作为电力系统的重要设备,在电力系统中占据着非常重要的地位,其运行状态的好坏直接影响系统运行可靠性及其他电力设备的正常运行。通过对变压器的故障类型进行分析,并详细介绍常用的变压器故障诊断方法。     

Estimation of Parameters of Universal Distribution of Moments of Failure of Products

A method is proposed for estimating the parameters of a mixture of exponential and Weibull distributions for which the accuracy of preliminary estimates obtained by graphical analysis is refined in accordance with the criterion of maximum likelihood. The efficiency of the proposed method is supported by the results of statistical modeling.     

Assessment of intakes of mixtures of radionuclides

Australia has several uranium mines and a large number of mineral sand mines, with associated processing facilities. Exposures resulting from these mining and processing operations usually involve intakes of mixtures of radionuclides. This work describes the development of a suite of first order, linear compartment models, based on the ICRP Publication 66 respiratory tract model, and an analytical solution to the decay equations, for assessing the consequences of such intakes. The computer programs based on these models directly compute excretion, organ retention and organ and whole-body doses for intakes of either single radionuclides or any mixture of radionuclides belonging to the same radioactive decay chain. The intake can be via inhalation, ingestion or injection, and can be acute, chronic or of limited duration. The starting concentration and degree of secular (dis)equilibrium can be specified for each radionuclide. No assumptions need to be made about the relative magnitudes of the radioactive half-lives of the different nuclides.     

Analysis of the rate of propagation of the wave of change of boiling modes

An approximate analytical expression is derived for the velocity of the front of the wave of change of boiling modes on a rod and on a plate. The impact of the Thomson effect and of the heater orientation in the gravity field is included. Adequate agreement is demonstrated between the derived relations and experimental data.     

Evaluation of optical properties of highly scattering media by moments of distributions of times of flight of photons

A novel method for the determination of the optical properties of tissue from time-domain measurements is presented. The data analysis is based on the evaluation of the first moment and the second centralized moment, i.e., the mean time of flight and the variance of the measured distribution of times of flight (DTOF) of photons injected by short (picosecond) laser pulses. Analytical expressions are derived for calculation of absorption and of reduced scattering coefficients from these moments by application of diffusion theory for infinite and semi-infinite homogeneous media. The proposed method was tested on experimental data obtained with phantoms, and results for absorption and reduced scattering coefficients obtained by the proposed method are compared with those obtained by fitting of the same data with analytical solutions of the diffusion equation. Furthermore, the accuracy of the moment analysis was investigated for a range of integration limits of the DTOF. The moment analysis may serve as a comparatively fast method for evaluating optical properties with sufficient accuracy and can be used, e.g., for on-line monitoring of optical properties of biological tissue.     

Numerical study of methods of linearization of the output characteristics of radio-frequency sensors of the level of dielectric media

Different constructions of the sensing elements of radio-frequency level sensors based on sections of long lines are numerically investigated by means of the Matlab program for the purpose of minimizing the measurement error caused by the nonlinearity of the output characteristic. It is shown that the nonlinearity is lowest for U-shaped designs. The nonlinearity factor KN may be regulated by varying the capacitance of a correcting capacitor connected to the input of the sensing element and (or) the length of one of the sections of the long line. In selecting an optimal capacitance of the correcting capacitor KN ≤ 0.15% for control media with dielectric permittivity in the range 2.2–30.     

Possibilities of Decreasing the Errors of Determination of the Height of the Pole of a Sessile Drop of Melt

We analyze the possibilities of decreasing the errors of measuring the height of the pole of a sessile drop of melt above its equator by determining the position of the equator according to the midpoints of vertical chords of the image of the drop. The optimal distance between these chords and the edge of the image of the drop is chosen within 10–20% of the radius of the equator. The proposed method guarantees the same level of errors of evaluation of the height of the pole and the radius of the equator, which enables one to substantially increase the accuracy of evaluation of the capillary constant and the surface energy of the melt according to the geometric parameters of the sessile drop.     

Analysis of anisotropy of properties on the basis of studies of texture of coarse-grained ingots of thermoelectric materials

An analysis of anisotropy of the properties of a Bi₂Se_0.3Te_2.7 solid solution was carried out using construction of demonstrative surfaces for thermoelectric effectiveness and thermal expansion coefficients. It is shown that the texture is an important factor forming anisotropy of properties and technological fitness of ingots for manufacturing modules. Anisotropy of properties based on the studies of the ingot textures obtained using the float-zone method and Bridgman method (growing thermoelectric plates in a flat cavity) was studied.     

Estimation of potentialities of methods of summation of direct measurement errors

Conventional methods for summation of direct measurement errors are considered. Conditions under which these methods provide consistent results are stated. It is proposed to utilize for characteristic of the total error, its interval estimator or the half-sum of the value obtained by adding up its arithmetic and geometric random errors.Translated from Izmeritel'naya Tekhnika, No. 4, pp. 10–12, April, 1995.