A new approach to eliminating of chaotic ferroresonant oscillations in power transformer

Ferroresonance is a complex phenomenon, which can result in thermal and electrical stresses on power system equipments. It can also cause chaotic oscillations in power system. In this paper, a new method is proposed to restrict and damp ferroresonant oscillations, which is based on a new of fault current limiter (FCL). In this method in order to restrict chaotic ferroresonance oscillations, a kind of fault current limiters (FCL) is used which has been used to restrict unwanted high current flow in power system before.To study the ferroresonance nonlinear dynamics, in this paper, the chaos theory is used. By using this theory, the changes in system parameters which can cause chaotic ferroresonant oscillations, can be reviewed and analyzed in details. The behavior of the system during ferroresonance occurrence, with and without using proposed FCL, is discussed in bifurcation and phase plane diagrams. By using these diagrams, the behavioral changes of the system can be easily seen in two cases. The simulation results strongly show the effectiveness of using the proposed FCL for restricting the ferroresonant oscillations.     

Study of the periodic ferroresonance in the electrical power networks by bifurcation diagrams

The principal contribution of this article is to determine the existence zones of the various periodic ferroresonant modes (fundamental, harmonic and subharmonic) intervening in the electrical power network. The bifurcation diagrams are used for this purpose. To be able to plot a bifurcation diagram of a particular solution, it is initially necessary to locate this solution and then to follow it according to a bifurcation parameter. The developed computation code, resulting from the implementation of the Galerkin method jointly with the pseudo-arclength continuation method, has proved to be a powerful and reliable tool to construct these bifurcation diagrams. Indeed, it enables the electrical power network operators to better understand the problems of the phenomenon which had been observed in its network and to foresee new ferroresonance cases.Applied to the single-phase ferroresonant circuits, both series and parallel, we have been able to easily calculate the existence zones of these modes, as well as the stability limits of the system on ranges of broad variation of the parameters.Several results obtained numerically by software MATLAB, as from the real cases, are presented and commented upon.     

Analysis of lightning-caused ferroresonance in Capacitor Voltage Transformer (CVT)

Power networks contain capacitances and inductances that can saturate, presenting opportunities for ferroresonance to occur. Most power equipment is designed through linear theory but ferromagnetic materials are highly non-linear and when they resonate, the non-linearity produces currents and voltages that are larger than usual. Ferroresonance is a complex, non-linear electrical phenomenon. It can cause dielectric and thermal problems through overvoltage, an intrinsic phenomenon present in all networks. A network dynamic response to lightning and switching will be energy storage and release. The transfer of energy will propagate an overvoltage through the network and damage substation equipment when lightning strikes near the substation. Application of conventional mathematics is inappropriate to ferroresonance study in which actual events are simulated. Lightning strikes that occurred near a substation and that led to explosion of CVTs have been reported, so this study investigates the effect of a lightning strike on a tower with a 132 kV Capacitor Voltage Transformer (CVT). Alternative Transient Program (ATP) was used for the simulation which duplicated the lightning-strike effect that causes a CVT to explode.     

高压及超高压故障电流限制技术分析

220kV和500kV高压及超高压故障电流限制技术被认为是保障大电网安全稳定运行、提高供电可靠性和灵活性的有效途径。本文结合国内外高压及超高压领域的几个限流器工程示范项目,对比分析串联电抗限流技术、串联谐振限流技术、分裂电抗开断技术、超导限流技术以及其他混合限流技术的原理、设计和制造关键技术、可靠性和造价,并对各种限流技术的优缺点进行了评述。     

基于MgB2的新型电阻型超导故障限流器的研制和性能分析

超导故障限流器对限制短路电流和短路容量具有重要的研究意义。文中基于MgB2的特性,采用先变形后退火的方法,并利用特制高温玻璃纤维进行绝缘,在退火处理后再通过环氧树脂胶黏剂固化,研制了一台小体积电阻型超导故障限流器样机。同时通过液氦和氦气冷却,对其性能进行测试;通过建立电阻型超导故障限流器的一维热传导模型和电路方程,对其动作特性进行仿真。测试和仿真结果表明该样机限流效果明显,限流百分比可达44%以上,然而限流器的失超长度、超导线材温度和失超电阻随着时间呈非线性变化且限流器的线材并未全部失超。失超恢复时间约为1.5s,可通过交替连接方式满足重合闸需求。最后针对10kV电力系统,提出了MgB2的小体积电阻型超导故障限流器工程设计原理,并分析了其在工程应用中的可行性。     

