Dielectric characterization of power transformer oils as a diagnostic life prediction method

The monitoring of the complex permittivity of transformer oils as a function of frequency and temperature provides information concerning the state of the insulation. In this work, it has been investigated as a quality control method, providing service life estimations of power transformations. The formation of databases recording polarization effects in a wide frequency and temperature range may be used effectively as a working tool for service engineers. Reliable insulation monitoring reduces accidents in aged HV transformers, some of which have been in operation since the 1960s. These transformers always impose an environmental threat because of possible accidental leaks or fires, especially when containing traces of PCBs.     

频响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.     

影响变压器频率响应测试结果的因素分析

为消除电网中变压器绕组变形引起的事故隐患，章根据频率响应法在嘉兴电网中应用的实际情况，在4年多的时间内对所辖的500kV主变压器1台／次、220kV主变压器28台／次，110kV主变压器156台／次进行了多次现场测试，研究得出了在现场应用该方法测试对变压器绕组变形的频响曲线几种影响因素，同时，提出利用频响法测绕组变形的注意要点。     

一例出口的长输电线路末端的电力变压器设计

设计了一种出口的长输电线路末端的电力变压器,分析了由于上级母线和输电线路产生的阻抗压降引起的变压器电源电压变动时的计算方法,及变压器一次侧调压方式和电源波动范围、频率的关系。指出变压器设计过程中要针对具体的项目进行综合分析,合理选择变压器参数,改进变压器结构。     

工频通信信号在我国配电网中的传输特性

针对我国配电网与美国配电网接地方式的不同,分析了配电变压器对工频信号传输过程的影响,指出我国中压配电网中性点不接地方式对工频通信信号有明显的衰减作用,并与配电变压器的连接组别相关。最后对不同的信号衰减情况提出了改进通信效果的建议,包括增大信号调制幅度,改进信号检测技术,对Yyn-0型配电变压器通过减少装置内部电感来解决上行信号调制幅度不足的问题等。     

Determination of phase angle and amplitude error of voltage and current transformers up to some 100 Hz for loss measurements on power transformers

Contents  For the load loss measurement of power transformers, current and voltage transformers with usually extremely low errors of phase angle and amplitude are used. However, even small errors of the measuring transformers may result in an error in the measured load loss. Therefore, national and international standards allow the correction of the measured value by the amount caused by phase angle and amplitude error of the measuring equipment [2–4]. The determination of the errors of phase angle and amplitude of measuring transformers is carried out on the basis of calibrated standard measuring transformers which are traceable to national standard equipment at rated frequency, e.g. at 50 and 60 Hz. For some applications – e.g. the load loss measurement of HVDC power transformers according to the draft of IEC standard 61378-2 [1] – a load loss measurement at frequencies other than rated frequency is required. For that, the errors of phase angle and amplitude of the measuring transformers must be known. This paper describes a method how to determine the phase angle and amplitude errors of the measuring transformers at arbitrary frequencies on the basis of the calibrated error values at rated frequency. Received: 9 August 2000     

An improved nonlinear thermal model for MV/LV prefabricated oil-immersed power transformer substations

The largest part of the investments of transmission and distribution systems is due to transformers used in changing the voltage level. The operating life of transformers is important due to their considerable economic impact on the power systems. To ensure the economical operation and secured service it is important to have knowledge about the insulation condition, operating life, and loading capacitance of transformer. The most important parameter in transformers life expectancy is the insulation temperature level, which accelerates the rate of aging of the insulation. The modeling of the energy balance and heat transfer of transformer is a major task in transformers thermal modeling. The aim of this paper is to present improved thermal models for transformers loaded at prefabricated MV/LV transformer substations and outdoor situations. The top-oil temperature is studied both for indoor and outdoor transformers and the thermal models proposed for them are compared. Since the thermal transfer is different for indoor and outdoor transformers considering their operating conditions, their thermal models differ from each other. The proposed thermal models are verified by the results obtained from the experiments carried out on typical indoor 30 kV/0.4 kV transformer stations at different operating conditions.     

