Sweep frequency response analysis (SFRA) for the assessment of winding displacements and deformation in power transformers

The sweep frequency response analysis (SFRA) is an analysis technique for detecting winding displacement and deformation (among other mechanical and electrical failures) on power and distribution transformers. Nowadays, there is an increasing interest in SFRA method because of its sensibility in detecting mechanical faults without opening the unit. SFRA as a diagnostic technique must integrate both the off-line measurements and the interpretation of the data in order to provide an assessment of the condition of the windings. However, guidelines for the measurement and record interpretation are not available. The evaluation is presently done by experts in the topic through the visual inspection or with the help of statistical parameters such as the correlation coefficient and the standard deviation. However, criteria like the limits of normal variation of the parameters, and the features observed in the records in the presence of a determined type of fault could not to coincide. Although, there are some proposals for making the interpretation more objective, neither of them integrate human expertise along with the different kind of parameters obtained from the evaluation of the records in a diagnostic model. This paper presents a survey on the alternatives in the measurement techniques and interpretation of SFRA measurements, describing some sources of uncertainty in applying this methodology.     

基于纳秒级IFRA方法的变压器绕组变形检测研究

脉冲频率响应分析法(IFRA)相比广泛应用于离线检测的扫描频率响应分析法(SFRA)在变压器绕组在线监测中有更好的适用性。目前,离线IFRA方法的激励脉冲波形特征尚未标准化,其可靠性、灵敏性、重复性需要深入研究。通过实验提取了适合于变压器绕组变形IFRA检测的激励脉冲波形特征,采用分频段分层小波阈值去噪提取IFRA频响曲线。在一台配电变压器上模拟了三种程度的轴向绕组变形,在两种接线方式下,均依次用IFRA方法和SFRA方法进行检测,并用斯皮尔曼相关系数和欧式距离对IFRA频响曲线进行量化分析,验证了纳秒级IFRA方法的可靠性和灵敏性,并进行了重复性验证。     

Regulation quality for frequency response of turbine regulating system of isolated hydroelectric power plant with surge tank

Aiming at the isolated hydroelectric power plant (HPP) with surge tank, this paper studies the regulation quality for frequency response of turbine regulating system under load disturbance. Firstly, the complete mathematical model of turbine regulating system is established and a fifth order frequency response under step load disturbance is derived. Then, the method of primary order reduction and secondary order reduction, for this complete fifth order system of frequency response, is proposed based on dominant poles. By this method, the complete fifth order system is solved and the regulation quality for frequency response is studied. The results indicate that the complete fifth order system always has a pair of dominant conjugate complex poles and three non-dominant poles. The primary fourth order equivalent system, which is obtained by primary order reduction, keeps the dominant poles almost unchanged, therefore it can represent and replace the complete fifth order system and it is obviously superior to other fourth order systems. The primary fourth order equivalent system is superimposed by two second-order subsystems, one of them is corresponding to two non-dominant real poles (i.e. head wave) and the other one is corresponding to a pair of dominant conjugate complex poles (i.e. tail wave), respectively. In the fluctuation process of frequency response, head wave decays very fast and works mainly in the beginning period while tail wave decays very slowly, fluctuates periodically and works throughout the period. The secondary order reduction of complete fifth order system can be conducted by using the second order system of tail wave, which is the main body of frequency response, to represent the fluctuation characteristics. The most important dynamic performance index that evaluates the regulation quality, i.e. settling time, is derived from the fluctuation equation of tail wave. The different characteristic parameters of turbine regulating system have different influences on the change rules of head wave, tail wave and settling time.     

Efficient computation of frequency response of digital networks

A major requirement in the analysis of multi-input-multi-output digital networks is to compute the frequency response at a large number of points from a knowledge of the graph of a network with specified input and output nodes. Though the usual method of analysis by solving linear equations is more efficient than matrix inversion, solution of linear equations at each frequency may still require a large amount of computation. A more efficient method is to determine the poles and zeros of the desired system function and then calculate the frequency response from them. Though poles of the system function could be readily identified as contained in the eigenvalues of the state matrix of the network, difficulty is seen to arise in the determination of zeros which can not so easily be calculated. A simple and efficient method is proposed reducing the determination of zeros to a standard eigenvalue problem.     