饱和铁心型超导限流器压敏电阻的实验

压敏电阻可抑制超导限流器断直流时产生的高压,同时加速直流励磁能量的释放以促使限流器交流侧快速退饱和,进入感性限流状态。为验证其保护和能量吸收作用,用NI采集卡、Labview以及其他电流电压传感器和可控的IGBT器件设计和制造了检测控制系统。对不同压敏电压等级的压敏电阻进行断直流的放电实验以验证其抑制电压的保护作用。结果表明:断直流时储存能量的释放是超导限流器产生高压的原因;励磁储能一定且压敏电阻通流量一定的条件下,压敏电压越大断直流产生的电压也越大,同时电流断开时间越小则能量释放时间越小。所得结果为设计更大容量的超导限流器,选择不同压敏电阻的压敏电压和通流量等级提供了实验和计算参考。     

空心超导变压器参数设计对可控阻抗型限流器性能的影响

介绍了可控阻抗型超导限流器的电路结构和工作原理,该限流器由空心超导变压器及PWM变流器组成.故障发生后,通过变流器控制变压器二次侧注入电流的相位和幅值,进而调节限流器的等效阻抗,从而实现抑制短路电流的目的.针对空心超导变压器参数设计对限流器工作性能的影响,以初始补偿电流、不同工作模式下的限流阻抗以及变流器的功率传输为指标,进行了理论研究;以该型限流器在一个三相接地系统的应用为例,利用Matlab建立仿真模型,分析了不同变压器参数下限流器工作性能的差别.仿真结果与理论分析相符,得出如下结论:增大变压器一次侧自感有利于加强限流能力;增加变比会导致初始补偿电流的上升;提高耦合系数有助于降低变流器的无功功率输出.     

不同结构超导故障限流器在电力系统中的应用研究

对不同结构的超导故障限流器(SFCL)在实用化过程中所面临的一些技术关键问题,如动作电流整定、参数选择、失超恢复问题及对继电保护的影响,进行了比较研究。研究表明,高温超导带材制造桥路型SFCL因具有费用低、性能好、可控性强等优点,应成为SFCL工程实践的首选方案。     

桥式超导故障限流器的数字仿真研究

桥式超导故障限流器,它由超导磁体、二极管桥路和直流偏压源组成。超导故障限流器与常规限流电抗器不同之处是:将其接入电网,当电力系统正常运行时,超导体电阻几乎为零,对电力系统运行无影响;当电网发生短路故障时,超导线圈可以无时延地被自动串入线路,从而限制了短路故障电流,使得轻型断路器可以正常动作。通过PSCAD软件对超导故障限流器的运行特性进行仿真分析,证明超导故障限流器在电力系统中应用的意义与前景。     

基于双6RA70的超导限流器励磁电源设计

介绍了饱和铁心型超导限流器的工作原理,分析了励磁过程,为恒压充磁和低压恒流供磁提供了理论依据,提出了直流励磁电源的设计结构,选择6RA70作为电源控制的核心元件,有效地解决了直流电源高压和大电流的控制问题,描述了控制过程中高压充磁和恒流供磁的工作要求和切换方法,通过采用西门子S7-300 PLC组成的Profibus-DP控制系统,实现了数字化网络控制,为限流器的挂网运行提供了参考。     

超导限流器引入配电系统后的短路行为仿真

借助EMTP对10 kV配电系统中引入超导限流器的短路行为进行了仿真。给出了超导限流器的数学模型,着重分析了超导限流器限流电阻和故障检测时间对短路电流峰值、非故障线电压、超导限流器上的电压的影响。仿真结果表明, 增大限流电阻可以显著降低短路电流的峰值,并有利于维持非故障线的电压,但限流器上的电压也会增加。故障检测时间是影响超导限流器性能的关键参数,快速故障检测对提高超导限流器的性能、降低开关开断后的恢复电压非常有利。     

Experimental studies of the improvement of power system stability by superconducting fault current limiters

With increasing demands for electric power, the electric power system is becoming more and more complicated, and the stable, highly reliable delivery of electric power is encountering two major problems, namely, large fault currents and power system instability. In particular, the fault currents occurring in power systems are tending to increase. To solve this problem, superconducting fault current limiters (SCFCLs) have been developed, and it is hoped that they will also solve the problem of power system stability. This paper describes the results of experiments on the improvement of power system stability and the suppression of fault currents with SCFCLs, performed with power transmission simulators. An experiment using an R‐type SCFCL in a power system was performed. An R‐type SCFCL was simulated by using a resistor and an electromagnetic contactor with thyristors. It was found that the inclusion of an SCFCL in the electric power system gives improved suppression of fault currents and improved power system transient stability. © 2000 Scripta Technica, Electr Eng Jpn, 133(4): 41–52, 2000     

