三相多芯柱电力变压器的谐波模型研究

提出了一种基于铁芯拓扑结构的三相多芯柱电力变压器谐波建模的新方法，将三相变压器用一组电路和磁路方程来描述，选用激磁主磁通和磁动势作为联接电路方程和磁路方程的中间变量。将三相变压器的谐波建模问题归结为三相变压器激磁电流的分析和计算，详细阐述了三相三芯柱变压器和五芯柱变压器激磁电流的计算和分析方法。在该模型中用单值磁化曲线来描述变压器铁芯的饱和效应，而涡流、磁滞和杂散损耗用三个等值电阻来模拟的。作者还讨论了建立相坐标下三相变压器谐波模型的基本方法。     

牵引供电网络谐波分析

介绍了电力系统中典型元件如同步发电机、变压器、输电线等的谐波阻抗模型,并介绍了电力系统分析软件包PCFLO的使用流程。使用软件包PCFLO针对沈阳地铁二号线进行谐波分析,最终给出系统各节点的谐波电压畸变率及各支路的谐波电流含有率,给实际运行提供了一些信息。     

基于ATP的三相变压器励磁涌流仿真研究

利用ATP中电力系统模块建立三相变压器的仿真模型,对励磁涌流进行谐波分析,发现励磁涌流中含有大量的高次谐波和直流分量。对于三相变压器,励磁涌流的波形不仅具有单相变压器励磁涌流波形的所有特征,还受到变压器绕组接法的影响。分析了三相变压器在不同剩磁情况下的电流波形,发现变压器剩磁对励磁涌流的波形有着显著影响,它直接影响着变压器差动保护是否能够正确动作,为抑制不平衡电流提供依据。     

电气铁道三类牵引变压器输入电力系统的不平衡谐波分析

本文通过对电气铁道了Y/Δ-11和V/V牵引变压器三相不对称运行和T接(scott)牵引变压器两相负荷不平衡运行的谐波分析,提出了电气铁道输入电力系统不平衡谐波的序谐波和线谐波电流概念并对上述3种牵引变压器进行了计算。(输入系统的负序(基波)电流用谐波电流统一公式计算)。讨论了各次线谐波和序谐波电流以及负序(基波)电流随供电臂机车电流的变化规律。 文中对上述3种牵引变压器输入系统各次谐波电流的特点和负序(基波)电流的大小作了比较。并将国内外其它几种牵引变压器等效为上述Y/Δ-11或T接牵引变压器,以便利用所述公式计算它们输入电力系统的不平衡谐波。     

特高压交流系统三绕组自耦变压器非线性模型的研究

建立精确的自耦变压器非线性模型是对1000kV交流输电系统谐波特性进行仿真分析的基础。本文基于单相三绕组自耦变压器的电磁关系,充分考虑激磁阻抗的影响,提出了一种适用于谐波分析、易于仿真实现的单相三绕组自耦变压器的非线性模型,然后分别引入ir-u和il-u瞬时特性曲线来求解激磁阻抗,并详细介绍了曲线的数值模拟方法。结合我国晋东南-南阳-荆门1000kV特高压交流试验示范工程中的主变参数在PSCAD/EMTDC中进行了建模和仿真,证明所建立的模型能够比较准确地反映自耦变压器的饱和特性,为搭建完整的1000kV交流输电系统仿真模型和进行其谐波特性分析提供了必要条件。     

一种新型单相并联型有源电力滤波器

提出一种基于谐波磁通补偿原理的单相并联型有源电力滤波器。并联变压器的一次侧绕组与谐波负载相并联,二次侧绕组与逆变器相联,通过对变压器一次侧电压方程分析可知,当采用逆变器在变压器的二次侧注入与一次侧谐波电流呈一定补偿系数的谐波电流时,变压器一次侧对谐波电流呈现近似为零的低阻抗,而对基波电流呈现很大的励磁阻抗,从而输入电力系统中的谐波电流流入变压器支路。通过建立系统的数学模型进行了系统的稳定性分析及稳态误差估算。实验表明,该新型单相并联型有源电力滤波器简单可靠,并取得了较好的滤波效果。     