A study on hot spot detection possibility in simulated oil‐filled‐type transformer tank by using ultrasonic methods

Failure of oil‐filled‐type (OFT) power transformers usually results in very big losses comprising the loss of the transformer itself as well as production loss in industry. Most of the energy lost in OFT transformers, induced by faults, will become heat at a location close to the fault, which then becomes a hot spot. The detection of hot spots in OFT transformers can be an effective way for transformer fault location and diagnosis. As the OFT transformer enclosure is completely sealed and is opaque, to date there is no effective way to find out hot spots in them. It is known that ultrasonic energy can be transmitted into the sealed transformer enclosure which is filled with the fluid, and ultrasonic waves can be affected by the temperature of the materials they propagate through; so the ultrasonic method can be a possible method for hot spot detection. In this paper, we describe a study on the possibility of developing a method to detect hot spots in an environment filled with a fluid, simulating a transformer. Trails using a different times‐of‐flight (TOFs) evaluation techniques and attenuation measurement of the ultrasonic energy propagated were carried out, which showed encouraging results for locating the hot spot as well as measuring the hot spot temperature in fluids; we also discuss the possibility of applying these results to the diagnosis of OFT transformers eventually. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

电容型设备绝缘在线监测现场应用实践

介绍电容型设备绝缘在线监测的测量原理、电流和电压采样方式的选择原则,讨论了2组不同运行年限的线路电流互感器介质损耗在1周内随温度、湿度的变化情况,指出了电流互感器介质损耗变化受温度和湿度的影响具有个体差异性。     

油浸变压器绝缘受潮的介质响应诊断技术研究

现场条件下准确诊断变压器的受潮程度一直是难点,通过对变压器及油纸模型的介质响应测试,分析温度及水分对介质响应的影响.结果显示温度升高主要使介质响应曲线在频率轴方向向高频方向移动,而水分增加主要使介质响应曲线在介质损耗轴方向向上平移.复电容虚部极小值大小随温度变化不明显,但却随着水分的增加呈指数形式显著增加,这一规律,为准确判断变压器的受潮程度提供了一种依据.     

Analysis of Temperature Distribution in Cast-resin Dry-type Transformers

Non-flammable characteristic of dry-type cast- resin transformers make them suitable for residential and hospital usages. However, because of resin’s property, thermal behavior of these transformers is undesirable, so it is important to analyze their thermal behavior. Temperature distribution of cast-resin transformers is mathematically modeled in this paper. The solution of the model was carried out successfully by finite difference method. In order to validate the model, the simulation results were compared with the experimental data measured from an 800 kVA transformer. Finally, the influences of some construction parameters and environmental conditions on temperature distribution of cast-resin transformers were discussed.     

A Comparison of the Impregnation of Cellulose Insulation by Ester and Mineral oil

Ester oils have been successfully used in distribution transformers for many years as satisfactory substitutes for mineral oil. In high voltage transformers however their application has been much slower partly due to the fact that the high viscosity of ester oil and hence uncertainties in efficient impregnation of cellulose insulation. In this paper the characteristics of the impregnation of cellulose insulation by ester oils are assessed and compared with mineral oil. Studies are carried out on thick laminated pressboard blocks, typical of support insulation structures in high voltage transformers. The degree of oil impregnation with time at various temperatures is examined. It is shown that the factors governing the impregnation processes with ester and mineral oils are very similar, i.e. mainly viscosities and surface tensions, and if a higher impregnation temperature is used for ester oils the same degree of oil impregnation can be achieved as with mineral oils.     

温度对典型光学电压互感器误差特性影响的研究

光学电压互感器容易受到温度影响,其误差特性是实际工程应用关注的焦点。文中首先介绍了几种典型原理的光学电压互感器,建立了光学电压互感器试验平台及试验方案,并针对已经实用化的2种原理的光学电压互感器开展了温度影响试验,提出了电容分压原理的光学电压互感器温度性能较好的观点。     

