Analysis of internal winding short circuit faults in power transformers using transient finite element method coupling with external circuit equations

Interturn short circuit faults are the leading cause of power transformer failures. If not quickly detected, these faults usually develop into more serious faults, which would result in irreversible damage to the transformer, unexpected outages, and consequential costs. The aim of this research is to obtain a better understanding of the physical behavior of the power transformers in the presence of interturn faults as well as to discover the best indicators for detection of interturn short circuit faults. To this end, a time stepping finite element model of power transformer has been developed to analyze the transient behavior of a real power transformer when the transformer is working under winding short circuit fault conditions. The transient model, coupled with external circuit equations, allows us to simulate the dynamic behavior of the transformer with the real power supply and external loads connections. The FEM computations show the ability of the electromagnetic flux inside the transformer, transformer terminal currents, and circulating current in the shorted turns as useful monitoring parameters for transformer fault detection. Copyright © 2013 John Wiley & Sons, Ltd.     

基于电子式互感器的变压器励磁涌流识别方法

随着电子式互感器研究的日趋成熟及智能变电站的快速推进,智能变电站已广泛采用电子式互感器获取电流及电压信号。传统的变压器保护采用励磁涌流中的二次谐波含量区分励磁涌流和故障电流,从而对差动保护进行闭锁。但在空投或故障切除后恢复供电时,变压器内部发生轻微匝间故障,受非故障相励磁涌流的影响,差动保护可能延迟动作甚至拒动。针对上述原理的缺陷,提出了二次谐波“或”闭锁原理加故障开放的励磁涌流识别方法。试验结果表明,改进方案能明显提高变压器内部故障时差动保护的动作速度。     

New algorithms for power transformer inter-turn fault protection

In the paper new algorithms for detection of internal inter-turn faults in power transformers are described. Such faults are extremely difficult to detect since they induce negligible increase of the currents at the transformer terminals, although the currents flowing at the fault place are very high and dangerous for the transformer to be protected. The algorithms developed are based on the differential equation of the equivalent circuit of the transformer. In one version additional information from a CT installed inside of the triangle of delta side windings is used, which brings very promising results. Theoretical investigations are supported and illustrated with simulation studies performed both with MATLAB and EMTP-ATP programs.     

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。     

一种基于功率损耗突变的变压器匝间保护

在分析了现有的变压器保护的基础上,建立了变压器的电磁暂态模型,对匝间短路故障的暂态过程进行了仿真.针对差动保护在反映匝间故障时灵敏度不足的问题,结合对已有的基于电流电压的变压器保护理论的分析,提出了一种基于损耗功率突变的变压器匝间保护方案.通过实时计算有功损耗与无功损耗之间的比值,故障时该比值将发生较大的突变,从而可测量到轻微匝间故障,可有效的补充差动保护在反映轻微匝间故障的灵敏度不足的缺陷.     

多绕组电力变压器内部短路稳态分析:（一）建模与仿真

电力变压器线圈之间的耦合特性使其内部短路故障的外部特性具有复杂性.为了正确设计和整定变压器内部故障的继电保护方案,必须逐个地针对每种变压器内部短路故障分布情况找到外部故障特征.文中提出了一种分析电力变压器内部短路故障的电路模型和分析方法,并以一台双绕组变压器为例,对线圈内部对地短路、匝间短路、相间短路分别进行了仿真计算,给出了外特性随故障类型和故障位置变化的规律.     

