一种直接消除变压器合闸励磁涌流的方法

变压器在轻载或者空载的情况下合闸通电,可能导致一次绕组流过励磁涌流。涌流出现的原因在于变压器铁心因合闸角、剩磁等各种条件的综合作用而进入饱和区甚至是深度饱和区。励磁涌流对变压器自身和电网的电能质量都有不利影响,本文提出了一种基于二阶欠阻尼电路和分压器组成的涌流抑制器,来消除变压器合闸时刻出现的励磁涌流。利用三卷变压器的第三绕组,配以"涌流抑制器"来实现施加在三卷变压器的第三绕组上的电压幅值逐渐爬升,同时保证施加在两个绕组上的电压幅值不同、但相位相同,以起到对励磁涌流的抑制作用。仿真结果证实了该方法的正确性和有效性。     

Magnetizing inrush model of transformers based on structure parameters

This paper proposes a circuit model for the transient period of inrush current in a transformer. The magnetizing inrush model is developed from the structural parameters of the transformer. In the analysis of the magnetization curve, the relationship between the magnetic flux density and magnetic field intensity differs from the ordinary B-H curve; this paper interchanges the B and the H and characterizes the B-H of the magnetic core as a simple tangent function in the H-B planes. Furthermore, the concept of inrush equivalent inductance is also used in the magnetizing inrush model. Using the magnetizing inrush model, an inrush current value can be estimated before the transformer is manufactured. Moreover, in the future, this model can provide the power system with a more thorough transient analysis. During this research, the inrush currents are simulated using the circuit model from ICAP/4. Fourteen actual transformers, each with a different winding structure, are used for demonstration. Experiments and simulations are carried out to examine the proposed method.     

A current-based solution for transformer differential protection.I. Problem statement

This paper analyzes the problem of transformer differential protection. First, the authors review the concept of transformer differential protection. They then analyze magnetizing inrush, overexcitation and current transformer (CT) saturation phenomena as possible causes of relay misoperation. Finally, they summarize the existing methods for discriminating internal faults from inrush and overexcitation conditions     

基于广义瞬时功率的新型变压器保护原理

在差有功法的基础上,提出一种利用广义瞬时功率实现变压器保护的新原理。该原理通过消去变压器回路方程中直接体现主磁通的非线性项,构造了仅含漏电感和绕组电阻的二端网络。根据输入端口的广义瞬时功率直流分量的大小,来区分励磁涌流和内部故障电流。该原理避开了励磁涌流和铁损带来的不利影响,计算量小,易于工程实现。经仿真和动模试验验证,新原理能够快速、可靠的切除变压器内部故障,对空投轻微故障也有足够的灵敏度。     

基于误差估计的变压器励磁涌流识别原理

提出了一种利用波形特征来区分励磁涌流和内部故障新方法。该方法利用励磁涌流为具有间断角的尖项波这一特征，通过比较半个周期时间窗内的实际波形与两个不同频率的参考波型的相似程度来区分励磁涌流和区内故障。动模实验表明：该方法能够快速切除各种情况下的变压器内部故障，保护动作速度达10～13ms。     

A new method to identify inrush current based on error estimation

This paper presents a novel scheme based on error estimation for identification of magnetizing inrush and internal fault conditions in transformers. Because the inrush current is a peaked wave with a dead angle, we can discriminate internal fault current from inrush current by comparing the similarity between the actual wave and two reference waves under two different frequency conditions per half cycle. Experimental results indicate that this technique is effective under different fault conditions, and an operating time of 10-13 ms can be achieved for internal faults in transformers.     

ADAPTIVE DIGITAL DIFFERENTIAL RELAY OF PARABOLIC CHARACTERISTIC FOR TRANSFORMER PROTECTION

ABSTRACT

In the present paper a variable-bias digital differential relay for power transformers protection is proposed. The amount of bias is varied linearly with the value of through current (mean of the currents entering and leaving the transformer). To take care of mismatch between CT ratios on primary and secondary sides of the power transformer, secondary currents of CT are corrected using a precalculated correction factor for the power transformer tap in operation. In the event of an abnormal operation, a fault discriminant based on fundamental, second and fifth harmonic components of differential current is used. It provides discrimination between faults and magnetizing inrush /overexcitation copditions. Trip and indication signals arc issued in the former case, while only an indication is given in the latter case.

The relay scheme is simulated on a personal computer. The advantage of the proposed scheme is its ability to detect even low-level internal faults, which may not be detected by a fixed-bias relay. The relay is restrained from operations on magnetizing inrush and overexcitation. The proposed relay is stable on those heavy through faults on which a fixed-bias relay may operate.     

Application of Park's power components to the differential protection of three-phase transformers

This paper presents a new scheme for power transformers differential protection, in which the concept of the Park's instantaneous differential powers is introduced. The proposed method is able to detect winding insulation failures and to distinguish them from magnetizing inrush current transients. Experimental and simulation results are presented and discussed.     