含单相变压器电路的谐波问题

本文用沃尔特拉级数方法研究了单相变压器非线性激磁特性对电路谐波的作用。分析表明,在一定情况下,可以近似地用叠加原理计算电路的谐波,而且谐波阻抗近似地接近一常复数。论文对单相变压器戴维南等效电路的等效(谐波)阻抗的一种看法,作了评价。     

变压器励磁支路谐波的诺顿等值电路

1.引言在电力系统的稳态分析中,通常不考虑变压器的励磁电流,甚至在谐波的深入研究中所采用的变压器模型也不例外。虽然变压器励磁电流相对较小,但却含有很大的谐波成分。因此,它们在谐波分析中可能是重要的,因规程所允许的每     

单相电力变压器空载电流谐波研究

提出了一种求取单相电力变压器空载电流谐波的计算程序，使用具有数字录波的数据处理功能的计算机自动控制谐波测试装置，对变压器试品进行谐波实测，并对结果与计算进行了对比，阐明了磁滞影响，同时给出了相应的修正。     

电铁牵引变电站接人电力系统谐波和负序分析

通过某电气铁道工程牵引变电站接入电力系统谐波和负序(基波)的计算分析,介绍了电气铁道牵引站产生并注入系统的谐波电流和引起的三相电压不平衡度的计算方法.针对该电气化铁道工程设计中采用三相变压器或单相变压器的不同方案,对电气铁道牵引站产生并注入系统的谐波电流和引起的三相电压不平衡度进行了计算分析.     

Transformer magnetizing current and iron-core losses in harmonicpower flow

The problem of modifying the harmonic power flow analysis to permit the inclusion of nonlinear anisotropic transformers and computation of their iron-core (and copper) losses are discussed. The nonlinear model used for transformers is capable of simulating saturation of iron-cores, anisotropy of laminations, and the iron-core and copper losses associated with anisotropic transformers, but simple enough to be included in the harmonic power flow algorithm without deteriorating its convergence properties. The dependency of iron-core losses on the maximum value of the total (fundamental and harmonic) flux density and the fact that iron-core losses are a function of the waveform of the induced voltage-that is its harmonic phase shifts with respect to the fundamental phase angle-are included. The induced voltage is transformed from frequency domain to time domain: the instantaneous induced voltage and the computed λ-i characteristics are employed to compute the instantaneous magnetizing and core-loss currents. Thereafter a transformation is made from time domain back to frequency domain to compute the fundamental and harmonic components of the above-mentioned currents. Therefore, transformer harmonic couplings are properly modeled and included in the analysis. The modified harmonic load flow formulation is applied to a balanced three-phase feeder consisting of a grounded-wye, grounded-wye nonlinear anisotropic transformer and linear and nonlinear loads     

变压器空载合闸励磁涌流的仿真分析研究

变压器在轻载或者空载的情况下合闸通电的时候,可能变压器的一次侧绕组中流过励磁涌流。励磁涌流出现的原因是在变压器铁芯被拖入饱和区甚至是深度饱和区,励磁涌流对变压器自身和对电网中的电能质量都有不利影响。基于Matlab对单相变压器和三相变压器的合闸涌流进行了仿真研究,同时对变压器空载合闸涌流的特性进行了深入的分析,对变压器差动保护的精确整定,以及对变压器空载合闸励磁涌流的抑制方法提供了突破口。     

变压器空充下的励磁涌流二次谐波特性分析

针对近年来变压器空充试验时,电流的二次谐波含量低于保护整定值导致差动保护误动作的问题,首先利用2条不同斜率的直线对变压器磁化特性曲线进行拟合,推导出不同空充电压下励磁涌流二次谐波含量的表达式,进而基于有限元分析软件搭建并验证了一台14 kVA单相变压器以及一台325 MVA三相变压器的仿真模型,然后对验证过的模型进行了变压器空充仿真。研究表明：在考虑铁芯磁化曲线起始部分存在非线性特征的情况下,空充电压小于临界电压时,励磁涌流中含有少量二次谐波;空充电压等于临界电压时,励磁涌流二次谐波含量达到峰值;随着空充电压等级的提高,励磁涌流二次谐波含量呈现先增后减的趋势。     

