选相抑制交流滤波器合闸涌流及过电压研究

换流站内交流滤波器投入过程会产生较大的涌流及过电压,对其内部元件和母线造成很大的冲击,严重威胁系统安全.文中结合高压断路器在不同开距下的电场分布特性计算出预击穿时间和实际关合时间,运用PSCAD/EMTDC仿真软件建立了直流输电系统模型,仿真分析了计及预击穿特性和机械分散性的选相投切技术对抑制合闸涌流及过电压的有效性,...     

基于高压真空快速断路器的变压器励磁涌流抑制技术研究北大核心CSCD

针对空载变压器在投运过程中产生的励磁涌流问题,文中研究了基于高压真空快速断路器精准动作特性,采用快速选相合闸方式,对110 kV三相变压器合闸过程中励磁涌流进行抑制。在原有主变间隔的SF_(6)断路器和主变中加装本装置,可以不改变原有保护方式和运行模式的条件下,实现涌流的限制。通过对比现场SF6断路器和本装置的实际合闸投运过程中变压器涌流大小,可以发现尽管存在预击穿、剩磁偏差等影响因素,本装置对变压器励磁涌流有较好的抑制效果,具有良好的工程应用价值。     

真空断路器选相合闸空载变压器的试验研究

电力变压器是电网中至关重要的元件,并且是变电站中最昂贵的设备。如果空载时突然把变压器投入电网,由于变压器的非线性,在合闸瞬间会产生很大的励磁涌流,其幅值可达稳态时的几十倍或更高。通常励磁涌流的衰减速度要比短路电流的衰减速度更慢,在上述高幅值的励磁涌流下,很容易引起变压器差动保护装置误动、绕组机械应力增大以及电能质量降低等问题,而真空断路器的选相合闸能很好的解决这个问题。文中在某大功率试验站的6 kV网络试验回路上采用12 kV快速真空开关进行了空载变压器的合闸试验,试验中测量了真空断路器随机合闸、普通选相合闸和检测剩磁选相合闸空载变压器这3种情况下的励磁涌流,测得的涌流大小用于验证选相合闸的效果。试验结果表明与随机合闸相比,选相合闸能够显著减小励磁涌流,检测剩磁选相合闸与普通选相合闸相比更能显著减小励磁涌流,但是即使采用了检测剩磁选相合闸的方法,真空断路器的预击穿特性也对选相合闸效果存在影响。     

基于SF_6断路器动态击穿特性的选相合闸技术

为了进一步降低电容器组及其投切开关的合闸涌流与过电压,介绍了一种改进的SF_6断路器合闸动态击穿特性(预击穿特性)测量方法,并根据合闸动态击穿特性与合闸时间的分布范围,制订了选相合闸策略。研制了1套最高输出电压400 k V的击穿特性测量装置,在1次合-分闸操作中可同时获得断路器在合闸与分闸操作过程中触头间隙的动态击穿特性;对1台126 k V SF_6断路器进行了试验研究,成功获得了该断路器的合闸动态击穿特性;根据该断路器的合闸动态击穿特性与合闸时间的分散性,制定了相应的选相控制策略;理论分析证明考虑断路器特性以后,最大预击穿电压下降了0.015 8~0.336 2(标幺值),合闸时刻的分布范围降低了0.02~0.35 ms;试验结果表明,该控制方案满足设计要求。     

选相投切特高压线路及对其操作冲击绝缘的影响

1000 kV特高压系统的不断发展对输电线路操作过电压允许值提出了更高的要求。如何限制特高压输电线路的操作过电压倍数已成为发展特高压电网所要解决的技术难点。选相投切技术是解决这一难点的重要技术,而相控技术目前发展的瓶颈是对断路器预击穿和机械分散性问题研究的不足。该文结合特高压双断口断路器不同开距下电场强度动态变化过程,计算出合闸预击穿时间,再利用ATP-EMTP软件对1000 kV输电线路进行合理建模以及合闸和重合闸的电磁暂态仿真。仿真结果表明选相投切结合避雷器可有效地抑制操作过电压。操作过电压的降低能够减少线路杆塔空气间隙,进而可以缩减特高压电网投资成本。     

