关于小电流接地系统中谐振过电压的分析与探讨

在小电流接地系统中出现谐振过电压时,会造成电力设备损坏,对电网安全运行产生不良影响。结合运行中的实例,阐述了谐振过电压的产生原因以及出现基波谐振过电压、高次谐波或分次谐波谐振过电压时的不同特征,提出在电磁式电压互感器的开口三角绕组接入适当阻尼电阻、在母线上加装对地电容、采取临时的倒闸措施、选用励磁特性较好的电压互感器或电容式电压互感器等可行预防措施。     

关于小电流接地系统中谐振过电压的分析与探讨

在小电流接地系统中出现谐振过电压时,会造成电力设备损坏,对电网安全运行产生不良影响.结合运行中的实例,阐述了谐振过电压的产生原因以及出现基波谐振过电压、高次谐波或分次谐波谐振过电压时的不同特征,提出在电磁式电压互感器的开口三角绕组接入适当阻尼电阻、在母线上加装对地电容、采取临时的倒闸措施、选用励磁特性较好的电压互感器或电容式电压互感器等可行预防措施.     

CVT铁磁谐振引起的二次电压升高原因分析及对策

电容式电压互感器由电容元件和非线性电感组成,当有外部扰动时,电容式电压互感器内部有可能产生铁磁谐振．导致二次电压异常升高。在一起电容式电压互感器二次电压异常情况处理过程中,通过二次回路检查、停电试验和解体检查等步骤,分析认为引起电容式电压互感器二次电压异常升高的主要原因是发生铁磁谐振以至烧毁阻尼器．并从理论上对该现象进行了深入分析,最后提出建议以预防类似故障的发生。     

CVT铁磁谐振引起的二次电压升高原因分析及对策

电容式电压互感器由电容元件和非线性电感组成,当有外部扰动时,电容式电压互感器内部有可能产生铁磁谐振,导致二次电压异常升高。在一起电容式电压互感器二次电压异常情况处理过程中,通过二次回路检查、停电试验和解体检查等步骤,分析认为引起电容式电压互感器二次电压异常升高的主要原因是发生铁磁谐振以至烧毁阻尼器,并从理论上对该现象进行了深入分析,最后提出建议以预防类似故障的发生。     

电容式电压互感器谐波模型建立及测试分析

对电容式电压互感器谐波测试精度所受的影响进行研究,考虑杂散电容、耦合电容对电容式电压互感器的影响,建立电容式电压互感器谐波数学模型,分析一次侧和二次侧的函数关系。对110 kV的电容式电压互感器进行现场谐波测量试验,基于实测数据的对比分析,获得了电容式电压互感器幅频特性曲线和相频特性曲线。     

一个监控铁磁谐振的通用子系统

铁磁谐振是电力系统中一种危害比较严重的故障,它主要是由于电压互感器的非线性电感与线路对地电容匹配,构成谐振回路受到某种激发而产生的.理论分析和实践证明,产生谐振的频率是多种的,通常有3次谐波谐振、基波谐振、1/2分频谐振和1/3分频谐振.无论是哪种频率的谐振,都可能使电压互感器产生过电压或过电流,造成电压互感器的绝缘损坏甚至将其烧毁.所以,适时监控电力系统的铁磁谐振更具有实用价值.本文介绍了一个在变电所微机监测系统中监控铁磁谐振的通用子系统,它只从主机取     

对以电磁式电压互感器为谐波源的谐波谐振的分析

对电力系统运行中以电磁式电压互感器为谐波源的谐波谐振的发生原理进行深入分析,通过案例分析论述了电压互感器发生谐振时谐振类型的判断及伏安特性曲线的变化趋势,并对谐振波形运用ATPDraw软件进行了仿真,针对以电磁式电压互感器为谐波源的谐波谐振提出了预防和应对措施,通过减少谐波源、增加回路损耗和采取措施使系统参数处于谐振范围之外来预防和抑制谐波谐振的发生.     

