Analyzing the stochastic behavior of ferroresonance initiation regarding initial conditions and system parameters

Power quality and power disturbances are the most important increasing factors throughout electrical networks. Ferroresonance as one of these disturbances can cause quality and security problems. This paper analyzes the stochastic behavior of ferroresonance as a nonlinear resonance phenomenon of the erratic nature and difficult prediction. Furthermore, the impact of different parameters on the initiation of ferroresonance is investigated. It is illustrated that a small change in the initial conditions leads to a large difference in the long-term behavior of the system, and this makes the future of the system unpredictable. Based on the stochastic behavior of ferroresonance some papers took different parameters into account and attempted to identify the basins of attraction for different ferroresonance regions. Here, according to real condition it is illustrated that these basins are highly depending on the initial conditions and there are no transparent boundaries for them. Also, by changing different parameters and initial conditions, the probability degree of ferroresonance initiation is calculated and depicted. Moreover, the impact of source angle on the ferroresonance initiation is investigated.     

电容电压初值对CVT铁磁谐振影响的仿真研究

电容式电压互感器(CVT)的传统等效电路模型中忽略了电容分压器电容电压初值对等效电路模型的影响,然而在CVT暂态时这一因素的影响不能简单地看成是一个误差问题。基于正确的电容分压器的分压比公式,建立了计及电容电压初值的CVT完整的等值电路模型。基于此电路模型,利用Matlab中的电气系统模块库PSB建立了CVT铁磁谐振暂态过程的仿真模型。仿真结果表明,在二次侧短路又消除短路这种铁磁谐振激发方式下,不同的短路时刻和消除短路时刻对CVT的铁磁谐振过程有影响,甚至出现了持续的振荡过程。在二次电压过零短路同时又在其过峰值时消除短路的情况下,电容电压的初值可以抑制铁磁谐振过电压的持续时间,但电容电压的初值较大时,在系统加压瞬间出现的过电压,可能引起二次侧高速继电保护误动作。     

铁磁谐振仿真模型的改进

在中性点绝缘的复杂电网中 ,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 ,利用MATLAB内建的仿真工具实现了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的数字仿真 ,并分析比较了各种不同消谐方法的作用及效果     

铁磁谐振仿真模型的改进

在中性点绝缘的复杂电网中,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,利用MAT-LAB内建的仿真工具实现了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的数字仿真,并分析比较了各种不同消谐方法的作用及效果.     

孤岛模式下的微网多PT铁磁谐振的研究

微网中由于不同的实体独立测量电压,会出现多个PT并联运行的情况。孤岛模式下的微网,失去了主网中性点消弧线圈或小电阻的电压钳位,并联运行的PT更容易发生铁磁谐振。为了提高微网孤岛运行的安全性,深入分析了多PT铁磁谐振的产生机理,同时提出了铁磁谐振的抑制技术。分析表明:通过串一、二次消谐电阻的措施不能可靠消谐,而采用投入一个经消谐电阻接地的中性点的方案具有更好的效果。根据微网的实际运行情况,研究了消谐电阻的选择方法及其控制技术。EMTP/ATP仿真和实际运行验证了所提出方案的有效性。     

Electromagnetic transient study on flexible control processes of ferroresonance

Ferroresonance, which is a common phenomenon in power systems, have threatened the security of power systems for a long time. Although several ferroresonance suppression measures have been applied in power systems, ferroresonance still occurs occasionally. In this study, a flexible control strategy to control different ferroresonant modes is proposed. The behavior of a typical ferroresonant circuit acquired from a ferroresonance testing system to obtain the electromagnetic transient and control details of the control method is also investigated. The key parameters in the control module are determined, including the switching frequency and the coefficients of the proportional–integral (PI) controller. Then, six typical ferroresonant overvoltages are selected as control systems using the proposed method. Given the effect of a damping resistor and fully controllable power electronic switches with a gate signal controlled by a proportional–integral (PI) control system, these six typical ferroresonant overvoltages can all be suppressed in 0.12 s to the non-ferroresonant state after the controller is activated. The electromagnetic transients, including the essential system state quantity transients in the control process, are also investigated. At last, a laboratory prototype is implemented, and the experimental results show that the proposed method is useful for ferroresonant overvoltage control.     