超导故障限流器接入电网后单相接地短路距离保护整定的改进措施

当电力系统发生单相接地短路时,超导故障限流器的接入会对其继电保护尤其是距离保护产生很大影响,以电阻型超导故障限流器接入电网为例,首先分析系统发生单相接地短路时限流器的接入对接地距离保护的影响,然后提出一种新的距离保护整定方法,最后采用PSCAD/EMTDC软件搭建模型仿真分析,结果表明在新的整定方式下,测量阻抗误差大大降低,超导故障限流器可以与线路距离保护正确地配合使用。     

超导故障电流限制器的技术参数和要求的讨论

针对应用于电力系统中的各种类型的超导故障电流限制器应具有的 ,特别是有关限流的各种技术参数及要求进行了分析讨论 ,还就超导故障电流限制器参数对电力系统稳定性的影响进行了分析。     

电阻型超导故障电流限制器应用于VSC-HVDC系统的位置优选研究

由于能独立控制有功、无功功率,无换相失败等优点,基于电压源换流器的高压直流输电系统(voltage source converter based high-voltage direct current,VSC-HVDC)系统被认为是未来电网的发展方向。但是,直流故障与交流故障快速有效隔离,成为影响VSC-HVDC系统发展的重要技术难题之一。为了解决VSC-HVDC系统故障隔离问题和限制故障线路过大的短路电流,应用超导故障限流器逐渐被人们重视。提出基于电阻型超导限流器的故障限流方法,并用所设计的两端双极性VSC-HVDC系统,分别在直流线间短路、直流线路接地短路和三相交流短路情况下,比较电阻型超导限流器可行的安装位置并证明所提限流方法的有效性。最后,利用PSCAD/EMTDC仿真提出在VSC-HVDC系统中电阻型超导限流器的最优安装位置。     

适用于两电平电压源型换流器的直流故障清除辅助拓扑

两电平电压源型换流器在35kV及以下电压等级输电场合具有较高的成本效率比,因此被广泛应用于风电并网等低压领域。但是,其不具备直流故障清除能力的特点,给电网设备安全造成了较大的影响。基于以上背景,文中提出了适用于两电平电压源型换流器的直流故障清除辅助拓扑。该辅助拓扑使用超导故障电流限制器,大幅降低了故障电流;基于电流谐振的思路,可实现在电流过零时将故障清除。采用该辅助拓扑的直流故障清除方案,相比于采用交流断路器的方案,具有清除时间短、故障电流小的优点;相比于采用直流断路器的方案,具有电压变化率小、成本低的优点。最后,在PSCAD/EMTDC中验证了所提辅助拓扑的正确性与有效性。     

直流SMC铁心高温超导故障限流器的研究

分析了直流电力系统保护的发展现状,设计了一种铁心型高温超导故障限流器。为了尽量延长限流的时间,限流器的铁心采用软磁复合材料(SMC)。限流器在系统正常工作时对电力系统影响很小,当短路故障发生时,它会很快表现为大阻抗以限制短路电流。基于磁场有限元与电路耦合的计算方法,首先对限流线圈在短路过程中的非线性电感进行精确计算,然后结合计算结果,在电路仿真程序中计算短路电流。通过对比SMC与硅钢铁心材料限流器的限流情况,可以看出SMC铁心限流器对于直流电力系统短路故障的限流效果更好。在短路故障发生后8 ms时,该限流器能将短路电流限制到最大值的12%。     

采用脉宽调制(PWM)控制的新型故障限流器的研究

提出了一种采用脉宽调制原理控制的具有动态串联补偿功能的故障限流器。它主要由以脉宽调制(Pulse Width Modulation,缩写为PWM)原理控制的电感、开关控制的电容器组、限流电感构成。正常时,通过控制投切的电容器组,实现可控串联补偿功能,故障时,通过改变脉冲的占空比可以得到变化的阻抗,达到可控限流目的。用MATLAB进行数字仿真证明了此装置的有效性。     

一种新型故障限流器在电力系统中的应用研究

提出了一种基于集成门极换流晶闸管IGCT和固态电力电子开关的故障限流器,它由电感和IGCT等组成。正常时,串在电路中,基本无能量损耗,故障时控制短路电流大小。通过PSCAD的仿真分析和现场试验,证明了其有良好的限流性能,可以作为电力系统中有效的保护设备。     

SFCL对HVDC系统中换相失败的影响

针对逆变侧换流母线逆变侧发生短路使得交流电压下降和直流电流上升而引起的换相失败问题,分析了换相失败影响因素及桥式超导故障限流器（SFCL）限流原理.在PSCAD/EMPDC仿真环境下,以CIGRE HVDC基准模型为研究对象,将SFCL应用于直流输电系统中,研究SFCL对HVDC系统稳定运行及换相失败的影响.研究表明,SFCL能够限制交流系统的故障电流继而使直流输电系统能快速恢复正常运行状态。