国外期刊(文献)导读

电容式电压互感器(CVT)测量谐波电压研究Harmonic Voltage measurements Using CVTS(IEEE Transactions on power delivery.VOL.20,No.1 January 2005:443-457)作者:F.Ghassemi,P.Gale,T.Cumming,et al.该文介绍了在超高压(EHV)电力系统中直接利用电容式电压互感器(CVT)进行谐波电压测试的方法。目前在超高压电力系统中被广泛使用的电容式电压互感器,原理上是一个调谐在工频(50 Hz)的器件,在谐波频率下具有很大的变比和相位误差,许多国家都明确规定不允许使用CVT进行谐波测试。但与电磁式电压互感器相比,CVT具有体积小、重…     

电力系统局部电路谐波谐振产生原因分析及对策

对在谐波源产生的谐波作用下,电力系统局部电路发生串、并联谐振的原因进行深入分析,论述了电力系统运行中较常见的电磁式电压互感器铁芯饱和引起的谐波谐振的发生原理,针对谐波谐振过电压的危害提出了预防和应对措施,通过减少谐波源,限制注入电网的谐波电流和采取措施使系统参数处于谐振范围之外来预防和抑制谐波谐振的发生。     

电力系统局部电路谐波谐振产生原因分析及对策

对在谐波源产生的谐波作用下,电力系统局部电路发生串、并联谐振的原因进行深入分析,论述了电力系统运行中较常见的电磁式电压互感器铁芯饱和引起的谐波谐振的发生原理,针对谐波谐振过电压的危害提出了预防和应对措施,通过减少谐波源,限制注入电网的谐波电流和采取措施使系统参数处于谐振范围之外来预防和抑制谐波谐振的发生.     

利用适应型励磁控制抑制局部小电力系统低频振荡

以实际小电力系统为研究对象,通过计算机仿真揭示了在局部小电力系统中,由于水电厂调速系统参数设置 不当也会出现低频振荡现象。在仿真分析的基础上,为系统运行提供了合理设置水电厂调速系统参数的方 案;并结合适应型励磁控制进行了抑制低频振荡的仿真运算分析。     

基于类噪声数据的电力系统低频振荡模式辨识方法及应用

低频振荡的监测对于电力系统的安全稳定运行是一个巨大的挑战。提出了基于类噪声数据的低频振荡模式在线辨识方法,该方法将类噪声PMU数据经过预处理后,以ARMA方法计算得到单测点低频振荡模式信息,然后通过聚类方法得到系统振荡模式信息。结合实际发生的一次低频振荡事故,通过比较扰动前和扰动过程中低频振荡模式差异判断振荡类型,并通过势能增量分布法予以验证。     

Dynamics of PFC power converters subject to time‐delayed feedback control

Power factor correction converters are power electronics circuits used as AC‐DC power supplies. These systems are well known to exhibit nonlinear phenomena such as subharmonic oscillations and chaotic regimes. These undesirable behaviors increase the THD and therefore can jeopardize enormously the system performances. In this paper, time delay feedback control is applied to stabilize a two‐stage power factor correction AC‐DC converter when it exhibits these instabilities under traditional controllers. This control technique introduces many advantages to the most and widely used average current mode control through widening the stability domain of the system. By appropriately selecting the time delay feedback gain and the time delay period, the undesirable subharmonic components are eliminated, whereas the desired ones remain unchanged. A harmonic balance approach is used for studying the dynamics of the system under the new control scheme and to obtain the stabilization domain. Copyright © 2010 John Wiley & Sons, Ltd.     

10kV配电网铁磁谐振消谐措施的仿真研究

在中性点不接地配电系统中,由于电磁式电压互感器(PT)励磁电感的非线性特性,在一定条件下容易产生铁磁谐振过电压,严重影响系统的安全运行。文章以嘉兴电力局斜桥变电所10kV配电网为模型,利用EMTP程序对PT高压侧中性点接非线性电阻、串单相PT、经消弧线圈接地、PT开口三角绕组接阻尼电阻或者分频消谐装置等多种消谐措施进行了详细的仿真分析和综合比较,发现中性点串单相PT的方式在消谐能力和全局性方面不如中性点串非线性电阻方式;在非线性电阻消谐方式下,正温度系数(PTC)热敏电阻和三次谐波滤波器可以较好地解决零序电压偏高的问题。此外,文章还定量研究了采用消弧线圈消谐的有效数值范围,分析了分频消谐装置在实际运行中不能很好消谐的原因,并对其他一些消谐方式的有效性进行了探讨。作者的工作可以为电力部门进行铁磁谐振过电压的防治提供较好的参考依据,对提高配电网的供电安全可靠性也有很高的实用价值。     

Subharmonic synchronous mode-locking of a monolithic semiconductorlaser operating at millimeter-wave frequencies

