潜油泵故障产生的故障气体分析

变压器潜油泵是大型变压器强油冷却系统的关键附属设备,由于潜油泵故障发生放电,从而使因故障产生的乙炔气体进入到变压器油中,严重威胁变压器安全稳定运行。文章对潜油泵故障引起变压器油色谱异常进行了分析。     

Development and calibration of a streaming electrification modelfor a cellulose duct

Streaming electrification occurs in large power transformers where insulating oil circulated for cooling purposes acts to separate charge from the interfacial double layer present on a multitude of cellulose insulation surfaces. In this paper, the electrification phenomenon is addressed from a microscopic viewpoint. An empirically calibrated analytical model is provided for calculating the amount of charge separated in a core-form transformer duct. The model incorporates a boundary layer approach in approximating the wall charge distribution which provides a critical length scale for the analysis. This length scale is used to specify the appropriate model for charge development under turbulent flow conditions. The duct model considers both laminar and turbulent flows subject to ac electric fields and varying temperature. This concept forms the elemental building block of a network-based methodology for examining electrification in a complete transformer geometry     

大型换流变压器油流带电问题的分析

油流带电可能破坏换流变压器的油道绝缘性能，成为威胁超高压变压器甚至影响电网安全、稳定运行的重要因素之一，在特殊的绝缘结构和油冷却方式下，换流变压器中可能存在较多的油流带电问题。通过分析油流带电的产生机理、影响因素、抑制措施和换流变压器的结构特点，研究了换流变压器的油流带电问题。研究表明，降低油速和改善绝缘(特别是油道)设计是减少油流带电问题的最重要措施。开展全电压空载试验等可检验、监测换流变压器的油流带电问题是否严重，此外，向绝缘油中添加电导率调节剂或电荷抑制剂也可降低油流带电的倾向。     

三峡电站升压变压器的若干问题

三峡电站升压器属于超高压特大型变压器，它的安全可靠性直接影响三峡电站的经济效益。本文根据国内外有关资料，分析了变压器发生内部故障和事故的原因，以及发生各种故障的统计概率。重点阐述了取消无励磁调压开关的必要性和经济性。同时根据三峡电站的特点，对变压器的冷却方式和装设发电机保护开关问题提出了建议。     

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.     

Development and calibration of a network-based streamingelectrification model for core-form transformer structures

Streaming electrification occurs in large power transformers when oil circulated for cooling purposes acts to separate charges from the Debye layer on the cellulose insulation surfaces. This phenomenon is believed to have caused several catastrophic transformer failures and remains to be satisfactorily understood in realistic geometries. A network-based streaming electrification model is presented which utilizes single winding ducts as the basic element to investigate a core-form structure. The network is first analyzed using hydraulic duct parameters to calculate the oil flow distributions within the structure. This data is then provided to the electrification solver which predicts the charge densities at each duct outlet. The charge density results are ultimately used to determine the streaming potentials at each node based on an a suitable matrix of leakage resistances. Development of the network model is presented along with empirically-based calibration data for a realistic section of core-form transformer geometry     

Medium-size distribution transformer diagnostics

An improved method of degradation diagnosis for medium-size distribution transformers is described. The proposed method uses refined criteria of degradation for specific application for 200- to 1000-kVA range transformer diagnostics. The new criteria were established with a 95 percent confidence limit of data after extensive case studies focusing on the relationship between the amounts of CO and CO₂ generated in transformer oil and the length of operating time of the transformer. Another feature of this diagnostic technique is the provision of a capability to estimate the thermal history of the insulation material by examining the amounts of certain trace products of decomposition present in the transformer oil. For this purpose, a thermal history discriminant chart was devised by application of a canonical discriminant analysis method.     

