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.     

Design of the winding–bushing interconnections in large power transformers

The paper presents the improvement in design of the conductor connecting the windings and bushings in oil power transformers. This is a sensitive part of large transformers and there is a need to optimise its manufacturing time and costs. The thermal problem of the heating of this conductor with increased insulation thickness on a part of it is treated using a non-linear two-dimensional thermal model. The experiments performed made determining of some problematic parameters (heat resistance of oil-paper insulation and the paper to oil convection heat transfer coefficient) of the thermal model feasible. The results obtained are of practical interest in the design practice of interconnections, but also affect the important parameters of heat transfer by devices with oil immersed paper insulation.     

变压器绕组变形的扫频短路阻抗法研究

针对变压器因绕组变形而产生故障问题,分析了现有短路阻抗法和频响法检测绕组变形手段的特点和不足,研究了扫频短路阻抗法的基本原理和测试接线方式,在模型变压器上进行了绕组层间短路、绕组匝间短路等不同情况的试验测试,初步验证了该方法的有效性。以某220 kV变压器为测试对象,采用扫频短路阻抗法进行了变电站现场测试工作。该方法测试结果能够提供更多的测量参量,为绕组变形的研判提供了更多的参考依据,是一种很有价值的变压器绕组变形测试方法。     

虚拟仪器在变压器绕组变形故障诊断中的应用

介绍了变压器绕组变形测试系统的硬件选择、软件设计、系统的实现及应用情况。     

一种配电变压器绕组变形故障的在线监测新方法

针对电网对变压器绕组健康状态在线监测的需求,提出了一种新的变压器绕组变形故障在线监测方法。通过在线测量两种不同负荷下一次侧和二次侧的电压电流,计算出变压器的短路电抗值,进而反映变压器绕组变形情况。此方法的突出优势在于无需空载调零,不受激磁电流变化影响,不受运行中配电变压器一次侧电压随电网电压波动的影响且精度很高。将所提方法应用于不同容量的配电变压器,仿真结果显示该方法能够精确有效地在线测量正常变压器和有不同程度变形故障的变压器的短路电抗值,从而实现配电变压器绕组变形故障的在线监测。依据本方法的特点,设计了实现短路电抗在线监测所必需的数据采集模块和分析模块。     

变压器绕组变形现场测试中应注意的问题

总结了变压器绕组变形测试中常遇到的问题,提出了处理建议和基本测试原则,并给出了数据分析处理方法.     

Method for determining optimal power transformers exploitation strategy

The paper suggests a procedure for determining an optimal combination of activities and measures to minimize the expected total costs during the planned exploitation period of power transformers.Combinations of different types of preventive maintenance, spare parts keeping and installation of condition monitoring systems of power transformer individual components are taken into consideration. Power transformer is a complex system, consisting of six components (functional parts). It is assumed that each component has two independent, competing failure modes: a wear-out failure mode, modeled by two-parameter Weibull distribution, and a chance failure mode, characterized by an exponential distribution.The superposition of failures and planned maintenance are taken into account in the analysis of some forms of preventive maintenance.The application of the method suggested and the benefits it provides are demonstrated for one transformer station (TS) 110/10 kV/kV with 2 × 31 500 kVA-110 kV Star-10 kV Delta transformers in case of radial supplying of customers as well as in case when outage of one power transformer does not affect the power supply to customers.     

图形学在频响数据诊断变压器绕组变形中的应用

为提高频率响应分析法诊断变压器绕组变形的诊断效果,根据变压器绕组频率响应分析法的数据特点,将数学形态学方法引入变压器绕组故障诊断,以图形表示频率响应曲线间的差异,用数学形态学方法处理这些图形得到关键图块,计算关键图块的形态参数,根据关键图块的数量和形态参数判断变压器绕组状态,为通过频率响应特性试验判断变压器绕组变形提供了一种新的数据分析方法.     

A probabilistic feature to determine type and extent of winding mechanical defects in power transformers

Frequency response analysis (FRA) is a widely-used method to detect axial displacement (AD) and radial deformation (RD) in windings of power transformers, because of its high sensitivity to small amount of mechanical defects. Interpretation of frequency response curves has been the most intricate problem of FRA method. To solve it, different numerical indices have been introduced by researchers to evaluate the frequency response of power transformers, but (1) the researchers have not discussed on genesis origin of the proposed indices and (2) most of these indices can not present a regular and linear behavior. In this paper, a probabilistic feature has been utilized to demonstrate how an efficient index originates, to diagnosis axial displacement and radial deformation in windings of power transformers. The resulted index presents a nearly linear mapping between frequency response curves and their related defect extent. To verify usefulness of this index, it has been applied to several sets of measured frequency response curves. It is illustrated that the extracted index is able to determine extent of the defects. To discriminate between axial displacement and radial deformation, local behavior of TF curves has been used.     

A simple method for calculating winding temperature gradient in power transformers

This paper presents a new method for calculating winding temperature gradient in large power transformers. A general formulation of the problem is made using the electrical analogy. An expression for the thermal resistance of the solid insulation is found using analytical methods. Expressions for the thermal resistance of the oil boundary layer for natural and directed oil flow are then found through correlation of test results from actual transformers. A comparison of the results of the new method and previous methods is presented. The new method is found to be a significant improvement.     