Damping effect of load on the ferroresonance phenomenon in power networks

A generalized approach to the ferroresonance phenomenon, occasionally resulting from power transformers connected to transmission systems, is given. The effect of the transformer load current on the ferroresonance phenomenon at different load power factors is studied. A second-order equation determining the value of the critical load impendance at any load power factor is derived. Also, the effect of the transmission line parameters and the saturation degree of the transformer magnetization characteristic on the value of the critical load current and hence on the ferroresonance phenomenon is shown.     

电压互感器三相励磁特性对铁磁谐振的影响

利用通用的电磁暂态计算程序EMTP,对10kV中性点不接地系统中电磁式电压互感器(PT)饱和引起的铁磁谐振过电压进行了仿真计算。通过三相PT对称和不对称两种情况下的计算,得到互感器三相励磁特性对铁磁谐振的影响。计算表明,系统中三相PT励磁特性不相同非常有利于谐振发生。     

消除中性点接地系统铁磁谐振新方法

由于母线PT励磁特性的非线性，铁磁谐振频率发生在中性点接地变电站的空母线上。本文提出了一种抑制这种现象的方法。在铁磁谐振可能发生之前，同时将数个并联的电阻投入PT二次星形侧；一段时间之后，逐一切除这些电阻，以防再次激发铁磁谐振。电阻值和电阻的个数通过EMTP模拟确定。利用EMTP模拟结果很容易绘制电阻－电压－频度图（R－V－F图），这种图能直观地显示电阻值变化时对谐振抑制效果的影响 。该方法的优点之一是R-V-F科能够很容易地选择消谐电阻；之二是不需要关注谐振的性质，是基波谐振还是分次谐波谐振。基于上述原理，利用PC机、开关卡、可控硅和电阻等，开发了消谐器，并在一110kV变电站成功进行了试验。     

Lightning arrester failure and ferroresonance on a distributionsystem

Since 1987 the Upper Peninsula Power Company (UPPCO) has been experiencing a large number of lightning arrester failures on a portion of their distribution system in southern Marquette County, Michigan, USA. It was in the area of the US Navy's extremely low frequency (ELF) antenna, where the distribution system had been reconfigured so that the transformers were connected line-to-line in order to eliminate interference from the antenna. A study determined that the system was susceptible to ferroresonance during single line faults under lightly loaded conditions and that the overvoltages experienced could be causing the lightning arrester failures. This conclusion was further strengthened by a statistical study which compared the actual number of failures to an expected number of failures, given the systems loading condition and fault rate     

电压互感器铁磁谐振的产生与消除

从本地系统产生谐振的实例出发,分析了电压互感器产生铁磁谐振的机理,包括直接接地系统对地电容引发的铁磁谐振、不接地系统单相接地引起的铁磁谐振和断路器接口并联的电容形成的铁磁谐振.找出了产生谐振的4个方面的具体原因.并从产生谐振的机理出发,全面阐述了消除谐振的8项措施,如在倒母线的操作中增加馈出线路的长度;在电压互感器一次侧中性点接地线上投入电阻;安装零序电压互感器;装设消谐器等.根据谐振的程度大小和出现谐振的具体原因,恰当运用这些措施,就能确保系统的可靠运行.     

铁磁谐振过电压原因分析及预防

对铁磁谐振产生的危害、原因、条件、现象及运行中发生铁磁谐振如何处理进行了阐述：并结合产现场实际发生的一次铁磁谐振现象,分析了具体原因,并制定了切实可行的防范措施。     

General method of finding initial conditions

A general way of finding the initial conditions appearing in systems described by ordinary differential equations is given. The proposed method is based on control theory and graph analysis, and works for both linear and nonlinear systems. It permits an investigation of the initial conditions induced by any one or more of the following: (1) step inputs; (2) impulse inputs; and (3) jumps of system parameters caused by some external effect other than the primary input     

等面积法则在铁磁谐振分析中的应用

电力系统运行经验表明,中性点不接地的电力系统中经常发生铁磁谐振现象,铁磁谐振严重影响系统的安全性、稳定和可靠性.为了有效分析电力系统中时有发生的铁磁谐振现象,将配电网系统经过相模变换将其转化0模网络,建立0模网络的数学模型.引入时变相量的概念,建立系统的时变相量数学模型,分析了系统的三个平衡点.定义了系统的稳定裕度和扰动量的计算公式,创新性地把等面积法则应用到铁磁谐振电路的分析中,并讨论了铁磁谐振的发生与故障时间有密切的关系.把对铁磁谐振的分析由以往的定性分析上升到定量分析,并通过ATP仿真验证了等面积法则在铁磁谐振中的实效性.     

