Influence of Series Choke on Damping of Switching Transients in Distribution Transformers

Distribution transformers operating in modern system grids or in industrial networks are subjected to many switching transients,which may occur due to routine operations,network reconfigurations or as reaction on protection signals.Depending on the network configuration and parameters,such events may lead to external overvoltages and result in additional stresses on the insulation system.This paper presents the influence of a series choke on damping of switching transients in distribution transformers.The impact of the choke is assessed by both amplitude and rise time reduction.The suppression of the transient rise time is shown for a test configuration involving distribution transformers connected to low loss cable lines and a medium voltage breaker.Such phenomena are especially typical for industrial networks where switching operations are very frequent.Both simulation and experiment results are given.Simulation results as well as measurement results confirmed that switching events can lead to high dU/dt and in consequence,can have adverse impacts on insulation system.Voltage escalation during switching event is strongly related with system conditions.The results obtained for presented mitigation method are promising and indicate significant dU/dt reduction as well as number of ignitions and voltage peak value.The protection of distribution transformers with a series choke is a new approach dedicated to environments prone to the occurrence of transients with high steepness.Experimental results show that the application of serial choke with suitable parameters realizes the reduction of dU/dt at the machines terminal from 24 kV/μs to 5 kV/μs,as well as the reduction of voltage peak value from 10 kV to 5 kV.The number of ignitions is also reduced.

A Multi-Gap Multi-Channel Gas Switch for the Linear Transformer Driver

A multi-gap and multi-channel gas switch with convexo-convex discal planet electrodes was designed and investigated. Eight gaps are formed in series by a trigger electrode, six intermediate electrodes and two high voltage electrodes with a uniform gap length of 5 ram. The self breakdown and triggered breakdown performance of the switch are reported. Both the delay time and jitter decrease with the increase in the trigger voltage, switching coefficient and the decrease in the trigger isolating resistor. The delay time of the switch is about 40 ns, and the jitter is less than 2 ns when charged with 4-85 kV and triggered by a voltage pule of -75 kV. The inductance of the switch is about 30 nH.

Optical Diagnostics of Multi-Gap Gas Switches for Linear Transformer Drivers

The trigger characteristics of a multi-gap gas switch with double insulating layers,a square-groove electrode supporter and a UV pre-ionizing structure are investigated aided by a high sensitivity fiber-bundle array detector, a UV fiber detector, and a framing camera, in addition to standard electrical diagnostics. The fiber-bundle-array detector is used to track the turn-on sequence of each electrode gap at a timing precision of 0.6 ns. Each fiber bundle, including five fibers with different azimuth angles, aims at the whole emitting area of each electrode gap and is fed to a photomultiplier tube. The UV fiber detector with a spectrum response of 260-320 nm,including a fused-quartz fiber of 200 μm in diameter and a solar-blinded photomultiplier tube, is adopted to study the effect of UV pre-ionizing on trigger characteristics. The framing camera,with a capacity of 4 frames per shot and an exposure time of 5 ns, is employed to capture the evolution of channel arcs. Based on the turn-on light signal of each electrode gap, the breakdown delay is divided into statistical delay and formative delay. A decrease in both of them, a smaller switch jitter and more channel arcs are observed with lower gas pressure. An increase in trigger voltage can reduce the statistical delay and its jitter, while higher trigger voltage has a relatively small influence on the formative delay and the number of channel arcs. With the UV pre-ionizing structure at 0.24 MPa gas pressure and 60 kV trigger voltage, the statistical delay and its jitter can be reduced by 1.8 ns and 0.67 ns, while the formative delay and its jitter can only be reduced by 0.5 ns and 0.25 ns.