Temperature distribution in foil winding for ventilated dry-type power transformers

Predicting temperatures of transformers is important in order to prevent the deterioration of electrical insulation since the life of the transformers corresponds with that of the insulation. Reports of thermal behavior of ventilated dry-type transformers are rare in the literature. In particular, foil winding has received little attention despite their wide usage in practice. In this study, a thermal model for foil winding was proposed and temperature distributions were determined by the finite element method (FEM). In order to cope with the non-uniformity of the heat fluxes in the foil winding due to induced currents, different convection coefficients and varying air temperature along the vertical height of the foil winding were suggested and applied to the thermal model. The thermal model was solved by coupling it with the electromagnetic model to calculate the non-uniform power losses. The model was applied to a ventilated dry-type power transformer rated at 2000 kVA. Experimental temperatures were measured with thermocouples, and used to verify the finite element results. They showed reasonable agreement and will provide a useful tool for transformer engineers.     

变压器绕组模拟变形的对比研究

针对模拟状态下变压器绕组的变形，应用频率响应分析法和漏电感测量法进行了对比研究，并进行了测量分析。     

基于电气量特征的变压器绕组变形监测技术现状与展望

介绍电力变压器绕组变形产生的原因及表现形式,着重分析和总结现有的基于电气量特征的电力变压器绕组变形传统的离线检测技术和在线监测理论的特点及应用,并分析现有方法存在的主要问题和原因。结合变压器绕组变形与漏电感参数的变化关系,指出变压器绕组漏电感参数的准确实时计算将成为绕组变形监测,尤其是从离线到在线监测技术发展的关键问题。     

Application of a general regression neural network for health index calculation of power transformers

A power transformer is one of the most important components in a transmission network. To assess the overall condition of this valuable asset, health index calculations are recently gaining more attention from the utility companies that operate networks. Only limited research has been conducted on health index calculations of transformers. Most of the past approaches are based on the linear combination of weighted scores of measurements following the industry standards such as IEEE, IEC and CIGRE. A few previous methods based on artificial intelligence and statistical approaches such as fuzzy logic, multivariate analysis and binary logistic regression have been published in recent years. In this paper, a General Regression Neural Network (GRNN) which has a nice nonlinear property and can work with measurements without quantization has been evaluated. The GRNN allows multi-dimensional measurements to be combined through an optimal weighting and scoring system to compute a quantitative health index of power transformers. The weighting of each test was assigned based on a smoothly interpolated continuous function. The efficacy of the model has been validated against expert classifications and data sets published in the literature. The comparative results demonstrate that, the proposed method is reliable and very effective for condition assessment of transformers through an automated health index calculation.     

发电机、变压器类电力设备的状态监测与故障诊断

针对发电机、变压器类电力设备普遍采用的预防性定期检修方式所存在的弊端,分析了发展状态监测和故障诊断技术的意义,并对该技术在国内外的发展现状和存在问题进行了介绍。最后指出,发电机、变压器类电力设备的状态监测和故障诊断技术,可以迅速、连续地反映设备的运行状态,预示运行设备存在的潜伏性故障,是保障电力设备安全经济运行的有力措施,应大力推广。     

Maximum insulation stresses under transient voltages in the HVbarrel-type winding of distribution and power transformers

Analytical as well as experimental results are presented for voltages developed in HV (high-voltage) windings of dry-tyre power and distribution transformers when subjected to surge transients. Although the existence of this phenomenon has been known for years, it has not always been taken into consideration in the calculation of insulation stresses. The possibility of accurate prediction of the developed voltages is demonstrated     

运行中的SF6变压器的气体监督检测

SF6气体绝缘变压器在我国电力系统中的应用越来越广泛,建立运行中的气体分析的有效检测手段和监督依据,对此类电气设备进行监督管理显得尤其重要。为此,根据深圳供电分公司SF6变压器投运七年来的运行情况和监督检测方面所积累的经验,结合厂家的监督标准,提出了SF6变压器气体监督检测方面的建议,为SF6气体绝缘变压器的安全运行和监督提供参考。     

短路阻抗法在变压器绕阻变形测试中的应用

短路阻抗是变压器的一个重要特性参数,决定了变压器在系统短路时短路电流的大小及变压器内部的电动力的大小。在变压器受短路冲击时,通过短路阻抗试验及绕组变形试验可检测出该受冲击变压器是否受变形。当变压器已发生变形时可通过测试变压器的单相漏抗来判断冲击变压器绕组发生变形相。     

电力变压器局部放电检测技术的现状和发展

本文概述了电力变压器局部放电检测技术的研究现状,着重论述了近几年发展起来的数学化测量和超高频（UHF）检测,并对电力变压器局部放电检测技术的发展前景作了探讨。     

频率响应法在诊断绕组变形中的应用

介绍了应用频率响应分析法检测变压器绕组变形的两个实例。指出在检测中通过对前后频谱曲线的分析,能准确有效地发现变压器内部电气及机械事故隐患,对于变压器及电网的安全运行,有着重要意义。但频率响应分析法不一定能够有效反映出变压器绕组变性发生单一扭动变形这类故障,绕组变形的诊断仍需使用多种试验手段综合分析和判断。