Modeling and simulation, and their validation of three-phasetransformers with three legs under DC bias

This paper proposes a new model for three-phase transformers with three legs with and without task under DC bias based on electric and magnetic circuit theory. For the calculation of the nonsinusoidal no-load currents, a combination of time and frequency domains is used. The analysis shows that (1) asymmetric three-phase transformers with three legs generate magnetizing currents with triplen harmonics not being of the zero-sequence type. (2) The wave shapes of the three magnetizing currents of (asymmetric) transformers are dependent on the phase sequence. (3) The magnetic history of transformer magnetization-due to residual magnetization and hysteresis of the tank-cannot be ignored if a DC bias is present and the magnetic influence of the tank is relatively strong, e.g., for oil-cooled transformers. (4) Symmetric three-phase transformers with three legs generate no-load currents without triplen harmonics. (5) The effects of DC bias currents (e.g., reactive power demand, harmonic distortion) can be suppressed employing symmetric three-phase transformers with three legs including tank. Measurements corroborate computational results; thus this nonlinear model is valid and accurate     

Power differential method for discrimination between fault andmagnetizing inrush current in transformers

To avoid the needless trip by magnetizing inrush current, the second harmonic component is commonly used for the blocking differential relay in power transformers. However, the second harmonic component in fault current is increased by the introduction of underground 500 kV lines. This paper describes a new method to discriminate internal fault from inrush current by the sum of active power flowing into transformers from each terminal. The average power is almost zero for energizing, but an internal fault consumes large power. To check the performance of this method, actual inrush current and voltage waveforms of a 500/154 kV transformer are accurately measured by digital equipment. The usefulness is confirmed by applying the method to the measured inrush and simulated fault data     

电力机车在电力系统中形成谐波的潮流计算与分析

电气化铁路的投运使得山西电网谐波问题愈加严重,本文以丰沙大铁路为研究对象,分析了Y/Δ-11牵引变换相接线输入系统的谐波源相位关系,建立了考虑系统电压相位和电压畸变的韶山Ⅰ型电力机车谐波模型,应用电流注入法研究了三相不平衡系统的谐波及负序分布问题,用所编程序计算了山西雁同电网在电力机车不同运行方式下的谐波和负序。     

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.     

变压器励磁涌流负序二次谐波特征及机理

空载合闸产生的励磁涌流是导致变压器差动保护不正确动作的主要因素,同时也会造成电网中谐波、电压暂降等电能质量问题。交直流混联电网中,换流器的谐波耦合特性使得交流电网中的谐波会引起直流保护的误动作,导致直流闭锁,威胁电网安全运行。文中基于变压器铁芯近似磁化特性曲线,推导了励磁涌流及其中二次谐波分量的解析表达式,分析了合闸参数对负序二次谐波分量的影响,指出由于断路器开断引起的三相平衡性剩磁不会造成励磁涌流中二次谐波以负序为主的现象,只有三相非平衡性剩磁才可能引起励磁涌流中的二次谐波呈现明显的负序特征。PSCAD仿真验证了分析及结论的正确性,为解决工程实际问题提供了理论依据。     

A Kalman filter based digital percentage differential and groundfault relay for a 3-phase power transformer

The design and real-time implementation of a Kalman-filter-based digital percentage differential and a ground-fault protection scheme for three-phase power transformers are presented. A set of eleven-state Kalman filters is used to estimate the fundamental and up to fifth harmonic components of the transformer current signals. The protective relay is equipped with an even harmonic restraint during magnetizing inrush conditions and a fifth harmonic restraint during overexcitation conditions. The restraint during external faults is provided by means of a percentage differential characteristic. The relay operates in half a cycle during internal faults. In order to achieve sensitive ground-fault protection, separate primary and secondary ground-fault protection are provided. The relay algorithm is implemented on a single TMS320 digital signal processor and tested in real time using a three-phase laboratory power transformer