Influence of Measurement Parameters on Frequency Response Analysis Diagnosis of Oil‐Immersed Transformer

Appropriate monitoring and maintenance become important as an oil‐immersed transformer ages. Generally, dissolved gas analysis (DGA) is effective for the online diagnosis, and if an abnormality is detected, frequency response analysis (FRA) is effective for the offline diagnosis to localize the failed part. FRA diagnosis detects a slight change of waveforms; however, external factors may influence the results. Here, we discuss the influence of an insulating oil presence, tap position, and measurement lead wire length as possible parameters that influence the FRA characteristics. We confirmed that the measurement parameters examined here greatly influenced the FRA characteristics. In the actual diagnosis, it is important to remove these external parameters as much as possible, and keep a detailed record of the measurement parameters. © 2013 Wiley Periodicals, Inc. Electr Eng Jpn, 186(1): 18–25, 2014; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22313     

气体绝缘变电站内电压互感器高频传输函数模型的建立

为了计算气体绝缘变电站 (GIS)内由开关操作等对二次设备产生的传导干扰 ,必须建立电压互感器、电流互感器的高频模型 (f≥ 10MHz) ,提出了通过拟和TV/TA传输函数的幅度平方函数得到该传输函数的新方法 ,并建立了某GIS电站内 170kV感应式TV从 1MHz到 6 0MHz高频传输函数模型。拟和方法采用了运算速度快、拟和结果准确、稳定的矢量匹配法     

变压器频率响应法测试结果的影响因素分析及改善

目前采用频率响应法诊断变压器绕组变形的应用相当广泛,但是在实际测量中,其测试结果会受到诸多因素的影响而失真,若不能准确识别这些影响因素,测试结果的可比性将大大降低,从而给测试结果的分析、判断带来困难甚至错误。笔者结合频率响应法检测技术在天水电网的应用情况,总结了现场由于各种影响因素造成的绕组频率响应曲线异常的实例并将其逐一归类,为今后判断变压器绕组变形提供依据。     

基于端口频域特性的水轮发电机转子绕组匝间短路故障诊断

包含抽蓄发电机在内的大型水轮发电机转子为具有多匝长绕组的显极式转子,传统的基于交流阻抗测量的绕组匝间短路故障诊断方法存在灵敏性和便捷性等方面的不足。基于多导体传输线理论建立了显极式转子绕组的端口频域特性模型,通过仿真分析提出了故障判别和定位方法。最后通过真机转子的故障模拟和测试对诊断方法的有效性进行了验证。仿真和试验结果表明,所提方法能够在无需断开磁极间电气连接的测量条件下实现绕组匝间短路故障的诊断和定位。     

变压器绕组的特快速暂态建模

为了研究陡波前过电压对变压器的影响,从短路导纳参数出发,提出了一种建立变压器绕组高频集中电路模型的方法.该方法首先由短路导纳参数计算绕组各匝的电压传递函数,并利用矢量匹配法对得到的电压传递函数进行有理函数逼近;其次,对得到的有理函数形式的传递函数利用多点Pade逼近进行阶数缩减,得到变压器绕组电压传递函数的降阶模型;最后,运用网络综合技术建立变压器绕组的高频电路模型.该电路模型仅由R、L、C和理想变压器构成,其模型参数可以根据电压传递函数的极点和留数非常方便地得出.通过对电路模型的仿真结果与实际测量结果进行比较,验证了本文方法的正确性.     