Tetragonal Domain Switching via Reversible tm Phase Transformation

Grinding-induced tm phase transformation and the resultant texture in ceria-yttria-doped tetragonal zirconia polycrystals with varied tetragonality have been studied by XRD. It is observed that the reversible tm phase transformation occurs during grinding and the intensity ratio of I(002)t/I(200)t increases with the transformability. The author proposes that the texture induced by grinding at low temperatures is due to the tetragonal variant reorientation via cyclic,reversible tm phase transformation, termed 'transformational domain switching', instead of the ferroelastic one

Research of a fractional-turn ratio saturable pulse transformer and its application in a microsecond-range pulse modulator

As a combination device for a step-up pulse transformer and a magnetic switch,the saturable pulse transformer is widely used in pulsed-power and plasma technology.A fractional-turn ratio saturable pulse transformer is constructed and analyzed in this paper.Preliminary experimental results show that if the primary energy storage capacitors are charged to 300 V,an output voltage of about 19 kV can be obtained across the capacitor connected to the secondary windings of a fractional-tum ratio saturable pulse transformer.Theoretical and experimental results reveal that this kind of pulse transformer is not only able to integrate a step-up transformer and a magnetic switch into one device,but can also lower the saturable inductance of its secondary windings,thus leading to the relatively high step-up ratio of the pulse transformer.Meanwhile,the application of the fractional-turn ratio saturable pulse transformer in a μs range pulse modulator as a voltage step-up device and main switch is also included in this paper.The demonstrated experiments display that an output voltage with an amplitude of about 29 kV,and a 1.6 μs pulse width can be obtained across a 3500 Ω resistive load,based on a pulse modulator,if the primary energy storage capacitors are charged to 300 V.This compact fractional-turn ratio saturable pulse transformer can be applied in many other fields such as surface treatment,corona plasma generation and dielectric barrier discharge.

Design and FPGA implementation of multi-wing chaotic switched systems based on a quadratic transformation

Based on a quadratic transformation and a switching function,a novel multi-wing chaotic switched system is proposed.First,a 4-wing chaotic system is constructed from a 2-wing chaotic system on the basis of a quadratic transformation.Then,a switching function is designed and by adjusting the switching function,the number and the distribution of the saddle-focus equilibrium points of the switched system can be regulated.Thus,a set of chaotic switched systems,which can produce 6-to-8-12-16-wing attractors,are generated.The Lyapunov exponent spectra,bifurcation diagrams,and Poincarémaps are given to verify the existence of the chaotic attractors.Besides,the digital circuit of the multi-wing chaotic switched system is designed by using the Verilog HDL fixed-point algorithm and the state machine control.Finally,the multi-wing chaotic attractors are demonstrated via FPGA platform.The experimental results show that the number of the wings of the chaotic attractors can be expanded more effectively with the combination of the quadratic transformation and the switching function methods.

Regime switching模型下的幂式期权定价（英文）

研究了标的资产价格过程服从马尔科夫调节的几何布朗运动时的欧式幂型看涨期权的定价问题.特别是,市场利率,标的风险资产的预期收益率与波动率随着马尔科夫链的状态转移而变化.由于市场不完备,通过采用regime switching Esscher变换得到一个等价鞅测度并给出期权的定价公式.最后,考虑了所得结果的数值分析.

Effect of Switching Devices on Power Quality and Transient Voltage Suppression Using Capacitor Bank Model

The main purpose of the electrical power system is to transport and distribute energy generated by the central power plants in a safe and reliable manner to the customer premises. Most of the electrical equipment is exposed within the open which suggests they can be vulnerable to lightning strikes, road dwindling, windstorms, and a few engineering activities with the potential of causing different degrees of damage to the electrical equipment. One of the ways to guard the equipment is to deploy switching devices. However, the operations of most of these switching devices produce oscillatory transient in the electrical transmission and distribution systems which result in voltage, current, and frequency fluctuations in the load. This paper investigates the effect of switching devices on power quality and proposes a positive sequence voltage power transient suppression technique that can spontaneously improve the distorted voltage at the instant of capacitor switching using the capacitor line model as a case study. MATLAB/Simulink software was utilized for the analysis on an electrical network model with bus voltages of 69 kV/12.47 kV and 480 V. The results showed that, during switching operations, the positive sequence voltage power detector block produces ripple-free accurate results.

CSR Pulsed Switching Power Supplies

In 2001, CSR power supply system made a great progress. Three prototypes were designed for CSR quadruple and correct magnet. Three different companies provided the three prototypes, but the same circuit-chopper were employed. The simplified diagram is showed in Fig.1. All pulsed switching power supply prototypes were tested successfully before the end of 2001.

