基于模糊和证据理论的变压器本体绝缘状态评估方法

对电力设备运行状态进行准确可靠的评估是实施电力系统状态检修的前提和基础。以500 kV油浸式变压器为研究对象,构建了基于模糊和证据理论的变压器本体状态评估模型。选取预防性试验中具有代表性的参数为状态评估的指标,参考评价指标的出厂值和越限值进行指标归一化,利用模糊评判方法确定各个指标相对于不同状态评估等级的隶属度。将这些指标分为油中溶解气体、油化试验和电气试验三个子证据体,利用证据理论对三个子证据体进行信息合成,进而对变压器本体的运行状态进行评估。通过对某台500 kV变压器数据的实例分析验证了该评估模型应用于变压器本体状态评估中的有效性。该评估模型思路清晰,不需要大量的历史数据,为变压器状态评估提供了一种新方法。     

基于模糊层次分析法的变压器状态评估

变压器状态评估是一个系统的过程,选取合适的方法能够快速地对其运行状态进行准确的评价。综合变压器的特点提出了一种基于模糊层次分析法的变压器状态评估方法。该方法在合理运用模糊层次分析法的同时克服了主观因素的缺陷,通过历史统计数据确定模糊判断矩阵,并通过模糊层次分析法计算权重,采集现场状态量数据对各层次状态评分加权求和,最终确定变压器整体健康状态。此方法同时考虑现场实测数据和历史统计数据,计算结果准确,过程清晰。代入实际数据后,计算结果表明该方法能够准确评估变压器运行健康状态,若变压器处于非正常状态,则通过各故障类型打分分析判断具体异常原因。所提方法在进行变压器状态评估时具有广阔的应用前景。     

基于多维正态云模型的电力变压器状态评估

针对变压器状态评估中对于定量信息评定的模糊性和随机性问题,采用多维正态云模型进行变压器状态评估,其中采用的核空间多维云算法可以有效避免各个指标之间的权重难以权衡的问题。通过对变压器运行数据进行正态云拓展;利用正态云发生器不断产生云滴;根据各个指标给定的区间范围拓展为评级标尺云,以数据云所产生的云滴作为输入,采用多维云算法计算出该变压器的运行状态。以某台变压器运行信息作为分析对象,通过算例分析验证了该方法的有效性,且证明了方法具有简洁、高效和可靠等特点。     

Peak-switching currents of power transformers

The switching conditions of nonloaded transformers have been investigated to understand the effect of current inrushes and limitations by considering the connecting circuit of the windings, magnetization performances, contact parameters, type of switcher drive, and the value and sign of residual magnetization. The peak-switching currents have been calculated, simulated, and measured and the results have been compared. The obtained results make it possible to increase the power efficiency of the facility by decreasing the losses and maintainign the quality factor of electric power in transient modes.     

Unusual cases of gassing in transformers in service

This paper presents some unusual cases of gassing in transformers in service without an actual fault. These cases reveal that hydrogen production caused by stray gassing may be due to strongly hydro-treated oils, but is also very strongly influenced by transformer materials. Stray gassing with overproduction of saturated hydrocarbons with no production of hydrogen and no increased rates of hydrogen, ethylene, and other fault gases has probably always existed and is possibly related to oxidation. The overproportional development of methane and especially ethane proceeds in the first years of service and reaches a plateau after considerable consumption of oxygen. Possibly, this process is also catalytically triggered by transformer materials. Catalytic phenomena and stray gassing can be distinguished from a transformer fault through regular checks not only of the absolute DGA values but also the rates of gas increases.     

