Transformer design and application considerations for nonsinusoidalload currents

The use of adjustable-speed drives requires transformers capable of withstanding high levels of harmonic currents under normal operating conditions. Experience has been that overheating problems are much more common with dry-type transformers than with liquid-filled transformers. Transformer insulation life is determined by the hot spot temperature but confirmation of hot spot temperature rise is one performance characteristic which is ignored in industry standards. This is especially important for transformers rated for nonsinusoidal load currents. The design of transformers for nonsinusoidal load currents should include an analysis of the eddy loss distribution in the windings and calculation of the hot spot temperature rise. Calculations and thermal tests giving only average winding temperature rises are not sufficient. Thermal tests with nonsinusoidal currents and measurements of hot spot temperature rises are extremely difficult on large transformers. The combination of testing and analysis may be the only economically practical approach. Analysis indicates that the dry type transformer hot spot temperature is very sensitive to the eddy loss magnitude and distribution. The Underwriters Laboratories Inc. (UL) K-factor rated dry type transformer and the recommended practices given in ANSI/IEEE C57.110 are reviewed. When purchasing transformers subject to nonsinusoidal load currents, considerations should be given to the manufacturer's development program and capability to calculate the eddy loss distribution and hot spot temperatures     

基于谐波损耗的干式变压器降容研究

IEEE Std C57.110中给出了计算电流畸变情况下变压器损耗的计算方法,其利用绕组涡流谐波损耗因子和杂散谐波损耗因子计算变压器的涡流损耗和杂散损耗,但忽略了绕组高频交流情况下集肤效应和邻近效应引起的附加损耗,计算精度受到一定影响。为了精确计算变压器谐波情况下的损耗,引入了绕组电阻谐波损耗因子,考虑了谐波情况下绕组集肤效应引起的损耗,并据此计算变压器最大负荷电流。在此基础上,研究了电流畸变率对干式变压器降容率的影响,计算结果表明谐波对干式变压器最大负荷电流及带负载能力有较大影响,当谐波畸变率达到60%时,变压器带负荷能力减小一半。     

谐波电流扰动下配电变压器损耗计算与绝缘寿命损失评估

针对谐波电流引起配电变压器损耗增加、热老化加速、绝缘寿命下降的问题,提出了一种计算谐波电流扰动下变压器空载损耗的方法。通过对Yyn0和Dyn11联结的配电变压器在谐波电流扰动下的杂散损耗分析,改进了基于谐波损耗因子的变压器负载损耗计算方法,修正了热点温度计算模型。以98℃为变压器热点温度基准值,利用6℃准则修正了IEEE C57.91中的绝缘纸相对老化因子计算方法。计算及试验结果表明:变压器损耗随谐波电流畸变率增大有较大增加,造成变压器绝缘系统寿命损失,缩短变压器运行寿命。     

谐波对油浸式变压器顶层油温和绕组热点温度影响的研究

研究了谐波对油浸式变压器顶层油温和绕组热点温度的影响。     

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。     

基于谐波电阻的变压器箔式绕组温升在线修正

绕组热点温度是配电变压器在线监测的重要指标,而现有的绕组温升在线计算方法未考虑箔式绕组结构产生的影响。通过配电变压器不同谐波下等效电阻比值对箔式绕组结构进行辨识,然后对比线绕式和箔式两种绕组结构发热差异,对一种通过绕组电阻变化计算绕组温升的算法进行了在线修正。该方法提供了一种通过谐波电阻比值预测箔式绕组热点温度的新思路。     

计算Scott牵引变压器内部温升的热路模型法

牵引变压器的绝缘寿命很大程度上取决于绕组热点温度,研究其内部温升具有重要意义。为此,针对Scott牵引变压器特殊的绕组连接、铁心结构和电气特性,利用热传输原理分析了其内部热量的产生和传输过程;参考电路原理建立了Scott牵引变压器内部热路模型;参照基尔霍夫定理推导了温升的计算式,从而建立了Scott牵引变压器的热路温升计算模型和简化的热路温升计算模型;采用两种热路温升计算模型和IEC温升计算法仿真了同一负荷下的Scott牵引变压器,仿真结果说明了模型的有效性。     

电磁热耦合模型在通风干式变压器中的运用

建立了通风干式变压器绕组温度场的二维电磁热耦合数学模型,并由此计算出变压器箔式绕组因非均匀涡流产生的温度分布,仿真结果与实验数据表明:基于二维电磁热耦合数学计算模型的分析方法是正确、合理、可靠的,为研究干式变压器的温度特性提供了方便。     

油浸式电力变压器饼式绕组温升的影响因素分析

对油浸式电力变压器饼式绕组的油流流速及温度分布特征进行了研究,同时分析了水平油道宽度等参数对油道油流流速及绕组温升的影响。以1台容量为321.1 MV·A的油浸式换流变压器网侧绕组结构为原型,建立了绕组温升的物理计算模型。结合变压器设计原理设置不同的油道参数,计算了绕组油道油流流速以及温度的分布情况,分析了入口油流速度、水平油道宽度、饼式绕组分区数量以及导线匝间绝缘厚度等参数对油道油流流速及绕组温升的影响。结果表明:饼式绕组热点位置位于最后一个分区中心线饼附近;不同的入口油流流速、水平油道宽度及饼式绕组分区数将影响水平油道中的油流速度分布,进一步影响绕组的温度分布及热点温升;导线匝间绝缘厚度对油流速度分布没有影响,但对绕组的温升有一定的影响。     

