Analysis on the fault characteristics of three-phase short-circuit for half-wavelength AC transmission lines

Half-wavelength AC transmission(HWACT) is an ultra-long distance AC transmission technology, whose electrical distance is close to half-wavelength at the system power frequency. It is very important for the construction and operation of HWACT to analyze its fault features and corresponding protection technology. In this paper, the steady-state voltage and current characteristics of the bus bar and fault point and the steady-state overvoltage distribution along the line will be analyzed when a three-phase symmetrical short-circuit fault occurs on an HWACT line. On this basis, the threephase fault characteristics for longer transmission lines are also studied.

Steady-state Voltage Reactive Compensation Method for Half-wavelength Transmission Lines Considering Equivalent Power Supply Impedance

Half-wavelength AC transmission(HWACT)refers to transmission along lines with an electrical distance of half the power frequency wavelength.The voltage amplitude at the sending terminal is equal to that at the receiving terminal in steady-state.Furthermore,the voltage at the receiving terminal does not vary with load.However,the electrical distance has been extended in actual HWACT lines because of the impact of the equivalent power supply impedance,so the attractive characteristics no longer hold.As a result,reactive power compensation methods with constant power factor and constant voltage are needed and these are presented in this paper.The steady-state operational characteristics,the calculation methods of additional reactive power compensation and the admittance of a controllable shunt reactor are also given.The methods proposed in this paper are relatively simple to implement,and the calculations involved are straightforward,resulting in effective voltage stabilization.The results indicate that such compensation methods can increase the transmission capacity while maintaining a relatively low voltage along the line.

Integrated protection based on multifrequency domain information for UHV half-wavelength AC transmission line

Half-wavelength AC Transmission(HWACT)can improve capability of AC transmission significantly.According to the basic principle of HWACT,the electromagnetic transient model of HWACT is built to analyze the fault transient process of transmission line.Based on fault characteristics of HWACT,the adaptability of traditional protections for transmission lines is analyzed briefly,such as current differential protection,distance protection and over current protection.In order to solve the problems of conventional protection caused by HWACT,a novel integrated protection based on multi-frequency domain information is proposed in this paper,which uses both the power frequency information and transient information.The integrated protection based on multi-frequency domain information takes advantages of power frequency and transient protections,which can not only improve the performance of traditional protection of AC transmission line but also realize fast fault judgment by transient travelling wave protection.

Penetrating power characteristics of half-wavelength AC transmission in point-to-grid system

With the proposed concept of global energy interconnection, half-wavelength alternating current transmission(HWACT) technology becomes of more interest.HWACT lines can be adopted to establish a pointto-grid system, in which the penetrating power(PP) is produced between receiving terminals, having a significant effect on the power flow distribution.In order to investigate this phenomenon, the PP characteristics of the HWACT system are researched in this paper.First, the mathematical relationship between the transmission power and terminal bus voltages of a single HWACT line is derived using the equations of a distributed parameter model.The research indicates that the relationship between power and terminal voltages shows ‘‘reverse characteristics"opposite to those of regular short transmission lines.Then, the concept and definition of PP in a point-to-grid system with two receiving terminals are proposed, and the corresponding relationship between PP and the terminal bus voltages is derived.Simulations are carried out to validate the theory under different conditions, so that the accuracy and adaptiveness of the theoretical analysis can be proved.In addition, the results demonstrate that selecting the location for a HWACT system has demanding requirements in order to control the value of PP.

特高压半波长交流输电系统经济性与可靠性评估

结合特高压交直流输电技术经济性方面的最新研究成果,采用最小年费用法对特高压半波长交流输电系统和±800 kV特高压直流输电系统2种输电方案的经济性进行方案比较和敏感性分析,给出了特高压半波长交流输电系统的临界经济输送功率和附加控制费用上限,并对特高压半波长交流输电系统和±1 000 kV特高压直流输电系统的输电经济性进行了比较。运用可靠性评估方法对特高压半波长交流输电系统和±800 kV特高压直流输电系统2种输电方案进行了定性和定量的可靠性评估。

特高压半波长交流输电线路稳态特性研究

基于特高压半波长交流输电系统的正弦稳态解析解,分析了系统接感性负载和容性负载2种情况下,负载特性、功率因数对稳态运行特性的影响。结果表明:在不出现严重过载的正常工况下,半波长交流输电系统的线路过电压水平较低,线路损耗和电晕损耗较低,送端和受端的电压和电流的有效值差很小,相位基本反相;在过载情况下,线路中间段出现过电压现象;负载功率因数越高,线路的电压和电流越稳定。

特高压半波长输电线路潜供电弧抑制措施研究

潜供电弧是发展特高压半波长输电技术面临解决的关键问题之一。文中首先采用分段法建立了基于分布参数的潜供电弧数学模型,分析快速接地开关(high speed grounding switch,HSGS)对半波长输电线路潜供电弧的抑制作用;其次,建立半波长输电线路电磁暂态模型,分析快速接地开关限制因素对抑制效果的影响;最后,给出了快速接地开关沿线非均匀配置方法,获得了较优的快速接地开关配置方法。研究表明:HSGS投入时间对潜供电流抑制效果影响不大,为保留足够的时间裕度,应取值150 ms。HSGS接地电阻对潜供电流抑制效果影响较大,应小于1.5Ω。半波长输电线路采用沿线非均匀9组HSGS的配置方法,可有效抑制其潜供电流。

基于MMC的半波长交流输电潜供电流抑制措施研究

半波长交流输电技术因其自身的特点在远距离输电场景中提供了一种解决方案,然而潜供电流的问题限制了半波长交流输电技术的发展和应用,现有的潜供电流抑制方案在半波长输电系统中应用时均存在不足。为了解决这一问题,总结了潜供电流的分布规律,在此基础上,提出了基于模块化多电平换流器(MMC)的潜供电流抑制措施,并进行了控制策略的设计以及参数的选取。此外,提出了分相投切无源元件来配合MMC工作从而减少MMC容量的方案。最后,在仿真平台对所提抑制措施进行了仿真验证,结果表明该措施可以有效地抑制半波长交流输电的潜供电流,加快熄弧速度,提高系统的故障恢复效率。

变频变压器在半波长变频调谐的应用

针对半波长交流输电(HWACT)线路的调谐问题,本文提出了基于变频变压器(VFT)的变频柔性调谐装置来获得不同的运行频率,使得输电线路满足半波长交流输电的特性。本文论述了变频调谐和变频变压器各自的工作原理,在PSCAD/EMTDC中建立了基于VFT的半波长交流输电变频柔性调谐等值系统模型,并设计出相应的控制策略。对输电线路的电气距离小于和大于半个基频波长的情况分别进行算例分析,仿真结果证明了所述变频调谐方法和变频变压器的实施应用均是有效的。