根据量测轨迹计算轨迹灵敏度的卷积法

轨迹灵敏度刻画系统中某一参数、初始条件发生微小变化时系统动态轨迹的变化程度。轨迹灵敏度已应用于参数辨识、动态安全分析等电力系统研究领域。直接由定义计算轨迹灵敏度通常依赖于数值积分的方法,不仅计算费时,模型和参数的误差会影响轨迹灵敏度的计算结果,而且不能充分揭示轨迹灵敏度的物理本质。文中提出一种基于量测轨迹的轨迹灵敏度计算方法,可以克服上述缺点。将时域响应轨迹变换到复频域后,根据轨迹在复频域上的分析性质,证明了轨迹灵敏度可以表示为系统的阶跃响应轨迹与脉冲响应轨迹的卷积或它们的线性组合。电力系统算例表明所提出的方法简捷、有效、可行。     

变压器绕组传递函数的拟合原理及绕组变形诊断应用

针对利用频响分析法检测变压器绕组变形的特点,即检测得到的牲量是绕组的频谱（传递函数）,提出了利用正交多项式拟合变压器绕组传递函数的原理和方法。该方法避免了用普通多项式拟合传递函数造成的弊病。利用正交伴随矩阵求取传递函数的零、极点,并根据零、极点的后通过实例证明该方法简单、快速、灵敏度高,比仅仅依靠频响曲线判断绕组变形有了大的提高。     

气体绝缘变电站内PT的特快速暂态仿真建模

为了计算气体绝缘变电站(简称GIS)内由开关操作等对二次设备产生的传导干扰，必须建立电压互感器(简称PT)、电流互感器(简称CT)的高频模型(≥10MHz)。为此，提出了建立PT高频电路模型的新方法。首先根据互感器输入、输出端口之间的实测频率响应，用矢量匹配法(Vectoi Fitting Method)采用有理函数拟合其频域传递函数；然后根据实际需要，对该传递函数进行降阶处理；最后，应用一种特定的RLC电路综合方法建立了该PT的电路模型。该方法具有简单、有效和通用的特点，对于任何形式、任何电压等级的互感器均可使用。     

Application of vector fitting to state equation representation oftransformers for simulation of electromagnetic transients

This paper presents an efficient methodology for transient modeling of power transformers based on measured or calculated frequency responses. The responses are approximated with rational functions using the method of vector fitting. The resulting model is dynamically stable since only negative poles are used, and input-output stability is assured by a novel adjusting procedure. The methodology is used to formulate two different transformer models: (1) a full phase domain model realized column-by-column, and (2) a model utilizing modal diagonalization. The application of the models is demonstrated for a 410 MVA generator step up transformer     

谐振接地配电网对地绝缘参数双端谐振测量新方法

为解决谐振接地配电网对地绝缘参数测量过程中电压互感器漏阻抗和中性点对地支路阻尼电阻导致的测量误差问题,提出了谐振接地配电网对地绝缘参数双端谐振测量新方法。采用双电压互感器,通过消弧线圈内部电压互感器或零序电压互感器向配电网注入变频恒流特征信号,并从另一电压互感器测量返回的特征频率电压信号,对含阻尼电阻的零序谐振回路进行等效变换,搜索准确的系统谐振频率,实现了系统对地电容和对地泄漏电导的精确测算。该测量方法的电流注入与电压测量单元共同直接作用于对地绝缘参数支路,从原理上消除了电压互感器漏阻抗和系统阻尼电阻的影响,大幅提升了对地绝缘参数测量精度。在PSCAD/EMTDC仿真环境及某变电站10 kV侧对提出的对地绝缘参数实时测量技术进行了仿真分析与现场实验验证。分析结果表明,该方法测量精度高,不影响配电网正常供电且参数测量过程安全快捷、操作简便。     

Dielectric response studies on insulating system of high voltage rotating machines

A significant method to characterize the electrical properties of materials and to evaluate the condition of the insulating systems is the dielectric response study which can be done in the time or frequency domain. The dielectric response measuring results can be affected by different parameters like measuring voltage, temperature, water content and aging condition of insulating system. In this work numerous measurements are presented, thus to understand, how the dielectric response measurement results at the insulating system of high voltage rotating machines can be affected by these parameters in the time and frequency domain. Because of the importance of the dielectric response application as a non-destructive diagnostic method the possibilities and limitations of this method to reflect the deterioration processes due to thermal and electrical stress were also investigated. In addition the possibility to transfer the measuring data from the time to frequency domain was investigated and the calculated and measured data were compared. For the test object actual stator bars were used that were manufactured with epoxy VPI technology.     