油浸式电力变压器动态热路改进模型

油浸式电力变压器绕组的热点温度是指导变压器负载运行方式和影响变压器绝缘寿命的重要参数,准确计算绕组热点温度具有重要意义。在分析运行变压器散热过程的基础上,考虑油箱外壁与周围环境的热量传递,利用传热学原理和热电类比方法,定义非线性热阻和集总热容,并考虑油粘度随温度的变化,建立电力变压器动态等效热路的改进计算模型。将模型的计算结果与实验室自然油循环自然空气(oilnatural-air natural,ONAN)冷却方式下100 kVA/5 kV油浸式温升试验变压器实测数据和IEEE Std C57.91推荐方法计算值进行对比,比较结果表明:通过改进模型计算的变压器顶层油温和绕组热点温度具有较高的精度。     

大功率变压器冷却器的改造与维护建议

冷却器是电力变压器的重要组件之一,它可对电力变压器运行过程中产生的热量进行散热冷却,保证变压器连续正常运行。为此,结合韶关发电厂10号主变压器某次冲洗冷却器散热面前后变压器油温所发生的明显变化,说明散热面的清洁程度影响变压器冷却器的冷却能力,指出应重视冷却器散热面的清洁维护工作。同时针对目前大功率变压器冷却器结构上存在的问题,提出了改造建议,以实现利用天然雨水进行清洁散热面的目的,并对在运变压器提出定期在线冲洗冷却器散热面的建议和措施。     

Thermal tests of large recirculation cooling installations for nuclear power plants

The article presents the results from thermal tests of some recirculation installations for cooling air in nuclear power plant premises, including the volume under the containment. The cooling effect in such installations is produced by pumping water through their heat-transfer tubes. Air from the cooled room is blown by a fan through a bundle of transversely finned tubes and is removed to the same room after having been cooled. The finning of tubes used in the tested installations was made of Grade 08Kh18N10T and Grade 08Kh18N10 stainless steels or Grade AD1 aluminum. Steel fins were attached to the tube over their entire length by means of high-frequency welding. Aluminum fins were extruded on a lathe from the external tube sheath into which a steel tube had preliminarily been placed. Although the fin extrusion operation was accompanied by pressing the sheath inner part to the steel tube, tight contact between them over the entire surface was not fully achieved. In view of this, the air gap’s thermal resistance coefficient was introduced in calculating the heat transfer between the heat-transferring media. The air gap average thickness was determined from the test results taking into account the gap variation with temperature due to different linear expansion coefficients of steel and aluminum. These tests, which are part of the acceptance tests of the considered installations, were carried out at the NPO TsKTI test facility and were mainly aimed at checking if the obtained thermal characteristics were consistent with the values calculated according to the standard recommendations with introduction, if necessary, of modifications to those recommendations.     

Protection of a Single-Phase Transformer from Interwinding Failure in Windings of Integral Magnetic Transformers

A simple means of protection of a powerful single-phase transformer with integral magnetic transformers has been suggested. The protection has a high sensitivity to the interwinding failure and is based on the measurements of unsymmetry of the leakage magnetic fluxes of transformer windings. This magnetic unsymmetry is determined by the difference of electromotive forces of windings of two magnetic transformers placed symmetrically with respect to the symmetry plane of the protected transformer. It has been suggested to produce the magnetic transformers in the form of a single-layer winding with an alternating pitch, which is wound around a textolite round or rectangular body. The length of a magnetic transformer is taken to be equal to the length of a magnetic core, which allows one to provide independence of protection sensitivity on the location of closed turns on the transformer rod. To measure the difference of the emf of magnetic transformers, the circuit of comparison with a responsive element in the form of a TT-40/0.2 or RT1-P/0.15 current relay has been used. Methods to determine a trigger threshold and sensitivity of the protection to interwinding failure as well as to ironwork failure have been suggested.     

Dynamic thermal modeling of distribution transformers

A comprehensive test program was performed on a 2500-kVA oil natural-air natural cooling mode (ONAN) transformer without external cooling. It is shown that the hot-spot to top-oil temperature gradient depends on the transformer construction. The top-oil time constant formula, which has already been defined and validated in the authors' previous work related to transformers with external cooling, is modified in order to take into account the basic design differences. The results are verified by thermocouple measurements and tests at varying loading current. The hot-spot and top-oil temperature responses predicted by the IEEE Loading Guide, Annex G, are also compared to the measured values.     