SFZ7-31500/66型变压器缺陷分析及事故防范措施

通过对浦东变2号主变压器烧损后的检测和油、气样色谱分析,确定了变压器故障类型为内部高温放电。该故障变压器经解体检查,发现设计及制造工艺均存在缺陷。鉴于系统内有多台同型号变压器仍在运行,为防止发生类似事故,提出加强变压器绕组变形测试、有针对性调整变压器运行规程等4项事故防范措施。     

变压器轻微匝间故障的保护

首先对一次１１０ｋＶ／１０ｋＶ,３１５００ｋＶ·Ａ变压器的轻微匝间故障进行了分析,继而导出对变压器轻微匝间短路的实用计算方法。最后根据轻微故障的特点提出对变压器比率差动继电器通用特性选择的建议,供同仁参考。     

变压器绕组变形的频率响应分析法综述

目前对绕组频率响应的分析方法主要是基于幅频响应曲线的分析,因此从频段划分、幅频曲线特征的分析及曲线相似指数3方面综述了幅频响应曲线的研究现状,介绍了频率响应分析法的原理,从扫频范围的选择和影响测量的因素2方面讨论了绕组频率响应的测量,认为应建立原始的绕组频率响应数据库,在反映绕组变形程度的曲线相似指数研究方面有待于提出切实有效的量化标准。     

从变压器事故实例看短路试验的必要性

在电力系统中，大型变压器因绕组抗短路强度不足造成绕组失稳损坏事故愈来愈突出。本文通过实例分析了绕组受力情况和损坏原因，指出只有对产品进行短路试验，找出薄弱环节加以改进，才能提高变压器抗短路强度，并提出了抗短路强度的主要措施。     

特高压荆门站串联变压器间单相接地故障分析

对特高压荆门站站用电两级变压器串联的接线方式下发生的小电流接地系统单相接地故障进行分析,指出故障原因是两级变压器之间连接电缆无保护,提出了通过在高压站用变l0kV出线侧加装一个电压互感器的改进措施,以开口三角接线接入变压器后备保护,避免该段电缆无绝缘监测.两级变压器串联接线方式的保护配置,不仅需要将两个变压器看成一个整...     

电力变压器绕组状态实时监测算法

为及时发现电力变压器绕组变形等潜伏性故障,需要实时监测变压器绕组的状态。建立了变压器绕组的数学模型,利用变压器原、次边的电压、电流信号对变压器的短路阻抗进行在线辨识。其方法是:实时采集模型变压器原、次边的电压、电流信号后,针对电压、电流传感器采集信号的特点,应用小波变换除去噪声,再利用基于离散傅里叶变换的高精度相位识别法辨识各正弦量间的相位差,得到各负载情况下变压器绕组等效电路的短路阻抗。利用模型三相变压器搭建的变压器绕组状态监测平台进行实验,结果表明,变压器绕组未发生状态改变时,不同负载情况下短路阻抗的辨识差别不超过0.64%;若变压器绕组发生变形及匝间短路等故障,短路阻抗的变化量达到5.6%以上,证明所提出的监测算法是有效的。     

基于小波包能量熵的变压器振动信号特征研究

利用小波包分解原理将变压器振动信号分解到不同的频段中,然后计算各频段的能量熵值,最后根据该能量熵值来对变压器绕组进行故障诊断。试验结果表明,该方法能够突显变压器绕组的故障特征信息,为变压器绕组的早期故障的诊断奠定了坚实的基础。     

Applying CTs with digital ground relays

Industrial power distribution system substation transformers and generator step-up transformers in power stations often use resistance-grounded wye secondary windings for medium-voltage power distribution. The purpose of this is to limit damage due to ground-fault currents, while providing sufficient fault current for the operation of ground-fault relaying. The relaying used to protect against ground faults in the system may not provide sufficient protection of the transformer winding against internal faults because the backup ground overcurrent relay in the transformer neutral-to-ground connection must be set to coordinate with downstream relays. In order to protect the winding itself, special relays are utilized. Ground differential protection can be provided by digital overcurrent relays in conjunction with auxiliary ratio matching transformers. Ground differential protection can also be provided in multifunction digital relays. Transformer protection relays may include this feature with one of the schemes used with component relays. If a feeder-protection relay is used on the secondary, in some cases, this may have a ground-directional feature that can be utilized for ground-differential protection     

基于漏感变化的变压器式可控高抗匝间保护新原理

鉴于变压器式可控高抗中主电抗器匝间故障率较高,但动作灵敏性偏低的现状,文中在对变压器式可控高抗匝间故障分析的基础上,结合主电抗器的等效总漏感和两侧的漏感值在匝间故障、正常运行及其他运行工况下的不同变化规律,利用比率制动的思想,提出一种新型匝间保护原理.以表征等效总漏感变化的标准差为动作量,以表征两侧漏感变化平稳性的量为...     

