【作者】 王玲；

【导师】 李振兴；

【作者基本信息】 三峡大学 ， 电气工程（专业学位）， 2018， 硕士

【摘要】 随着我国超/特高压、远距离、大容量输电的发展,串联电容补偿设备(简称串补)被广泛地应用到电力系统中。它在提高系统稳定性和传输能力等方面改善了电力系统的性能,但串补设备的引入,破坏了输电线路阻抗的均匀性。串补设备的电容特性一定程度上会使串补线路故障时出现“电流反向”的问题。随着电网规模的扩大、系统结构的复杂化,系统背侧等值阻抗减小,相对较高的串补容抗值,电流反向的几率进一步增大,从而引起电流差动保护拒动的风险越来越大。因此串补设备对区域电网系统线路保护的影响日益严重,使线路保护面临新的挑战。本文基于电流差动保护在反向中可能因灵敏度不足而拒动,开展串补设备对差动保护影响以及改进差动保护原理的研究,具体分为以下4个方面:(1)分析了含串补设备区域电网电流反向的特征及其界定条件。论述了串补设备导致的电流反向对不同线路保护原理影响的机理,为后续研究串补设备对线路差动保护的影响提供方法和理论基础,并结合实际工程模型,在EMTDC工程环境下,验证了电流反向出现的条件。(2)针对大串补线路区内故障拒动问题,提出了一种基于线路两端幅值和相角综合制动的差动保护新原理。分析了大串补线路差动保护区内故障时灵敏度降低的原因,并结合不同的串补度、过渡电阻、功角差等影响因素开展差动保护动作特性研究,研究发现,尽管电流出现反向,但其两端电流的相位并不一致,引入相角与电流幅值建立综合制动判据,来提高保护灵敏度。基于PSCAD软件的仿真结果显示改进的差动保护在区内故障出现电流反向时有效提高了灵敏度,且不影响其他故障条件下的可靠性。(3)针对多串补区域大电网,系统区内外故障极易出现电流反向,提出了一种改进的广域电流差动保护制动判据。基于传统广域差动保护的基本原理,从理论上对比分析了差动保护四种常规制动判据在面向区域大电网时的优缺点。进一步,面对保护区域电流反向特性,在不同的故障条件下,分析广域电流差动保护拒动的原因,区分广域制动电流的方向性,类比同向流进与同向流出为线路的两端电流,基于基尔霍夫电流定律借鉴改进电流差动保护原理的制动特性实现广域电流差动保护制动。仿真验证了上述改进方法的可靠性。(4)针对以上改进的广域差动保护判据,采用了动模实验进行仿真。更多还原

【Abstract】 With the development of high capacity and long distance in UHV and EHV transmission line,the series compensation device(SC for short)is widely applied to the power system.SC is favourable to the performance of the power system,for providing better transmission capability,increasing of the stability,etc.However the balance of the vectors in transmission line is destroyed by the introduction of SC equipment.The capacitive characteristic of SC may cause the problem like current inversion during fault incepted on such a compensated line to some extent.Furthermore,the risk of fault current reverse will be increasing during the line internal fault with the emergence of these phenomena that the scale expanding,the complex interconnection of power grid,the decrease of the system impedance in the back of the line and the relatively high capacitance impedance.In consequence,the failure of pilot current differential protection in series compensated line will be increasing.Therefore,the influence of SC on the line protection of regional power grid is becoming more and more serious,which makes the relay protection facing new challenges.Based on the principle that differential protection will fail to trip due to lack of sensitivity during current reversed,the effects of SC on line differential protection and the improved principle of differential protection are studied in this paper.It has following several aspects specifically.(1)The characteristics and defining conditions of the reverse current are analyzed for the regional power grid with SC equipment.How SC affects the operation characteristics of relaying with different principles is also discussed.It provides a theoretical principle and method for subsequent research about the influence of SC equipment on line differential protection.Combined with engineering models,the requirement for current inversion has been verified under the environment of EMTDC Engineering.(2)An improved criteria based on the current amplitudes and phases on both sides of series compensated lines are proposed to solve the misstrip of line current differential protection.The reason is analyzed for the reduction of sensitivity calculated by the differential protection at the internal fault.In addition,the operation characteristics of differential protection are studied by focusing on the multiple factors which include different series compensation,power angle difference and transition resistance etc.Research shows that the phases of the two ends of the protected line are not the same,even though the current is reversed.Thus,to improve the sensitivity of protection,the fault current amplitudes and phases are introduced to form a comprehensive restraint criterion.The simulation results based on PSCAD/EMTDC show that the protection sensitivity is obviously increased in the improvement scheme during fault current reversed when there is an internal fault on the line.The scheme has no effect on the reliability of other fault conditions too.(3)For the large power system with multiple series compensator,it’s very easy to appear current reverse during internal or external faults in the system.Therefore an improved braking characteristic of wide area current differential protection criterion is proposed.Based on the basic principle of the traditional wide area differential protection,the advantages and disadvantages of the four conventional braking criteria for differential protection in regional large grid system are compared and analyzed theoretically.Further,reasons are obtained about the misstrip of wide area current differential protection under different fault conditions through applying current reverse characteristics in the protected area.An implementation method based on restraint characteristic of wide area current differential protection is used to distinguish the direction of the wide area restraint current.According to Kirchhoff’s current law and learning from the improved restraint characteristics mentioned above,current flows in and flows out from the same direction are analogous to the current at both ends of the line.Based on PSCAD/EMTDC simulation method,this thesis validated the effectiveness of the related improved measurement.(4)To verify the improved criterion of wide area differential protection mentioned above,dynamic simulation is used to simulate.更多还原