互感器励磁特性线性度对铁磁谐振的影响分析

中性点不接地系统中铁磁谐振频繁发生,对电力系统造成了较大损失。实测了三个电压互感器的励磁特性,通过仿真计算,分析了励磁特性对电压互感器发生铁磁谐振的影响情况。在此基础上,对电力不接地系统中应用电磁式电压互感器提出了意见与建议。     

电网黑启动过程中的铁磁谐振分析

在电网的黑启动过程中,可能发生的铁磁谐振线性的本质及相应预防措施,文中分析了母线电容对铁磁谐振的影响,给出了铁磁谐振的本质是电容及电感的充放电过程,及补偿电容对非线性电感的助增作用;给出了在黑启动过程为了避免铁磁谐振的发生,应切除补偿电容器,待黑启动过程完成之后再投入相应的电容器的预防措施。电网最佳黑启动路径的铁磁谐振仿真分析结果验证了该文的上述观点及策略。     

Analysis of Half-Turn Effect in Power Transformers Using Nonlinear-Transient FE Formulation

The half-turn effect is present in transformers if the winding leads are taken out from the different sides of the core. The result is an additional half-turn in one of the core windows in a single-phase transformer, which can create overfluxing of the core leading to excessive losses and temperature rises. This paper presents a methodology to analyze the half-turn effect in power transformers. A nonlinear field-circuit coupled model is used to simulate the half-turn effect; the magnetic field is modeled using the finite-element method. The results show that there is a considerable increase in the flux density values in the core during load loss test, and the increased core losses can be comparable to the values under the rated voltage condition. The results obtained by the proposed methodology are validated with the experimental test results on a single-phase 40-MVA autotransformer. The half-turn effect can be eliminated by taking both the leads from the same side of the core. However, in order to reduce insulation clearances, a few compensating turns are wound on the end limbs to eliminate the half-turn effect. The paper also reports the experimental and the simulation results with the compensating turns. Analysis of the high induced voltages in the unexcited windings of the other phases during the load-loss test on the middle phase of three-phase three-limb transformers is also reported. In the three-phase five-limb transformers, the effects of half-turns in the three phases are almost cancelled under the balanced load conditions; this paper highlights the possibility of the core saturation due to the half-turn effect under appreciable unbalanced load conditions     

中性点接地系统铁磁谐振非线性动力学分析

为了有效地抑制电力系统中铁磁谐振经常发生并严重威胁系统运行安全的复杂现象,应用非线性动力学中相平面、庞加莱截面、Lyapunov指数等方法分析了一典型110kV变电站中由断路器均压电容、系统设备对地电容及电磁式电压互感器铁心电感构成的铁磁谐振电路。通过对不同参数条件下系统中出现的基频谐振、分频谐振及混沌谐振的计算分析,可知应用非线性动力学相关理论及分析方法研究铁磁谐振现象,可确定不同谐振类型及其谐振区域。该法也将为深入理解系统铁磁谐振物理机理,有效防治铁磁谐振提供理论依据。     

35kV系统铁磁谐振事故分析

对一起35kV系统电磁式电压互感器铁芯饱和引起铁磁谐振过电压,造成互感器爆炸、高压熔断器烧毁事故的原因进行分析,提出了防范措施。     

Multi-resolution Wavelet Analysis for Ferroresonance Phenomena in Power Systems

Power systems struggle from many effects, causing over-voltages and over-currents. One of these effects is ferroresonance, which is a non-linear phenomenon that occurs when the system is unbalanced. This article focuses on a 380-kV transmission line from Turkey's electrical power network where ferroresonance occurs during a switching operation. The system is first simulated on MATLAB (The MathWorks, Natick, Massachusetts, USA) model, and voltage variations are obtained. Spectral analysis methods are applied to the signal, and the frequency components of the system are examined for ferroresonant conditions. According to the obtained frequency components, the steady-state behavior of the system is explained.     

Estimation of Magnetizing Characteristics of Pole Transformers in Islanding Area

For the detection of islanding, it is very important to choose the threshold value for the change in the harmonic voltage. In this paper, we propose an analytical model of a pole transformer using a Fourier series and clarify the nonlinear magnetizing characteristics of the pole transformer in an islanding area. After determining the proposed model coefficients from the tests of the pole transformer excited by a sinusoidal voltage, distorted wave voltage tests were performed under conditions in which the third harmonic voltage or the fifth harmonic voltage was superimposed. The results of the testing showed that the magnetic properties vary greatly upon increasing the harmonic component of the voltage. The analytical and measurement results were in good agreement. By using the proposed method, the distributed generators (DGs) can estimate the magnetizing characteristics of the pole transformer by monitoring the connected terminal voltage. Thus, as an active signal for islanding detection, DGs can inject a harmonic current synchronized to the excitation current harmonics of the pole transformer into the distribution network. In the case of DGs equipped with the above functions, there is no need to change the settings of the islanding detection threshold for changes in the harmonic voltage even when there is a change in the excitation voltage or an increase in the number of DGs.     

小波分析在电力系统铁磁谐振研究中的应用

在中性点不直接接地的复杂电网中,因系统突发单相接地故障而激发的铁磁谐振现象经常出现,文章利用MATLAB内建的仿真工具箱对由于电压互感器非线性励磁电感和系统对地电容匹配而引起的铁磁谐振暂态过程进行了数值仿真,利用小波分析对铁磁谐振进行了研究,仿真结果表明,小波分析对铁磁谐振频率的检测是有效的。     

An Auto-correlation Function Based Technique for Discrimination of Internal Fault and Magnetizing Inrush Current in Power Transformers

Abstract—This article presents an efficient method for discriminating magnetizing inrush and internal fault currents in three-phase transformers based on the auto-correlation function. For each phase, the auto-correlation function of the differential current is calculated for a specified range of lags. Their standard deviation is determined in the next step. Criterion function is simply defined as the difference between the maximum and minimum of the auto-correlation function lags standard deviations for the three phases. Performance of the proposed method is evaluated and compared with eight well-known methods by a large number of simulation and experimental data, covering different cases. The results confirm that the proposed technique is more efficient than the other methods from speed response, reliability, and accuracy points of view. To eliminate the current transformer saturation impact on the performance of the method, the currents are compensated by a current transformer saturation correction algorithm. Also, the proposed algorithm is evaluated in the case of a transformer that is fed through a feeder with series capacitors.     