Design and Construction of Compact Repetitive Nanosecond Pulse Generator Based on Tesla Transformer

A compact high-voltage repetitive nanosecond pulse generator(HRNPG)was developed for studying the technology of repetitive nanosecond pulse technology and its related application.The HRNPG mainly consists of a repetitive charging module,a Tesla transformer and a sharpening switch.With its voltage lower than 1 kV,the primary repetitive charging circuit comprises two fast thyristors as its low-voltage switches.The spiral Tesla transformer acts as the main step-up component,and its peak transformation ratio is designed to be more than 100.A self-breakdown spark switch,i.e.the sharpening switch,is used to sharpen the output of the transformer and to generate nanosecond pulses.The HRNPG prototype is capable of generating pulses of 100 kV in peak with rise time 30 ns and the maximum repetition rate of 500 Hz on a 6 k load.Experimental results show,without any magnetic core,the developed Tesla transformer prototype can easily output high voltage while keeping itself small in size and light in weight,which is of significance for the compactness and portability of the pulse generator.The N2-insulated spark switch operated well at voltage close to 100 kV and the repetition rate within several hundreds of hertz.

NOVEL LINEAR TRANSFORMATION SWITCHED-CAPACITOR FILTER DESIGN

This paper presents a novel method that is applied to realize the Linear Transformation(LT)Switched-Capacitor Filter(SCF).It adopts the Voltage Control Voltage Source(VCVS)equalized transfor-mation to revise the original LC ladder filter and induce it into 16 basic sections and then extend the princi-ple of the LT in order to fit active and 3 port networks and give out switched-capacitor circuits corre-sponding to the 16 basic sections,which can realize all four kinds of filters——LP,HP,BP,BS filters.De-signed examples are given here.An Nth order filter only requires N amplifiers and the circuit is insensitive toparasitic capacitances.The experimental results of a 3rd order elliptic LP and a 6th order elliptic BP are giv-en and agree with the theory.

断路器选相投切系统在换流站中的应用研究

在换流站滤波器组及换流变压器配置断路器选相投切系统,可改善断路器开合暂态过程,在取消合闸电阻工况下仍可避免对电力设备及系统造成冲击。基于多个换流站选相投切工程实施及调试经验,进行了换流站选相投切系统应用的调查。介绍了选相投切系统构成、选相投切要求、断路器配套及预测试方法等。重点针对滤波器组、换流变压器的选相投切应用,总结了控制策略、选相投切系统带电冲击试验,及工程使用中需重点关注的问题、设备运维要求等,为相关技术人员提供参考。试点工程在特高压断路器中创新性地采用取消合闸电阻、增设选相合闸的专项改造方案。断路器选相投切系统总体运行效果良好,为技术的推广积累了工程运行经验。

一种针对驻留转换雷达的信号分选算法

复杂电磁环境下驻留转换雷达的信号分选是制约电子侦察技术发展的瓶颈,由于其复杂多变的成形规律,信号子周期难以被检测;脉冲重复周期调制类型不明,脉冲序列无法成功提取;提取的多个子周期脉冲序列无法合并为一部雷达信号,造成虚警。针对以上问题,提出一种针对驻留转换雷达的信号分选算法,利用双门限提高子周期检测概率,通过霍夫变换结合迭代自组织聚类判断信号是否属于驻留转换雷达,改进搜索算法以提取脉冲序列,依据排列熵指标将多脉冲序列合并为一部驻留转换雷达信号。仿真实验结果表明,所提算法在25%脉冲丢失率的复杂电磁环境下,可以将三部驻留转换雷达信号成功分选。