Optical pulse trains at millimeter-wave frequencies are generated by subharmonic synchronous mode-locking of a monolithic distributed Bragg reflector semiconductor laser, by which an initially passively mode-locked semiconductor laser is stabilized by injecting optical pulses at subharmonic frequencies of its resonant frequency. The stabilized pulse trains are characterized in terms of phase noise, timing jitter, locking range and modulation depth under various injection conditions including injected signal power levels, pulsewidths, and subharmonic numbers. It is also shown that subharmonic synchronous mode-locking can provide pulse trains with a very low level of phase noise (⩽-86 dBc/Hz @ 10 kHz offset), reasonably wide locking ranges (4-20 MHz) and low levels of amplitude modulation (96%-99%). Such pulse characteristics are compared with those achieved by the subharmonic hybrid mode-locking scheme, where stabilization is realized by injecting electrical signals at subharmonic frequencies of the laser's resonant frequency. It is shown that subharmonic hybrid mode-locking is only effective at low subharmonic numbers (2-6), while subharmonic synchronous mode-locking can be realized with much larger subharmonic numbers. It is also revealed from the comparison that while subharmonic hybrid mode-locking scheme is simple and cost-effective approach for the generation of high-frequency signals from semiconductor lasers, subharmonic synchronous mode-locking scheme can offer pulse trains using very low-frequency driving electronics with superior performance such as larger locking ranges, and lower levels of phase noise and amplitude modulation     

自适应Hopfield神经网络及其在经济负荷分配中的应用

在传统Hopfield神经网络的基础上,提出了自适应坡度调整法和自适应偏移量调整法的Hopfield神经网络模型(AHNN)。结合传统Hopfeild网络优点,将Sigmoid函数(S型函数)中的恒定参数变为随动,自动调整随动参数运动方向,减小了能量函数的振荡和迭代步数,从而可有效的解决高维、非凸、非线性约束条件的优化问题。将该方法应用于电力系统经济负荷分配(ELD),通过多个算例仿真表明,AHNN有效可行。     

斜桥变电所铁磁谐振过电压的仿真研究

为提高嘉兴电力局配电网面对铁磁谐振过电压的安全性,以斜桥变电所10kV配电网为模型,利用EMTP程序仿真分析了在TV高压侧中性点接非线性电阻、串单相TV(4TV方式)及TV开口三角绕组接阻尼电阻或分频消谐装置等多种消谐措施。结果表明非线性电阻能保持相电压稳定及抑制涌流,正温度系数热敏电阻和3次谐波滤波器可较好解决零序电压的偏高;4TV方式一次侧电流和零序电流过大等问题。还分析了分频消谐装置在实际运行中不能很好消谐的原因。仿真分析结果对提高配电网的供电安全可靠性具有很好的实用价值。     

电容式电压互感器分频铁磁谐振新的分析方法

运用双输入描述函数来确定单个非线性电感电路系统分频铁磁谐振区域和分析系统参数对谐振的影响,提出了电容式电压互感器分频铁磁谐振的分析方法,为改进电容式电压互感器的设计,寻求防范分频谐振措施提供了依据。     

Isolated ferroresonant solutions in transmission lines in the same right-of-way

This paper reports investigations carried out on isolated subharmonic ferroresonant oscillations in a transformer-terminated line due to an energised parallel line on the same right-of-way. The investigation is based on nonlinear dynamics. The motivation for investigating the isolated subharmonics is the reported case of “locking” into a subharmonic ferroresonance solution following a switching operation in the 525 kV system of Bonneville Power Administration (BPA), USA. The initial isolated subharmonic steady states are obtained by a class of temporal methods and it is referred to here as “temporal bifurcation diagram” approach. Starting with initial conditions provided by temporal bifurcation diagram, a continuation procedure predicts multiple subharmonic solutions. Analysis of isolated subharmonic solutions reveals that in general they form a closed loop. Further, odd symmetric subharmonic solutions give rise to supercritical and subcritical pitchfork bifurcations. The paper also reports the sensitivity of isolated subharmonics with respect to the length of de-energised line.     

Chaotic behavior in parametric oscillations

Parametric oscillations which occur in a nonlinear two-phase circuit with nonlinear reactors and capacitors are applied to many kinds of power devices. When the devices are operating under light load, the output voltage of these devices exhibits unstable oscillations, i.e., subharmonic oscillations, quasi-periodic oscillations or chaotic oscillations. This paper analyzes the abnormal oscillations and confirms the validity of the analysis experimentally. In this paper, new circuit equations are presented that can be applied to the analysis of a two-phase nonlinear circuit in which reactor saturation curves are sharp. It is clarified by this analysis that the parametric oscillations of the circuit which contains reactors of moderate saturation characteristics become subharmonic or quasi-periodic with the existence of resistances of the power supply side. Also, when the nonlinearity of the reactors in the circuit is sharp, the parametric oscillations may change into chaotic oscillations in addition to the aforementioned oscillations.