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特高压输电线路方向纵联保护
Pilot Protection of Ultra-High-Voltage Transmission Lines with Directional Comparision
【作者】 薛士敏；
【作者基本信息】 天津大学 ， 电力系统及其自动化， 2008， 博士
【摘要】 国家电网公司晋东南一南阳一荆门交流1000kV特高压输电示范工程已经动工,这填补了我国百万伏电压等级的空白,是我国电网技术发展新的里程碑。特高压输电线路将成为我国电网的骨架,保证特高压输电线路安全、可靠运行对于整个电网有重要意义。因此,研究适用于特高压输电线路的继电保护原理是摆在我们面前的一项紧迫任务。本文正是针对特高压输电线分布电容大、非周期分量衰减速度慢和高频分量丰富的特点,研究了适用于特高压输电线路方向纵联保护原理,最终提出了一套适用于特高压输电线路的主保护配置方案。针对负序方向元件,提出了适用于特高压输电线路的保护动作逻辑方案,给出了各种故障情况下保护的动作逻辑。采用数字式二阶RC低通滤波器结合小矢量算法和相模变换可在几个毫秒内快速求得负序电压、电流及其功率方向,用该方法实现的负序方向元件不但能正确反应各种不对称短路,还能正确反应短路瞬间只有5ms不对称状态的三相短路故障。通过对我国正在建设和未来更长的1000kV特高压输电线的仿真研究,证明了这一方法的正确性。提出了基于分布参数输电线路模型的新的补偿算法,消除了线路分布电容对负序方向元件的影响,该补偿算法对故障暂态和故障稳态具有同样的补偿效果。提出了新的适用于特高压输电线路的故障分量分相补偿式方向元件,该方向元件本身具有选相功能,无需配合选相元件,可反应全相及非全相运行情况下的各种故障。通过理论推导得出从初始行波到稳态行波过渡过程的数学公式,统一了不同阶段的故障分量信号;定义了初始行波的概念,并指出了其持续时间的影响因素,针对末端含有储能元件系统,从物理和数学两方面剖析了初始行波的功率极性;通过分析提出反射系数是时变函数,给出了在不同暂态阶段行波反射系数的变化范围。提出了适用于同杆双回输电线路的新的方向纵联保护原理。该原理利用同序负序分量实现方向比较,将双回输电线看作一个被保护单元,消除了原有基于每一回线的方向元件在双回线非同名相跨线故障时受双回线线间互感影响需将保护闭锁的缺点。
【Abstract】 China State Grid Corporation is beginning to build a Ultra-high voltagetransmission line from southeast shan-xi province to Jing-men of Hu-bei province.This project is a new milestone in history of china power grid development. It willserve as strongbackboneof Chinapower system andhas veryimportant significancein enhancing the reliability and stability of system operation. Cautious selection oftheprotectionschemeforUHVtransmissionlines is animportant task ofcolleagueworkinginfieldof protectiverelaying.UHV transmission lines have large distributed capacitance, decaying slowlynon-periodic component and rich high frequency components. Based on thecharacteristics of UHV transmission lines, pilot protection with directionalcomparision for UHV transmission lines and a main protection scheme forUHVtransmissionlines were studiedinthis paper.Against negative sequence directional components, logic block diagram ofultra-high voltage transmission line protection and under various fault conditions thelogic of protection action are given. Digital Second-order RC low-pass filter withphaselet-based algorithm and phase-mode transformation, negative sequence voltage,current and power can be obtained quickly in a few milliseconds. This negativesequence directional protection using the proposed algorithm do not operate whenfault is in reverse direction, but it can reliablyact duringvarious internal asymmetricand symmetric faults. This algorithm can capture the beginning asymmetry of threephase short-circuit if the asymmetry only lasts 5ms. Simulations for the 1000 kVUHV transmission lines under construction in China proved the correctness of thisalgorithm .Based on the transmission line model with distribution parameters, a newcompensation algorithm was proposed in this paper. The compensation algorithmeliminates influence of the line distributed capacitance on the negative sequencedirectional protection. The compensation algorithm has the same effect both in thetransient process and steady-state process after faults occurrence.Segregated phase compensator type directional relay based on the faultcomponent was proposed. The relay can be applied to UHV transmission lines andhas the function of phase selection. It can respond to various fault under three phaseoperation conditionand twophaseoperation condition. Aformula which describes the transient process from beginning traveling waveto steadytraveling wave was deduced and the concept of initial traveling wave stagefirst was defined and its duration was given. It leads to a conclusion that reflectionfactor is a time dependent function, and variation range and reflection factor atdifferent stage were presented .Based on unified traveling wave theory andtransmission line model of reflective terminal with energy storage element , powerpolarity of initial traveling wave was analysed with both physical and mathematicalmethod.A new directional relay principle for parallel line on same towers has beenproposed inthis paper. Parallel lineonsametowers is regardedas oneprotectedunit.The directional relay is based on same directional negative sequencecomponents .Because of influence of mutual inductance, directional protection onsingle line has to be latched-up during cross line fault between different phases, thisshortcomingis eliminatedinthis newprinciple.