基于关联规则与变权重系数的变压器状态综合评估方法

为了提高变压器诊断的准确性和适应设备检修的发展趋势,克服传统智能算法的局限性,提出一种基于关联规则和变权重系数的变压器状态综合评估的方法。根据试验和监测数据建立评估体系,通过9种综合故障和24种单项故障状态量,利用关联规则分别计算置信度和变权重系数,结合变压器的运行状态与检修对照关系,诊断变压器的整体指标。实验结果表明该方法准确率达到91%,能够准确评估电力变压器的健康状态。该方法可为运维人员做设备检修提供科学指导方案,也为其他高压设备的状态评估提供参考和借鉴。     

基于云相似度与证据融合的电力变压器状态评价方法

针对电力变压器状态评价过程中存在的不确定性,提出一种基于云相似度和证据融合的电力变压器状态评价方法。首先,考虑到各指标在状态等级边界处的随机性与模糊性问题,采用云模型来建立状态评价的基本框架。其次,为兼顾状态等级划分的严明性和模糊性,采用改进的云熵优化算法确定云模型的熵值。然后,考虑到指标数据本身的不确定性,利用正向云发生器和云合成算法生成各试验项目待识别云和标尺云,并采用模糊贴近度计算二者间的相似度作为证据源的基本概率分配。最后,采用考虑证据可信度和不确定度的冲突证据修正方法修正证据源,并融合不同证据以判断电力变压器的最终状态。经实例验证,相较于传统方法,所提方法能够有效处理状态评价过程中的不确定性,评价结果符合电力变压器的真实情况,对电力设备状态评价有一定参考价值。     

Characterization of static electrification in power transformers

Static electrification due to oil now causes many field failures of large forced-oil cooled power transformers. Also, in practice under normal operating conditions, the oil volume in these power transformers is reduced due to the internal heat generated (from the energized windings) which accelerates the chemical processes occurring inside. To complete filling of the oil tanks of such transformers, either new oil of the same or different type is used. Laboratory analogs of these transformers; namely a closed and an open cycle, have been used for investigating this phenomenon. Such tests have been performed upon different types of fresh and aged oils and oil mixtures to measure the electrification current. Investigations of the effect of oil temperature, oil velocity, frequency and type of the applied voltage, type of the solid-phase material, and the length of the oil gap are introduced. Also, a 200 kVA, 3.3 kV/380 V distribution power transformer is used where the oil is forced and heated externally to examine and demonstrate this phenomenon for unenergized and energized cases and for both fresh and aged oils     

电子式互感器评述

概述了互感器传感准确化、传输光纤化和输出数字化的基本发展趋势.以IEC标准为基础,讨论了电子式互感器的结构体系和电子式互感器与数字变电站的关系.评述了电子式互感器的各种实用化的传感方法.介绍了POSS-OCT光学电流互感器实用化的基本情况.     

Sensitivity of UHF PD measurements in power transformers

The reliability of electrical energy networks depends on the quality and availability of electrical equipment like power transformers. Local failures inside their insulation may lead to catastrophic breakdowns and might cause high outage and penalty costs. To prevent these destructive events power transformers are e.g. tested for partial discharge (PD) activity before commissioning and currently also during service. The current work deals with the electromagnetic PD detection method, also known as UHF method. The disadvantage of the UHF method is still the missing possibility for a calibration or at least a verification of the sensitivity. The so-called Sensitivity Check might show in future a relation between unconventionally measured UHF quantities to the apparent charge level in pico Coulomb. An important aspect is the attenuation of UHF signals within power transformers which is investigated in this paper.     

基于模糊综合评估模型与信息融合的电力变压器 状态评估方法

针对电力变压器状态评估中存在多特征指标和多故障类型问题,提出一种基于模糊综合评估模型和皮尔逊相关系数的改进D-S证据理论的变压器状态评估方法。建立了变压器状态评估体系,引入层次分析方法和改进的三角梯形隶属函数确定特征指标的基本概率。基于皮尔逊相关系数的改进D-S证据理论融合不同特征指标以评判变压器综合状态评估。经过实例分析,该方法的评价结果与变压器实际运行状态一致,其准确率达到95.83%,验证了该方法的合理性和可行性。该方法对变压器状态评估具有一定的参考价值。     

PPS electrical properties for power transformers

In order to find a material that can be used as wrapped insulating film in the power transformer industry, we have tested polyphenylene sulfone which is film characterized by a high thermal resistance, a high chemical resistance and an outstanding mechanical strength. The thermal degradation study is of major importance in this application, so thermal aging test in the presence of silicone oil at 160°C was carried out in reactor. Dielectric breakdown, partial discharges, conductivity, permittivity and dielectric loss measurement were studied in the investigation     

