基于电压、电流不平衡度差值的干式变压器匝间短路故障识别方法

干式变压器绕组发生轻微匝间短路时,相电压、相电流等电气量变化甚微,不能作为表征匝间短路故障的敏感特征量,导致相应保护措施缺失,运行过程中设备烧毁事故时有发生。通过建立干式变压器“场-路”耦合仿真模型,利用实际试验和工程计算获取的状态参数,验证模型的准确性。通过建立和分析其绕组匝间短路故障数学模型,提取相电压、相电流不平衡度标幺值的差值,作为判断匝间短路故障的特征量。通过仿真分析不同工况下其绕组发生匝间短路故障时不同电气量的变化情况,论证了所提新故障特征量不仅能提前感知绕组匝间短路故障,而且能够克服固有的三相不对称及不平衡运行带来的影响,有效性、灵敏性兼顾,为实时监测干式变压器绕组匝间绝缘状态提供一种新方法。     

The effect of electrode-holding arms on the electrical parameters of the bus-tube section of current lead in an arc steel furnace

The essence of the electromagnetic effect of metalware located near current-carrying elements has been shown. Aftereffects, such as heating of metalware, additional active losses of power supply, perturbation in the magnetic field, and consequent changes in the active resistance and inductive reactance of the equivalent circuit of a furnace have also been considered. The existing technique of taking into account the influence of metalware located near current-carrying elements on the electrical parameters of the current lead of high-power technological equipment has been examined, with its drawbacks being revealed. A method for increasing the accuracy and range of applicability of the technique has been suggested. To do this, a more universal coefficient of neighboring metalware (CNM) has been introduced. The coefficient allows us to take into account the influence of metallic structures on the resistance and magnetic reactance of the furnace circuit. The results of numerical simulations for a bus-tube section of current lead in a 100-t arc steel furnace (ASF) have been presented. The results of simulations were compared with the experimental data obtained by physical modeling of current lead of a 100-t ASF. A numerical model validated by such a way was used to obtain the dependences of active resistance and inductive reactance and CNM on the geometry of the investigated section and the properties of electrode-holding arms. The obtained dependences are the basis for an engineering technique intended to design current leads for an arc steel furnace.     

Distributed‐element modelling for spiral resonators used in wireless power transfer

In this paper, a circuit model for the printed circular spiral resonators based on the piece electrical equivalent circuit is presented. Lumped circuit elements such as inductors, resistors, and mutual inductances are calculated using the conventional formulae for circular loops, whereas the mutual capacitances are calculated by a numerical algorithm. These capacitances are renormalized by scaling factors derived from a simulation‐based library of the self‐resonant frequency of the spiral resonators. It is shown that involving minuscule effects such as mutual capacitances of nonadjacent turns causes a more accurate estimation of the current distribution and high‐frequency characteristics of the resonator. Finally, a closed‐form formula for estimating the capacitor values is extracted by curve fitting leading to a decrease in analysis time. The proposed model predicts the input impedance, quality factor, and current distribution along the resonator in agreement with the results generated by full‐wave simulation and experimental results.     

Derivation of pumpless reactant recirculation system based on analogy between fluid flow and electrical circuit for proton exchange membrane fuel cell

A pumpless reactant recirculation system that offers several major advantages over conventional pump‐ or ejector‐based recirculation systems is derived on the basis of the analogy between fluid flow and an electrical circuit. According to the electricity–fluid analogy, a fuel cell fluid system, including a cell and a reactant recirculation device, can be equivalently described in an electrical circuit model, in which voltage, current, and electrical capacitance correspond to pressure, reactant flow, and fluid volume, respectively, in a fluid flow. In the electrical circuit model, a switched capacitor (SC) circuit, a very popular electrical circuit, is incorporated as the recirculation device. The operation of the electrical circuit model of the recirculation system is mathematically generalized. Based on the analogy, the electrically described recirculation system using the SC is transformed into a fluid circuit, and the pumpless reactant recirculation system in a fluid flow that uses a flow controller and two check valves for reactant recirculation is derived. Experimental and simulation results in the fluid flow and electrical circuit model, respectively, were in good agreement, verifying that the electricity–fluid analogy and the operation of the derived pumpless recirculation system are appropriate. The experimental performance of a single cell in the derived pumpless recirculation system was stable and durable over 10 h, demonstrating that the water byproduct could be removed from the cell in the derived pumpless reactant recirculation system. © 2014 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

低压开关设备和控制设备过电流保护装置（续一）——过电流条件下的选择性

重点论述了低压电器系统的选择性,包括全选择性和局部选择性,对断路器与断路器、断路器与熔断器、剩余电流保护器与电动机起动器等各类电器元件之间配合的选择性作了说明。为进一步提高系统的选择性,介绍了区域选择性联锁的原理与应用。对各种情况均有举例说明,对电器和电路设计均有参考意义。     