The effect of geomagnetically induced currents on the thermal conditions of power transformers

Methods to calculate the thermal processes and temperature of the most heated points of the tank and windings of a power transformer in conditions of flow of geomagnetically induced currents in grounded windings are developed. Dependences of additional loss in the tank and windings are obtained for a TRDN-63000/115/6.3/6.3 power transformer. It is shown that additional losses in power transformer windings are caused by the geomagnetically induced currents and depend on the first and nth harmonic components of magnetizing current, as well as on the load factor of a power transformer. The dependences of excess temperature of the most heated points of windings over ambient temperature on the geomagnetically induced current and load factor are determined. It is found that the excess temperature of the most heated point of winding over ambient temperature is also affected by the total additional loss of active power in the tank caused by the eddy currents at a geomagnetic storm. The acceptable load capacity of power transformers in geomagnetic storms with different intensities is determined in dependence on the ambient temperature. An increase in the load capacity of power transformers above set values in geomagnetic storms can lead to overheating of transformer windings and triggering of transformer gas protection, which will cause an electric power system to malfunction.     

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.     

汽轮发电机转子绕组匝间短路的检测方法

本文介绍了汽轮发电机转子绕组匝间短路检测的各种方法,论述了这些方法用于故障检测的原理和效果,比较了各种方法的优缺点.同时,首次将小波分析方法用于转子绕组匝间短路故障的检测,指出小波分析方法适用于动态非平稳故障信号的特征提取,适合于汽轮发电机转子绕组匝间短路实时的故障检测.     

Electromagnetic force investigation on distribution transformer under unbalanced faults based on time stepping finite element methods

The occurrence of short circuit faults is a major cause behind the windings deformation in the transformers. Mechanical force is proportional to the square of the current. Hence under short circuit condition, it will be very high. These stresses radially or axially affect the transformer windings. Therefore, in the transformer designing, evaluating the effects of short-circuit current and inrush current is very important. In this paper, 2-D and 3-D time stepping finite element methods (TSFEM) that improved in Ansoft-Maxwell, are utilized as Instruments to investigate the leakage flux and electromagnetic forces due to short circuit and inrush current on the windings of 1000 kV A, 10/0.4 kV three-phase, three leg, distribution transformer. Electromagnetic forces in the transformer windings are produced as a result of combination between the current density and the leakage flux density in the winding regions. The study demonstrates that, especially, under single phase-to-ground short circuit fault, leakage flux density on the windings of transformer remarkably increase. The interaction between this high leakage flux with current density, causes the significant increase in the electromagnetic forces in transformer windings.     

基于典型振动规律的干式变压器机械状态诊断

干式变压器在运行中受到电、热、机械等应力的共同作用,可能导致铁心松动和绕组变形等异常故障。振动分析法可以灵敏地反映铁心和绕组的机械状态,适用于干式变压器机械故障的检测。文中构建了干式变压器的有限元模型,仿真探究了干式变压器的振动机理与振动特性,发现干式变压器的绕组振动远小于铁心振动,正常运行状态下振动主要来源于铁心的磁致伸缩效应。文中搭建了干式变压器实验平台,采集并对比分析了正常工况和铁心松动状态下干式变压器表面的振动信号。发现随着铁心逐渐饱和,振动信号不再随电压平方呈线性关系增长,总振动信号峰值增长变快,基频振动信号幅值增长变慢。根据实验得到不同工况下干式变压器的振动信号频谱,发现可将振动信号的基频占比、高低频比作为诊断干式变压器机械状态的特征参量。