基于瞬时励磁电感频率特性判别变压器励磁涌流

基于变压器瞬时励磁电感基频分量的有无，提出了判别励磁涌流与内部故障的新方法。涌流时变压器铁心必然经历饱和与非饱和过程，瞬时励磁电感是时变、交替变化的，具有较大的基频分量；内部故障时，变压器铁心工作于线性区，瞬时励磁电感恒为常数，无基频分量。据此，可实现励磁涌流与内部故障的有效判别。但瞬时励磁电感很难精确求取，为方便计算，提出了等效瞬时电感的概念，论证了其基频特性的等效性。动模实验有力地证实了所提方法的可靠性与安全性。     

串接小容量变压器预充磁技术参数设计

串接小容量变压器预充磁涌流抑制技术在船舶电力系统中应用广泛,但缺乏规范化的参数设计方法。推导了串接小容量变压器预充磁技术各次合闸最大励磁涌流峰值解析计算公式。基于此,以预充磁变压器合闸励磁涌流峰值小于系统额定电流,工作变压器合闸励磁涌流峰值小于差动保护启动值为原则确定可选预充磁变压器容量范围;从海洋核动力平台安全性、经济性角度出发规范预充磁电路结构;基于实际建立磁通与预期磁通相位一致原则规范预充磁变压器绕组接线方式;提出相邻周期涌流能量比方法计算变压器建立稳态磁通所需时间,规范预充磁最短合闸时间间隔。MATLAB/Simulink仿真结果表明,在不同合闸角、剩磁情况下,所设计的参数能够保证预充磁合闸过程中变压器差动保护可靠不误动。     

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     

Effects of direct currents in power transformers Part I. A general theoretical approach

The DC component of current circulating in power transformers produces a certain degree of core saturation. The waveshape of the excitation current displays a pulse of high magnitude at each cycle. The width of the pulse depends on the period of the cycle under saturation. This excitation current induces a drop of potential across the primary winding impedance thus reducing the magnetizing voltage and injecting harmonics into the network. Moreover, it is demonstrated that this condition of operation will increase copper and stray losses but will tend to decrease iron losses.In order to study the detrimental effect of direct current, the equivalent circuit of a power transformer has been reviewed to confirm its applicability under partial saturation of the core. For single-phase transformers, the mathematical model developed allows calculation of rms and crest values of magnetizing current, core flux and magnetizing voltage, along with copper and core losses.     

配电网励磁涌流及其概率分布的分析与探讨

为了掌握因配电变压器励磁涌流引起的馈线开关合闸涌流的规律,采用系统抽样法,以某个采样间隔,分别对合闸角和分闸角进行抽样,相互组合构成大量的场景,基于PSCAD/EMTDC对各个场景下流经馈线开关的励磁涌流进行分析,并对结果进行统计综合得出了规律性的结论。研究表明:多台变压器合闸励磁涌流的倍数较单台变压器励磁涌流倍数要小;馈线上励磁涌流的基波分量一般不会超过下游配电变压器额定电流之和的10倍;馈线开关下游配电变压器的容量一定时,其流过的励磁涌流的概率分布规律大致相同而与不同容量变压器之间组合差异关系不大。文中给出了配电变压器总容量3~15 MVA范围的馈线开关合闸涌流的概率分布规律分析结果,可以用于确定瞬时速断保护的电流整定值。     

电力变压器励磁涌流仿真计算的瞬时功率法

本文提出一种基于变压器铁芯材料的基本磁化曲线Ｂ＝ｆ（Ｈ）、变压器铁芯的几何尺寸、空载损耗数值及瞬时功率的概念，对变压器空载合闸时，在各种不同的合闸角及各种不同剩磁的情况下所产生的励磁涌流进行计算的新方法。通过对计算结果的分析，得出励磁涌流的特征，如峰值、波形及间断角的大小同剩磁和合闸角的关系等。本文所提出的方法有助于对电力变压器设计的正确性进行校验及变压器保护的研究。     

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     

特高压变压器的阻抗快速后备保护

研究了由三个单相变压器组成的特高压三相变压器组的后备保护,提出了用阻抗纵联保护作为特高压大容量变压器相间短路的快速后备保护的方案。分析了采用超范围允许式和超范围闭锁式阻抗纵联保护方案的可行性和优越性。说明了阻抗保护受励磁涌流影响小的原理,并用数字仿真证明了此论断的正确性。建立了特高压变压器的仿真模型,仿真结果证明在变压器空投和外部故障切除时产生的励磁涌流不会使阻抗保护误动,而在变压器出口相间短路时能够快速切除故障。采用所提出的保护方案可提高特高压变压器保护的可靠性。     

基于等效瞬时漏电感的变压器保护新原理

在变压器模型回路方程的基础上,应用等效瞬时漏电感,提出了一种新型变压器保护原理。在内部故障的情况下,绕组变形将会导致漏电感参数发生变化;而在正常运行、外部故障和励磁涌流情况下,变压器漏电感等内部结构参数不会发生改变。因此,通过计算等效瞬时漏感参数,可有效地识别变压器的运行状态。2组动模试验分析结果表明,该原理不受励磁涌流的影响,能够迅速、可靠地切除变压器内部故障,对轻微故障也有足够的灵敏度。     

Sympathetic inrush current in a transformer and a method for its identification

This paper studies the sympathetic interaction between transformers. The influencing factors of the sympathetic inrush current, including the system impedance, closing angle and the initial remnant flux of the added transformer, the system voltage, and the neutral grounding mode of the transformers, are analyzed in detail through dynamic simulation. Based on this, a method for identifying the sympathetic inrush current is proposed based on the essential curve feature of the magnetizing currents of the transformers during the sympathetic interaction, taking advantage of the information sharing between substations. The results from dynamic simulation and field‐recorded data show the validity of the proposed method. © 2016 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

基于非饱和区等效瞬时电感的变压器励磁涌流鉴别方法

变压器的等效瞬时电感能够反映其饱和程度的变化,按照差流大小将变压器的运行状态划分为饱和区与非饱和区．分析了变压器经历励磁涌流和短路故障过程中,其等效瞬时电感值在饱和区与非饱和区内的变化范围及特点．根据非饱和区内等效瞬时电感大小区分励磁涌流和短路故障的方法。该方法原理清晰、整定简单、裕度大。试验结果证明,在区内短路故障以及带故障合闸时,该方法能够快速开放差动保护：在励磁涌流时,能够可靠闭锁差动保护,并有良好的抗电流互感器饱和特性．具有工程实际应用价值。