模拟低压限流断路器开断特性的数值方法及其应用

本文提出一种用以模拟低压断路器开断特性的数值方法,它把开断过程分为快速机构动作、电弧停滞、电弧运动和熄弧等几个阶段。在机构动作过程中,采用了磁场、瞬态电路和机械运动方程相耦合的求解方法,计算中考虑了触头间的电动斥力和热脱扣器及其它元件的内阻,电弧数值模型基于实验,这些都导致开断过程计算结果和实测结果比较一致。文中还介绍了提出的模拟方法在预测断路器限流特性、选择最佳结构参数及开断波形数值分析方面的应用。     

基于PIC单片机的电动车正负脉冲式快速充电站设计

针对电动车行驶距离短、充电时间长、补充电能慢等特点,采用以PIC16F877A单片机为核心、大电流正负脉冲充电方式,设计了一款专门用于电动车快速充电的智能快速充电站。结合电动车充电的实际要求,给出了快速充电站的整体方案,并就方案中的主电路、控制电路及由PIC单片机控制的正负脉冲充、放电电路进行了具体的研究。试验分析表明,充电站能够实现对电动车蓄电池的无损伤快速充电,可以在短时间内为电动车补充一定量的能量,满足快速充电的要求。     

基于IEC61850的断路器剩余电寿命监测系统设计

基于触头相对电磨损与相对电寿命法研究断路器剩余电寿命监测功能,并依据IEC61850标准构建数学模型。通过实时监测分/合闸电流及次数实现对电磨损量的监测折算,在此基础上构建适应IEC61850要求的电寿命监测分析系统。该系统可实现采样值的数字化传输与逻辑节点的无缝衔接,确保电流采样和分合闸位置监测数据并行传输时的传输实时性与一致性。实例分析表明,该断路器剩余电寿命监测系统稳定可靠,具有工程应用价值。     

Electronic model of a Ferroelectric Field Effect transistor

Abstract

A pair of electronic models has been developed of a Ferroelectric Field Effect transistor. These models can be used in standard electrical circuit simulation programs to simulate the main characteristics of the FFET. The models use the Schmitt trigger circuit as a basis for their design. One model uses bipolar junction transistors and one uses MOSFET's. Each model has the main characteristics of the FFET, which are the current hysterisis with different gate voltages and decay of the drain current when the gate voltage is off. The drain current from each model has similar values to an actual FFET that was measured experimentally. The input and output resistance in the models are also similar to that of the FFET. The models are valid for all frequencies below RF levels. Each model can be used to design circuits using FFET's with standard electrical simulation packages. These circuits can be used in designing non-volatile memory circuits and logic circuits and are compatible with all SPICE based circuit analysis programs. The models consist of only standard electrical components, such as BJT's, MOSFET's, diodes, resistors, and capacitors. Each model is compared to the experimental data measured from an actual FFET.     

GIS中VFT过电压数值分析简化模型的构建方法

为计算GIS隔离开关操作引起的快速瞬变过程 (VFT)的电压波形 ,首先通过分析各个GIS构件的几何形状、尺寸及空间布置情况 ,结合多年来VFT行波的相关研究结果 ,并按照不能明显影响VFT基本波形和过电压幅值的原则 ,简化了影响VFT波形的各个GIS构件的精确模型。其次 ,以一个由母线、隔离开关、接地开关、断路器、电流互感器、电压互感器和套管等组成的典型GIS单元电路为例 ,检验了模型简化方法的有效性 ,简化模型的构建将有助于分析VFT过电压的形成机制 ,以指导GIS的结构设计     

变结构模型短路电流计算方法

提出了一种变结构模型短路电流计算方法。该方法将断路器作为一条阻抗为零的支路来模拟，运用线性网络特性、定理及变结构与变参数的分析方法，将母线上短路时的短路电流等值转移到断路器两侧，导出了相当于在断路器两侧分别发生短路故障时，流过断路器的短路电流的序分量模型和算法。该方法是短路电流计算方法的一个重要补充，使电气设备选择和继电保护整定计算更容易。通过实例验证了该方法的有效性。     

COMPLEX POWER IN CIRCUITS WITH MULTIPLE REACTIVE ELEMENTS

ABSTRACT

This paper provides a detailed discussion of how complex powers combine in circuits with multiple reactive or phase dependent elements. Reactive powers in different circuit elements are additive by simple addition if and only if either the currents or the voltages are in phase or 180° out; this condition is met by multiple elements on a given circuit branch, and by multiple circuit branches between common nodes. The phase condition is not met between individual reactive circuit elements on different circuit branches, therefore reactive power cannot be determined using simple addition; a more complex procedure is necessary. The results are of direct importance for properly determining energy storage between multiple circuit elements within an electrical grid.     