Large transformers for power electronic loads

The transformers described here are in the multi-megawatt range. They are rapidly becoming more important and have characteristics and features that are different in many ways from those of normal power transformers. Information about them has been incomplete, scattered and hard to find in the literature. Harmonics are of prime importance in these transformers. Their appearance and suppression are explained with an emphasis on making it easy to understand. Different winding arrangements are presented and their characteristics explained. Cores with gaps to limit inrush currents are also discussed     

Multiturn high-frequency coaxial winding power transformers

Previous papers on coaxial winding transformers have focused on designs that use a copper tube to form a single-turn outer winding, and litz wire for a multiple-turn inner winding. In high-power applications, the increased resistance of a solid outer winding due to skin effects can be a limiting factor in achieving good performance, especially at frequencies above several hundred kilohertz. A single-turn outer winding leads to large core cross section areas at lower frequencies and the turns ratio is limited to a ratio of n:1, where n is an integer. This paper demonstrates several methods for achieving multiturn outer windings to improve design flexibility for the coaxial winding power transformer. Experimental measurements on transformers that have multiturn outer windings are included to confirm analytical results and demonstrate the modified designs     

On real-time assessment of post-emergency condition existence in complex electric power systems

This paper presents two effective numerical criteria of estimating post-emergency operating conditions’ non-existence in complicated electric power systems. These criteria are based on mathematic and programming tools of the regularized quadratic descent method and the regularized two-parameter minimization method. The proposed criteria can be effectively applied in calculations of real-time electric operating conditions.     

电力变压器的安装及缺陷处理

叙述了电力变压器安装的一般步骤,包括安装前的准备工作、安装程序和安装过程中的试验项目。根据现场经验,对安装过程中可能出现的问题进行了分析,并提出了解决方案,给出了安装过程中变压器缺陷的处理方法。     

Effects of direct currents in power transformers Part II. Simplified calculations for large transformers

In a previous paper, a general theoretical method was developed to calculate the effects of direct current circulating in single-phase transformers of any rating. The method is now applied to HV and large distribution transformers. Simplified calculation formulae are deduced to provide magnetizing current and voltage along with their harmonic contents. The effects of DC saturation and over-excitation are compared. A method of core saturation and magnetizing current calculation is presented for the case of a rectified load or a DC source between two transformers.     

Electromagnetic processes in power transformers with vector control

One possible circuit of a power transformer with vector control is considered. Initial statements of the electromagnetic analysis of transformers are given. An algorithm for determining the voltage and current time dependences, as well as characteristics ones, is described. The dependences between the power transformer characteristics with vector control and the control parameters are shown by the example of the transformer with a nominal power of 16 MV A and nominal supply voltage of 110 kV. The conclusion is drawn that minimum power losses are present at a certain combination of control parameters. The time dependences of current and voltage power keys involved in the transformer of active converters, which result from the mathematical simulation in MATLAB and Simulink, are presented. The effectiveness of the proposed model is evaluated.     

On the use of silicone liquids in power transformers

The insulation and basic physical characteristics of insulation liquids MIDEL 7131 (ester) and SOFEKSIL–TSZh (silicone liquid) are considered. It is shown that the SOFEKSIL–TSZh liquid is characterized by a higher flash point, which is important for providing the fire safety of high-voltage electrical equipment. Taking into account that contradictory data on the electrical strength of silicone liquids are contradictory, studies on the electric strength of the SOFEKSIL–TSZh liquid and transformer oil have been performed for sharply nonuniform fields at an impulse voltage of 1.2/50 μs for both polarities. It is shown that the electric strength of the SOFEKSIL–TSZh liquid is similar to the electric strength of GK transformer oil and MIDEL 7131 liquid. It is concluded that the SOFEKSIL–TSZh liquid can be used in power transformers in the case of increased requirements for fire safety.