ITER PPEN项目变压器绕组热点温升分析和研究

利用安德森计算方法对PPEN主变压器绕组热点温升进行了分析和研究,分析了影响变压器顶层油温升和铜油温差关键参数。通过变压器绕组温度场仿真软件验证了该方法的可行性和合理性。     

以箱壁温度为判据的油浸式变压器绕组热点温度计算模型及试验分析

电力变压器的热点温度是影响其绝缘寿命非常重要的因素,准确估计电力变压器热点温度,有助于提高电力变压器的经济与安全运行水平。为此,提出了一种估计变压器绕组热点温度的改进方法。该方法依据变压器热路模型,采用变压器油箱壁温度来估计绕组热点温度。为了验证该方法的准确性,在实验室的试验变压器上进行了负载试验,得到不同负载下的变压...     

光纤传感器在预装式变电站绕组热点温度监测中的应用

针对目前预装式变电站变压器室内部绕组热点温度在线监测困难的问题,提出了一种光纤传感应用方案,通过在变压器内布置光纤温度传感器,可以对变压器的热点温度进行监测,同时结合变压器负载情况对变压器的寿命损失进行评估。额定负载和过负载试验数据表明,该光纤在线监测系统能够准确、及时捕捉到变压器的热点温度,并给出过负载工况下的合理建议。     

改进的油浸式电力变压器绕组热点温度计算和在线监测及运行分析

针对变压器绕组热点温度的计算模型,采用变步长的Runge-Kutta方法对计算模型求解,实时计算变压器的顶层油温和绕组最热点温度。建立针对变压器的实时在线监测系统,实现变压器运行情况的监测分析,采用先进的计算方法对变压器热点温度计算模型求解,提高计算精度;并对变压器短期过负载能力进行科学合理预测。     

油浸式变压器绕组涡流损耗及温升分布研究

利用有限元方法,分析变压器绕组涡流损耗的分布,并基于变压器发热与冷却理论,确定变压器绕组温升分布工程计算方法。通过产品算例的热点温升测量与计算结果比较,检验计算方法的合理性,为油浸式变压器绕组温升分布的合理计算和预防局部过热问题,提供了简单有效的分析方法。     

油浸式电力变压器绕组温度场的二维仿真分析

介绍了用于计算油浸式电力变压器绕组温升的FLUENT模型,对其模拟方案进行了分析,并对油浸式电力变压器绕组的温度场分布及热点温度进行了研究.     

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.     

Air temperature effect on thermal models for ventilated dry-type transformers

The temperature of the air surrounding the windings of ventilated dry-type transformers is an important factor in the cooling of the windings since they are cooled only by the air. In particular, inner windings are sensitive to the air temperature in vertical cooling ducts. This study presents air temperature effect on the temperatures in foil-type inner winding for the dry-type transformers. A transformer rated at 2000 kVA was selected for the research and temperature distribution was calculated under constant and varying air temperatures inside vertical ducts at three different loads. The 2-D transient heat diffusion equation was solved using the finite element method by coupling it with the vector potential equation due to non-uniformly generated heat caused by eddy currents in the foil winding. The calculated temperatures at constant and varying air temperatures are presented together with experimental values. The numerical and experimental results of this study showed that the air temperature affects the accuracy of temperatures in foil-type inner winding greatly.     

Distribution Transformer Winding Losses Due to Nonsinusoidal Currents

Increased transformer winding losses are an important consideration in determining the overall impact of harmonic currents in a power system. Frequently, losses due to harmonic currents are assumed to vary with the square of frequency. The purpose of this paper is to compare winding loss calculations from a finite element method with measured losses in single phase distribution transformers and to test the principle of superposition of harmonic losses due to nonsinusoidal currents. The results confirm both the finite element method and the principle of superposition. Furthermore, it is shown that, due primarily to inaccuracy in measuring 60 Hz eddy current losses, application of the commonly accepted frequency squared rule can yield overly pessimistic loss predictions for typical power system harmonic frequencies.     

影响配电变压器负载损耗测量精度的研究

负载损耗是配电变压器重要的特征参数之一.本文对影响配电变压器负载损耗测量精确度的因素进行研究,分析了直流电阻、绕组温度、测量仪器损耗和短接配件对变压器负载损耗检测的影响.研究结果表明提高变压器负载损耗测量精度的关键因素有:进行负载试验时,应根据变压器连接组别,正确测量负载损耗计算所需的直流电阻;确保负载试验中配电变压器...     

大型变压器绕组温升计算的修正

提出了大型电力变压器绕组温升计算中横向涡流损耗系数的修正方法.