一种短路电流快速识别电路的研究

尽可能缩短短路电流的识别时间不仅对于微机继电保护具有重要的意义,对正在发展中的电器智能化控制也具有极其重要的意义.本文提出采用硬件电路来实现短路电流的识别,通过原理分析,设计了相应的电路.仿真和模拟实验表明,该电路在各种故障状态下均能在5ms内迅速检测出短路信号.它对微机继电保护、电器智能化等具有重要的意义.     

剩余电流动作断路器的选型和安装

剩余电流动作断路器在防止人身触电、电气火灾及电器设备损坏等方面,可以起到很好地保护作用.介绍了其在选型和安装时的注意事项,通过对典型电路的分析,给出了正确的接线图.为查找剩余电流动作断路器脱扣故障原因,提供了查找故障的流程图.     

基于耦合漏感的四绕组变压器暂态模型及短路计算

为确保含四绕组变压器的变电站保护整定可靠性,需研究精细化的四绕组变压器暂态模型及其短路计算等值电路。分析常规变压器等值电路的不足,推导了修正的耦合漏感等值电路,根据三相三柱式四绕组变压器的拓扑结构,运用对偶性原理建立了基于耦合漏感的四绕组变压器电路-磁路暂态模型;利用漏磁路的互阻抗远小于漏阻抗的特点,推导了用于短路计算的四绕组变压器简化等值电路以及零序阻抗。根据某地220 k V变电站实例进行仿真计算,结果表明所提出的四绕组变压器暂态模型及短路计算方法能够更准确地计算含四绕组变压器变电站的短路电流。     

Calculation of a Valve Magnetic System of Maximum Current Release of a Circuit Breaker

Circuit breakers are one of the most widespread electrical devices in control and distribution systems that use electric energy fluxes, providing protection from short circuits and current overloads. First and foremost, circuit breakers should provide a high operation speed at shutdown, which can be achieved with low weight and significant electromagnetic forces. For approximate determination of magnetic system dimensions, network analysis methods are used. In addition, the model of magnetic field structure can be substantially simplified. The conductivity of air gaps between the ferromagnetic elements of a magnetic system can be described by a modified method of probable paths of magnetic flux, and the resistance of ferromagnetic elements (magnetic potential drop) is taken into account by means of a mathematically expressed magnetization curve (for steel of 10895 grade).     

表征开口式电流互感器工作原理的解析模型

传统电流互感器一般采用闭磁路铁心设计,但受铁心材料存在磁饱和的限制,其在一次电流回路发生短路故障时,出现的直流电流分量会严重影响电流互感器的性能,导致其测量电流值的误差可能非常大。开口式电流互感器通过在磁路中引入空气隙,大大增加了磁路阻抗,可有效避免铁心饱和对电流互感器性能的影响。从开口式电流互感器的基本磁路和电路时域方程出发,建立了考虑二次侧负载效应时表征开口式电流互感器工作性能的解析模型。讨论了开口式电流互感器的不同参数对其工作性能的影响。所建立的解析模型,对实现测量用电流互感器与保护用电流互感器的兼容,以及提高用于电能表在线检测的钳形电流互感器测量准确度,均具有理论指导价值。     

旋转型行波超声电机的等效电路模型

在推导旋转型行波超声电机定转子运动拉格朗日方程和压电陶瓷电流方程的基础上,建立了超声电机的等效电路模型。并通过测量单相定子导纳、由摩擦层和转子材料特性参数估算模型中相关元件的值和解析计算电机输出功率及摩擦损耗的方法,对模型进行简化,并获取其中各参数。将电机不同负载转矩及驱动频率的工作条件考虑在内,以电机的等效电路模型作为驱动器的电气负载来设计驱动器参数。给出了理论计算同实测的结果,验证了等效电路模型的正确性和有效性。     

影响电力系统短路计算结果的原因分析

电力系统短路计算是电力部门经常进行的基本计算,其计算结果是设备选择、继电保护定值整定的依据。无论使用调度自动化中的短路计算软件,还是使用继电保护定值整定软件,各种软件或算法的计算结果可能出现差异。产生差异的原因较多,分析表明主要原因有:(1)近似计算中各节点的正序正常电压处理不一致;(2)近似计算中变压器模型的等值阻抗处理方法不同;(3)详细计算中,由于未考虑分接头影响,至使变压器模型选择不当。变压器模型对短路计算的影响很大,建议采用C IM变压器模型,该模型具有原理正确和使用方便的特点。