电压互感器三相励磁特性对铁磁谐振的影响

利用通用的电磁暂态计算程序EMTP,对10 kV中性点不接地系统中电磁式电压互感器(PT)饱和引起的铁磁谐振过电压进行了仿真计算.通过三相PT对称和不对称两种情况下的计算,得到互感器三相励磁特性对铁磁谐振的影响.计算表明,系统中三相PT励磁特性不相同非常有利于谐振发生.     

Fast ferroresonance suppression of coupling capacitor voltage transformers

This paper describes a procedure for fast suppression of the phenomenon of ferroresonance in coupling capacitor voltage transformers (CCVT) without major change in the CCVT design. It is shown that it is possible to adjust parameters of the secondary overvoltage protection and the filter circuit so that the ferroresonance can be cleared in a very short time interval. The study cases reported in this paper show that ferroresonance is effectively cleared within two cycles. An implementation of metal oxide varistors (MOV) as part of passive ferroresonance protection is also addressed. The Electromagnetic Transients Program (EMTP) is used for modeling transients and fine-tuning the ferroresonance suppressing circuit. The studies are conducted on the Trench TEHMP161A CCVT.     

HHT在铁磁谐振过电压辨识中应用

铁磁谐振过电压在中性点接地的中高压电网中是常见的故障之一,通常情况下其幅值是正常运行时电压的数倍,为此提出了一种基于希尔伯特一黄变换(HHT)的快速定量辨识铁磁谐振过电压的新方法,运用HHT中的经验模态分解及相关系数法实现主模态分量的有效提取.并对该主模态分量进行Hilbert变换,计算其相对应瞬时幅值、瞬时频率,从而实现对铁磁谐振过电压类型、幅值、诱发时刻的准确定量分析.讨论了HHT在线辨识铁磁谐振过电压的应用,并运用该方法对3种不同类型的铁磁谐振过电压仿真信号及一组实测信号进行了定量分析.研究结果表明该方法能快速有效、准确地定位各种类型铁磁谐振过电压.     

A review of ferroresonance in capacitive voltage transformer

Ferroresonance incidences in electrical power system have been commonly regarded as unexplained phenomenon, which is not critical for utility engineers. As a result, research conducted in this area is limited and the awareness on ferroresonance is relatively low among utility engineers. However, as the electrical system evolves, its complexity increases in line with the increasing risk of ferroresonance. As a result, this paper provides a consolidated review on the research conducted on ferroresonance to highlight its importance. This paper covers the fundamental inductor–capacitor pair for ferroresonance initiation and the modes of ferroresonance, followed by ferroresonance in capacitive voltage transformer (CVT), constituting its impact, initiation, and suppression techniques. The core focus in this paper is ferroresonance in CVT due to switching events, on which the documented literature is very scarce. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Effect of iron core loss nonlinearity on chaotic ferroresonance in power transformers

This paper investigates the effect of iron core loss nonlinearity on the onset of chaotic ferroresonance and duration of transient chaos in a power transformer. The transformer chosen for investigation has a rating of 50 MV A, 635.1 kV, the data for which is given by Dommel et al. (Tutorial Course on Digital Simulation of Transients in Power Systems (Chapter 14), IISc, Bangalore, 1983, pp. 17–38). The magnetisation characteristics of the transformer is modelled by a single-value two-term polynomial. The core loss is modelled by a third order power series in voltage. With nonlinearities in core loss included, three effects are clear: (i) onset of chaos at larger values of open phase voltage, (ii) shorter duration of transient chaos, and (iii) less susceptibility to ‘ jump ’ phenomena.     

小波-PSO在电力系统铁磁谐振研究中的应用

随着电力系统的发展和非线性元件在电力系统中的广泛应用,铁磁谐振给电网和用电设备造成危害问题变得较为突出.由于铁磁谐振检测,既需要检测突变点,又需要进行分频,但是进行小波变换时选择合适的小波基比较困难.将利用小波变换检测铁磁谐振波形的奇异点,从而判断谐振的发生时刻;然后利用粒子群优化算法(PSO)求解非线性铁磁谐振电路方...