变压器激磁电感对双正激变换器正常工作的影响

分析了双正激DC／DC变换电路中的高频变压器的激磁电感对电路正常运行的影响,导出了高频变压器正常复位时其激磁电感、电路工作占空比、开关频率和开关寄生电容之间的关系,并在3．5kW双正激变换器中得到验证。     

变压器局部放电超宽带射频定位技术的试验分析

超宽带射频定位技术结合局部放电射频信号超宽带检测与天线阵列技术并以最短光程原理为基础,是变压器局部放电定位的新方法。为探索该技术在实际中的应用,研制了频带2～8GHz的新型平面等角螺旋天线作为定位传感器,其放电射频信号的耦合输出波形平均上升时间约150ps,单个脉冲振荡时间约200ps,从而限定时延测量误差200ps;提出了空间网格搜索定位算法,避免传统的解析算法容易由于时延测量值及波速参量的微小误差而导致定位结果发散或误差偏大的缺点。利用新型定位传感器及空间网格搜索定位算法在220kV真实变压器上开展局部放电超宽带射频定位研究并建立了一套能够有效应用的定位系统,对设定故障源的检测灵敏度≥100pC,波速约19.8cm/ns时定位精度最高,平均定位误差约30cm。     

大型变压器的可靠性分析

大型变压器的失效应分成两类加以研究。第一类失效对应于变压器较严重的事故,研究这类失效应把变压器看成是不可修复的系统,其最主要的指标为失效率。本文提出了可靠性数据处理和失效率’计的方法。通过对变压器第一类失效的特点和主要原因进行深入分析,得到了110kv及以上变压器可靠性的控制指标。第二类失率对应于变压器故轻的故障,研究这类失效应把变压     

用UHF法检测电力变压器局部放电的研究

基于 UHF的电力变压器局部放电检测法 ,在实验完成了 5种模型局部放电试验研究后 ,设计并投运了一套适用于现场的 UHF局部放电在线检测系统。试验表明 ,由于油箱外壳的屏蔽作用 ,箱内安装的 UHF传感器检测局放灵敏度较高     

变压器的经济运行方式

分析了电力变压器负荷与损耗的关系 ,通过计算 ,寻求变压器运行中降低变压器的有功功率损耗和提高其运行效率以及提高变压器电源侧功率因数的方法。通过对负荷电流与临界负荷电流进行比较 ,合理选择 35kV终端站和 10kV配电变压器的运行方式 ,达到减少变压器损耗的目的。     

铁磁谐振过电压混沌振荡的理论研究

在中性点直接接地电力系统中,建立铁磁谐振过电压的数学模型,对该模型的异宿轨道进行计算,在此基础上运用Melnikov方法计算该系统的混沌阈值,即铁磁谐振过电压振荡发生的参数区域及混沌产生的条件,并深入探讨其周期解的存在性,为有效控制和消除过电压,抑制过电压中的混沌现象提供理论依据.     

基于磁链分区的大功率中频变压器漏感参数计算方法

基于中频变压器磁场一维等效模型,根据其分布特征,利用磁链分区思想,进行了中频变压器漏感参数解析计算公式推导。在此基础上,假设磁通与其所在区域的绕组不交链或全交链。通过取这两种假设条件下的平均值来简化漏感参数计算过程与解析表达式。通过比较计算与实测结果,证实了这种计算方法的正确性与有效性。     

山东电网变压器类设备统计分析

对截至2007年11月底的变压器、电压互感器、电流互感器等山东电网变压器类设备的台帐统计数据进行了汇总分析。     

电力变压器的故障分析与诊断

介绍了电力变压器运行中几种常见故障的类型及诊断方法。     

直流偏磁条件下电力变压器铁心B-H曲线及非对称励磁电流

基于变压器铁心的直流偏磁特性提出了一种有效获取大型电力变压器直流偏磁条件下绕组励磁电流的方法.首先在按与实际产品1/50比例制作的产品级模型上通过试验研究建立了处于不同直流偏磁水平铁心的磁通一激励电流(φ-I)曲线族,(B-H日)曲线族;其次通过仿真计算考虑了偏置磁通对这些曲线的影响;最后提出了适合变压器工程应用的直流偏磁条件下非对称励磁电流的计算方法.实际测量数据与仿真计算结果的比较表明文中提出的方法是正确的.     

大型电力变压器油纸绝缘含水量的介质响应诊断技术

介质响应技术是检测油纸绝缘含水量的一种无损诊断技术,该技术通过油纸绝缘的介质响应曲线判断其含水量。为推动该技术的发展和实际应用,以电介质理论为基础,对大型油纸绝缘电力变压器的介质响应特性开展了大量研究。结果表明,大型电力变压器介质响应曲线受频率、温度、含水量的影响具有较强的规律。提出了大型电力变压器油纸绝缘含水量的定性分析方法,并通过建立不同含水量、不同温度油浸纸板的复介电常数数据库及设备的X-Y模型,实现了大型电力变压器油纸绝缘含水量的定量计算,计算结果与实际基本相符。