主变储油柜缺陷导致的油位异常分析及处理

针对一起主变油位异常缺陷,结合实际油位、显示油位及温度-油位曲线,分析了油位异常的可能原因。计算了指针式油位计摆杆长度,对储油柜容积进行了理论计算分析,结果表明储油柜容积至少应为主变本体油量的10%。指出现有主变存在的缺陷和误差,并提出了处理措施和运维检修建议,为主变验收及维护工作提供了一定的参考。     

高压大型电力变压器冷却系统的改造

回顾了变压器冷却系统的发展过程，提出了高压大型电力变压器冷却系统改造的必要性，给出了变压器冷却系统的改造实例。     

基于GA-BPNN的多频超声波变压器油密度检测研究

变压器油是电力变压器中的主要绝缘物质之一,油的密度指标与变压器的安全运行息息相关。文中基于多频超声波、遗传算法-反向传播神经网络(GA-BPNN)的原理,对变压器油密度进行了预测研究。以电网公司110组变压器油为例,其中100组为训练集,10组为预测集。建立了基于BPNN的变压器油密度预测模型,并将242维多频超声数据作为输入,密度作为输出。通过试验法确定了BPNN的隐层神经元个数,由此建立非线性映射关系,并用遗传算法优化BPNN的各层连接权值及阈值。结果表明,与传统的标准BPNN模型相比,GA-BPNN模型的变压器油密度值与实际值拟合度更高,误差更小。研究结果为检测变压器油的其他参数提供了可靠的依据。     

少标签下油浸式变压器双层故障诊断模型

针对油浸式变压器数据样本标记困难，有标签样本数据量较少，传统故障诊断方法精度低的问题，提出了基于GBDT与K means增益聚类的少标签下油浸式变压器双层故障诊断模型。首先，采用SAE对表征变压器状态的高维特征气体进行降维，去除冗余信息，得到包含变压器运行状态的低维特征向量作为后续分类器的输入；其次，构建双层故障诊断模型；针对无标签样本，引入GBDT方法作为所提模型首层，获取无标签样本的伪标签；为进一步提高诊断精度，提出基于无标记样本伪标签的K means聚类增益，作为新的特征向量，输入末层模型K means用以实现二次诊断的目的。实验分析表明，在少标签状态下，所提的方法可有效提升变压器故障诊断精度，相较于传统方法，在诊断精度上至少提升了6%。为少标签下的油浸式变压器故障诊断提供了新的思路。     

110kV及以上变压器事故与缺陷分析

为了做好变压器设备的管理工作,统计、分析2013年度广西电网在运的110kV及以上变压器设备的事故和缺陷情况。统计、分析结果显示,变压器损坏事故的主要原因有短路冲击、产品设计不合理和过电压作用,而变压器的主要缺陷有冷却系统缺陷、硅胶变色、渗漏油和分接开关缺陷等。根据变压器存在的质量和运维问题提出建议,为变压器设备运维工作的开展和预防事故措施的制定提供依据。     

基于有限体积法的分体式冷却变压器热学三维仿真技术

变压器分体式冷却系统与常规冷却方式的散热器安装位置与安装方式均差别较大。由于分体式冷却系统的特殊性,在进行仿真模型研究时参数制定和模型搭建较复杂,目前对其进行热学仿真的研究较少,且仿真准确性难以验证,需要开展更加深入的仿真研究和试验比对工作。对改造的10 k V油浸式变压器进行分体式冷却方式下的模拟试验,基于模拟试验变压器及分体式冷却器的设置建立了变压器分体式冷却系统的三维流-固-热耦合仿真计算模型,采用有限体积法求解出变压器及分体式冷却器的温度场分布,得到分体式冷却器在不同布置方式下的绕组热点温度。将仿真计算结果与试验数据、IEEE导则计算结果进行比对,结果显示,仿真得到的绕组热点温升、顶层油温升的误差比IEEE导则计算结果的误差分别减小了16.6、15.15 K,验证了该仿真模型的准确性和工程实用性。分析显示,试验模型散热器中心高度增加2 m,热点温度降低了7.9 K;散热器与变压器水平距离缩短3.5 m,热点温度上升了4.1 K,从而获得了分体式冷却布置方式对变压器热点温度变化趋势的影响。     

基于光声光谱法的变压器在线监测技术研究

针对现有电力变压器油中的溶解气体浓度低和复杂的外部干扰信号等问题,监测系统在小信号测量和提取方面存在很大的困难。文中基于光声光谱法原理,提出一种对变压器油中气体进行在线监测的技术方案。通过实验,分析和比较了不同电压、不同时间的变压器油中溶解气体数据,确定故障类型。实验结果表明,光声光谱法可以快速检测出变压器油中溶解的故障气体。该研究为我国电力变压器在线监测技术的发展提供参考和借鉴。