1000 kV变压器励磁涌流及抑制方法仿真研究

采用ATP-EMTP电磁暂态仿真软件,建立了计及铁心饱和与磁滞特性的1 000 kV变压器励磁涌流仿真模型,研究了多种合闸工况下1 000 kV变压器励磁涌流及断路器选相分合闸装置对励磁涌流的抑制效果,结果表明:当考虑断路器动作时间误差时,选相分合闸装置对变压器励磁涌流的抑制效果降低,提出了联合断路器选相分合闸与并联合闸电阻方案,加强励磁涌流抑制效果,保障电力系统安全稳定运行。     

12kV真空断路器投切并联电抗器合闸预击穿过电压的研究

12 kV真空断路器投切并联电抗器时可能会产生合闸预击穿现象,形成危险的过电压。为探明合闸预击穿产生过电压的情况和改进现有合闸仿真模型。笔者在运行电网上对一种型号的12 kV真空断路器合闸并联电抗器进行了一系列的现场试验研究,并对合闸预击穿暂态过程和现象进行了分析。结果显示:该型号真空断路器的合闸预击穿率高达50%,且合闸预击穿相对地过电压均可超过4.0 p.u.。统计得到其合闸操作不同期特性、预击穿暂态过程中断口间介质动态绝缘强度恢复曲线和高频电流熄弧特性,并在ATP-EMTP中搭建真空断路器合闸预击穿MODEL控制模型。考虑电缆三相间的寄生参数,对该型号真空断路器合闸并联电抗器进行三相仿真计算,与试验结果对比分析显示,仿真结果与试验结果基本一致。     

高压SF_6断路器选相合闸技术的应用研究

具备相控功能的高压断路器在国内诸多重点直流工程中得到越来越多的应用。针对某关合交流滤波器场的相控高压断路器在某次合闸操作中未在设定目标相位合闸,导致选相合闸控制偏差较大,造成系统过电压和涌流的事件,结合断路器合闸过程中的预击穿特性,分析选相合闸控制失败的原因,并给出相应的解决办法。     

基于真空断路器预击穿特性的海上风电场集电网合闸暂态过电压仿真研究

海上风电场中压电缆集电系统真空断路器在闭合空载变压器操作中,真空断路器预击穿会在机端变压器的高压侧产生暂态过电压,该过电压与电缆作用产生高频振荡过电压将对变压器绝缘产生损坏。文中研究真空断路器预击穿产生高频暂态过电压的机理,在PSCAD/EMTDC暂态分析软件上搭建真空断路器预击穿现象的自定义模型,并将此模型应用于简化的海上风电场中压电缆集电系统模型,研究合闸初相角、电缆长度和机端变压器位置对暂态过电压的影响。仿真结果表明机端变压器位于机舱且合闸初相角为15°过电压陡度最大,在机端变压器加装扼流线圈和并联小电容的过电压保护装置后,暂态过电压陡度得到了明显的抑制。     

断路器合闸电阻对变压器励磁涌流的影响

为了分析在不同合闸方式下断路器合闸电阻阻值对变压器励磁涌流的影响,使用EMTP软件进行了仿真计算,计算结果表明,断路器合闸电阻对变压器励磁涌流峰值有明显的削弱作用,在确定是否取消断路器合闸电阻时,应考虑到它对励磁涌流的影响。     

DC-DC开关变换器开关工作频率设计

根据DC-DC型开关变换器的工作原理,以Buck型开关变换器为例,讨论了储能电感、滤波电容、输出纹波电压、变换器转换效率与全控型开关器件的工作频率之间的关系,为开关频率的选择提供了理论依据,并进行仿真验证,仿真结果与理论分析一致,表明了参数计算和选择的合理性.分析的方法和结论为其它类型的DC-DC开关变换器的开关管工作频率的分析和设计提供了有效的分析手段和方法,也为实际DC-DC开关变换器的设计和调试提供了新的思路.     