Interpretation of Soil Resistivity Measurements: Experience with the Model SOMIP

A method and a computer program for interpreting soil measurement data are presented. The method employs a statistical estimation of soil parameters from four pin or three pin measurements. The analysis provides (1) the best estimate of soil parameters, (2) the error of the parameters versus confidence level, (3) a pictorial view of how well the estimated soil model fits the measurements, and (4) the measurements which are not consistent (bad measurements). The methodology is applicable to data obtained with four or three pin method over a small or a large area. It performs best when applied to measurements taken at various locations of the area of interest. A computer program has been developed based on this methodology with the symbolic name SOMIP (SOil Measurements Interpretation Program). Implementation details are discussed in this paper. The performance of the methodology is compared with test model data. In addition, the experience gained in interpreting soil resistivity measurement with the program SOMIP is presented in this paper. Specifically, many sets of actual data, taken from four major utilities, has been analyzed and the results are presented and discussed.     

电磁脉冲孔耦合瞬态响应SEM极点提取

为了描述电磁脉冲孔耦合瞬态响应特征,基于奇点展开法(SEM)和矩阵束算法,将含有噪声的离散瞬态响应数据表示成矩阵的形式,并分解构造矩阵束,通过奇异值分解(SVD)和广义最小二乘法来进行参数估计,建立了提取电磁脉冲孔耦合瞬态响应极点及留数的模型,进行了仿真和重构实测响应波形.结果表明:模型所提取的参数完全可以描述响应的主要特征;噪声对留数影响较大,对极点的影响较小,因此在数值计算时,可保留有限个主要极点,忽略大量非主要极点,从而提高算法的效率,同时保证数值计算的精确度和稳定性.     

Time Response of the Frequency of Hydroelectric Generator Unit with Surge Tank Under Isolated Operation Based on Turbine Regulating Modes

Aiming at studying the regulation quality of isolated turbine regulating systems under load disturbance and different regulation modes, the complete mathematical model of a turbine regulating system under three regulation modes is established. Then, based on dominant poles and null points, the method of order reduction for a high-order system of time response of the frequency is proposed. By this method, the complete high-order systems are solved and the regulation quality for time response of the frequency is studied. The results indicate that (1) the tail wave, which is the main body of time response of the frequency and the principal factor that determines the regulation quality, is mainly determined by the dominant poles; (2) for the three regulation modes, by deleting the high-order terms, the three equivalent overall transfer functions are fourth order, third order, and third order, respectively, and can be solved; (3) the analytical fluctuation equations of time response of the frequency solved from low-order equivalent overall transfer functions accurately simulate the fluctuation characteristics of time response; and (4) based on damped vibrations decomposed from analytical fluctuation equations, the regulation qualities of three regulation modes are analyzed.     

基于虚拟仪器技术的民机动态信号分析仪

基于虚拟仪器技术,利用LabVIEW软件开发一套应用于民用飞机振动测试分析的动态信号分析仪.通过对该仪器的控制和参数设置,实现自定义信号模拟输出和数据的实时采集、分析处理与显示.具有时、频域分析和通过3种方式获取系统频率响应函数等功能,该虚拟仪器界面美观、操作方便、层次清晰、功能强大,能够基本满足民机振动测试分析的需要...     

Robust current control for boost PFC converters from a sliding mode viewpoint

In this paper, we propose a methodology to derive a pulse‐width modulation (PWM) control for the inner current loop of the boost power factor correction (PFC) converter. The methodology is based on the general sliding mode control theory. It leads to a robust current control that achieves accurate input current tracking under all practical conditions. The design of the control parameters is also presented, which is based on the existence condition and the frequency response analysis. The derived control can be implemented in analog circuitries as an application‐specific controller or as an add‐on feedforward control embedded in standard PFC controller circuits. Copyright © 2010 John Wiley & Sons, Ltd.