支路开关自放电对大型多路并联FLTD脉冲源可靠性的影响

快脉冲直线型变压器驱动源(fast linear transformer driver,FLTD)是建设下一代大型Z箍缩装置最有前景的技术路线之一。大型FLTD脉冲源中数以万计气体开关的可靠运行是提高Z箍缩装置可靠性的重要因素。该文基于15 MAZ箍缩科学实验装置的FLTD脉冲源设计,采用Monte-Carlo方法建立考虑支路开关自放电及其载荷共享效应的FLTD脉冲源可靠性计算模型,分析开关故障模式及其触发策略对脉冲源可靠性的影响。结果表明,主支路开关自放电产生的故障电压会引起开关级联自放电,降低装置可靠性。若主支路开关工作系数设定在0.5~0.7范围内,FLTD脉冲源故障率可低于1×10^(-4)。此外,触发器及触发支路开关的高可靠性对于提升脉冲源可靠性至关重要,增加触发器脉冲数量、降低触发器自放电故障率能够有效提升脉冲源可靠性,当触发器脉冲数量提升至4倍后,FLTD脉冲源故障率有望降低至1×10^(-5)以下。研究结果为大型FLTD脉冲源的开关工作系数及触发策略的选取提供参考,具有重要的工程应用价值。

一种新型分体式换流变压器有载分接开关

近年来发生了数起换流变压器有载分接开关在档位调节过程中爆炸起火的严重事故。针对此问题,提出了一种新型分体式换流变有载分接开关的设计方案,将切换开关部分与变压器本体分离,有效避免分接开关故障影响的扩大。切换开关各触头由真空永磁开关替代且操作机构独立配置,结合内部支路配置的电流采样装置,实现切换过程的监测可控。提出了分体式同步控制逻辑和切换开关分步控制逻辑,实现了分接开关调档过程的状态监测及故障保护。样机的试验结果验证了分体式换流变压器有载分接开关方案的可行性和有效性。

基于等效励磁电感的SiC串联器件型中压双有源桥变换器的软开关技术

基于SiC串联器件的双有源桥变换器因具有开关损耗小、功率密度高、能量控制简单等优势,有望成为中压变换场景中实现高频隔离的优选方案。为保证SiC串联器件的可靠均压,各器件上并联大容值缓冲电容,然而该设计使变换器在传输功率较低时难以实现零电压开通,严重影响变换器的整体效率和串联器件的可靠运行。该文通过构建SiC串联器件型中压双有源桥变换器多模态运行模型并深入分析其运行特性,提出一种基于等效励磁电感的无源软开关技术。所提技术可通过优化外接传输电感位置的方式实现中压侧等效励磁电感参数调节,从而在无额外控制前提下实现SiC串联器件的软开关范围扩展。最后,设计了4 kV/1 kV实验样机,实现了100 kW下运行。实验结果显示,所提出的软开关技术能显著地扩展变换器中SiC串联器件的软开关范围,在保证SiC串联器件均压稳定性的同时能够大幅降低变换器在轻载运行时的功耗。

超快光纤激光器中可控脉冲产生与湮灭动力学

本文采用实时傅里叶变换光谱探测技术,研究了基于泵浦强度调制的超快光纤激光器中锁模脉冲产生与湮灭动力学过程.结果表明:当泵浦调制电压处于高电平时,激光器输出稳定的锁模脉冲.随着调制电压跳变至低电平,锁模脉冲的强度不断降低,而后经历一段衰减振荡阶段后发生湮灭,在~5μs后孤子从噪声中重建,这一过程伴随着调Q不稳定性的产生.在低电平阶段,激光腔内的湮灭过程连续发生,其周期为~55μs.通过改变调制泵浦的占空比,能够操控在低电平调制下孤子连续湮灭的次数.进一步,锁模与孤子湮灭的连续切换过程与泵浦调制频率有关,调制频率的升高能够有效缩短两种状态的持续时间从而减少孤子湮灭的次数.此外,通过减小低电平的值,能够降低激光腔内的增益,使得孤子连续湮灭的周期缩短.研究结果有利于深入了解孤子的形成与湮灭动力学,并为超快激光器各种运行机制的发展提供了新的视角.

用Topswitch芯片设计的反激式开关电源

Topswitch系列芯片是PowerIntegration公司生产的开关电源专用集成电路 ,它将脉宽调制电路 (PWM )与高压MOSFET开关管及驱动电路等集成在一起。使用该芯片设计的小功率开关电源 ,可大大减少外围电路 ,降低成本 ,提高可靠性。本文介绍了Topswitch系列芯片的工作原理及用该芯片制作的 3 0W反激式开关电源 。