Improved switching mode oscillators employing generalized switching lines

The present work proposes an unusual method for controlling the activation of the switches of switching mode oscillators. The proposed method is in fact a tool for developing switching mode oscillators that are controlled by full variable feedback. The methods developed in the present article rely on characterizing the switching procedure by intentionally moulding the related switching line (the switching line is the line in the state space, where the switches change polarity). The switching line in most of the switching mode oscillators is relatively simple. For example, in many cases the switch changes state in accordance with the output current sign. Hence, the line ‘output current’ is zero, is the switching line in this case. Relatively many advantages are attained by the present moulding of the switching line. For example, oscillators that oscillate even with very low‐quality factor (large load) are obtainable. The proposed method enables a simple way for controlling the output voltage and the frequency of the switching mode oscillator. Furthermore, current limiter property of the oscillator output can be obtained by the method, even in cases where the original oscillator is inherently a voltage source. The output impedance is also made controllable by the method. The successfully improved characteristics are demonstrated by investigating a particular structure, namely, a switching mode series resonant oscillator. Copyright © 2000 John Wiley & Sons, Ltd.     

Photonic switching

Early landmarks in the development of optical communication are briefly reviewed, and the types of device used namely, relational and logic devices, are examined. Three kinds of optical switching networks in which they can be used are described. They are optical space-division switches, optical time-division switches and optical wavelength (frequency)-division switches     

Stabilizing switching

A new idea of using switching to enhance the transient stability of a transmission network is outlined conceptually and illustrated by means of a simple example where the technical implications are given. A realistic system is used to show the benefit of stabilizing switching for a long distance transmission scheme. Depending on the type of fault, where the most severe is the three phase short circuit, an increase of the maximum transmissible power of about 10 percent can be achieved by the switching scheme. The additional benefits of this scheme include reduced fault currents and minimized effects of unsuccessful line reclosure. This scheme also provides a possibility for applying other control devices in stability control, e.g. surge arresters, current limiters and MOS controlled thyristors in the future     

Controlled switching of transformers

A mathematical model is developed to investigate the controlled switching of unloaded transformers. Algorithms of controlled switching that eliminate inrush currents and, vice versa, providing the highest inrush currents for testing, are proposed. The influence of the switch capacity on the character of the recovery voltage is analyzed.     

主变备自投及过载切负荷装置的应用

分析了主变备自投及过载切负荷装置在应用过程中存在的问题,针对该装置的特点,结合实际,提出了相应的解决方案。     

抑制操作过电压的对策

论述从断路器方面考虑的措施及应用上的注意事项。     

Economics of switching fluorescent lamps

Based on side-by-side cost comparison of different switching options, including a combination of parameters based against frequent switching, it is argued that it is economical to turn fluorescent lamps off when they are not needed. Background information to explain the calculation procedures and a sensitivity analysis are included     

Closed-transition switching of essential loads

The design and applications of closed-transition switching to improve performance in transferring all types of essential loads is presented. Application factors are discussed such as load characteristics, the need for periodic testing, anticipation of power failures, desired reliability, and required approvals. Transfer switch design as it applies to both the transfer switch itself and to the associated controls is discussed     

Asymptotically convergent switching differentiator

A novel switching differentiator with a considerably simplified form is proposed. Under the assumption that the time‐derivative of a time‐varying signal has a Lipschitz constant, it is shown that estimation error is asymptotically convergent to zero. The estimated derivative shows neither chattering nor peaking phenomenon. A differentiator that estimates the first‐order derivative of a signal is first proposed, and, by connecting this differentiator in series, higher‐order derivatives also become available. Simulation results show that the proposed differentiator shows extreme performance improvements compared to the previously established widely used differentiators such as high‐gain observer or higher‐order sliding mode differentiator.