考虑故障阻抗与多级变压器影响的电压凹陷评估

综合考虑了故障阻抗的随机性和不同绕组联接方式的多级变压器对凹陷评估的影响。建立了故障阻抗的随机分布模型和多级变压器的等效移相矩阵,对考虑2个方面影响因素后的电压凹陷幅值与频次评估的数学模型、算法和步骤进行了详细研究。对简单9节点系统和IEEE30节点系统进行了仿真分析,结果证明,变压器绕组联接方式对电压凹陷幅值和频次均有影响,故障阻抗对电压凹陷幅值有明显影响,与现有评估方法进行比较,评估结果准确,原理简单,适用于任意规模与结构形式的电网。     

基于小波理论的电力变压器振动信号特征研究

通过监测电力变压器的器身振动信号预估变压器机械故障的振动法的关键在于如何从振动信号中提取有效特征。为有效诊断铁心和绕组的机械状态,利用小波变换对变压器振动信号进行时域与频域综合分析,提出基于频段—能量分布的变压器铁心和绕组机械故障诊断新方法。试验结果表明,小波变换能够有效地提取振动信号的特征,得到实时振动信号各频段上的能量分布状态,据此可有效在线诊断变压器机械故障。     

电子式电压互感器传感器设计

为适应配电自动化和数字变电站的需要,研制出应用于电子式电压互感器的传感器.该互感器以电容分压器为基础,其中电容分压器由金属导电棒、双面柔性电路板和聚四氟乙烯组成的等效电容构成.用柔性电路板可将前级放大电路放在传感器的内部,以提高系统的信噪比和测量精度.采用介电性能与温度、频率无关的聚四氟乙烯作为绝缘材料,可有效地减少温度和频率对测量的影响.并增加了系统的稳定性.最后,Matlab仿真证明该传感器具有良好的暂态响应;多次试验结果表明由该传感器组成的电子式电压互感器样机测量精度为0.2级.     

高温超导变压器

高温超导变压器与常规变压器相比 ,具有体积小、重量轻、效率高、无火灾隐患、不污染环境和限制短路电流改善系统动态稳定性等诸多优点。阐述了欧洲、美国及日本等国家的高温超导变压器的研究现状、基本特点、优越性及研究中存在的技术问题等。并且讨论了高温超导变压器的设计原则和将来其投入电力系统运行时所需要进一步考虑的问题     

Background information on high temperature insulation forliquid-immersed power transformers

The availability of insulation materials having a higher temperature rating than cellulose has led to the design of high temperature power transformers for specialized applications where size and weight are important considerations. Such applications include traction transformers, mobile transformers, and power transformers with special loading requirements. Even though such equipment has been in use for many years, there are presently no standards which address high temperature materials in liquid-immersed transformers. Recognizing this deficiency, the IEEE Transformers Committee has established a Working Group to investigate what standards or guides could be formulated. As a first step, the Working Group has prepared this “state-of-the-art” paper to document background information on the materials and their application. It is hoped that discussion of this paper will help to establish future directions for standards     

Pattern classification of impulse faults in transformers by wavelet analysis

One of the tests carried out on a transformer after assembly is the lightning impulse test, for assessment of the integrity of its winding insulation. In the case of a fault, it has been well established that the pattern of the fault currents contains a typical signature of the nature and location of the insulation failure involved. This paper describes a new approach using the 'wavelet transforms' to classify the patterns inherent in different fault currents. Whereas conventional frequency-response analysis based techniques fail to identify the time-localization of a particular frequency component in a time-dependent signal, the wavelets are not only localized in frequency, but also in time. The 'time-frequency localization' feature of wavelet transform is employed for pattern classification of impulse fault currents of transformers. Results for simulated models of 3 5 and 7 MVA transformers are presented to illustrate the ability of this approach to classify insulation failures.     

变压器局放特高频检测中检测频率和带宽的影响

变压器局部放电特高频检测中,检测频率和带宽的选取对于放电信号的提取,进而对放电的标定及局部放电模式识别特征的保留具有决定作用.本文在实验室中建立了局部放电特高频检测系统和变压器典型局放模拟系统,对特高频检测中检测频率和带宽的选取原则进行了实验研究.实验结果表明,检测频率应选择局部放电特高频分量丰富且噪声小的频带,滤波器的带宽应在不引入干扰的前提下尽量选用较宽的带宽.