高压直流线路外文翻译.doc

1、.Analysis of the Line Protection for HVDC Power Transmission SystemsHVDC (High Voltage Direct Current) technology is making rapid progress. It has the characteristics as far transmission distance, large capacity and flexible control, etc. The transmission of power grid is now developed into a AC-DC

2、combination mode.HVDC transmission takes an increasingly important position in the long distance and high-power transmission project, for its large power of transmission, low cost and good performance advantages of control. It is regarded as the principal means of high-capacity, long-distance transm

3、ission and asynchronous networking in developed countries. In China, HVDC becomes hotter and hotter as the result of “Western Power to the East, North and South to Share Power, National-link Network” especially in the vigorous development of the state UHV in recent years. However, according to the o

4、peration of “GZB-SNQ and TSQ-GBJ HVDC project”, reliability of Circuit Protection Device of domestic and international HVDC lines is not high, within easily disoperation and other issues. So how to improve reliability of HVDC transmission lines is urgently needed to solve in our countrys development

5、 of HVDC.A large number of unnecessary HVDC outages are induced by the HVDC line faults because of the low level of sensitivity of HVDC line protections, leading to a significant negative influence on the safety of the power system. On the one hand, there is a lack of effective analytical theory and

6、 setting calculation method due to the complexity of HVDC line faults. It is difficult to reveal the underlying principle and the border of influencing factors just by the numerical simulation of the HVDC system. On the other hand, the transient characteristics of the HVDC line fault and thus the li

7、ne protections are affected by the HVDC control system, which is very complicated and still a hard nut to crush. In this paper, the analytical theory of the HVDC line fault, dynamic characteristics of the protections and the control system and their coordination are studied and an improved protectio

8、n scheme is proposed to meet the significant demand of the HVDC system, which is not only valuable in the academic area but also utility in the engineer field.The work is summarized as following:(1) Analytical treatment is applied to indicate the reflection principles at the fault position, between

9、the modal quantities and at the terminals of the HVDC line. Based on the distortionless line model, the analytical solutions of the traveling waves on both the monopole system and the bipolar system are developed to reveal effects of the smoothing reactor, DC filters, fault resistance on the traveli

10、ng waves caused by the line fault. It is shown that the wave-front of the voltage at the terminal is consist of a exponential decay component and a sinusoidal component and thus the amplitude and the derivative of the wave-front both attenuate, although the initial incident wave has a step waveform.

11、 The initial amplitude mainly depends on the fault resistance. Furthermore, the change rate of the voltage which is the dominating discriminant of the existing traveling wave protection can be obtained for setting calculation of the traveling wave protections of the HVDC line. The simulation results

12、 obtained from the EMTDC model of the real HVDC system shows the effectiveness and credibility of the setting method.(2) A novel protection principle based on the polarity comparison of modal back waves is proposed in the paper, which is effective to improve the capability of detecting the high resi

13、stance line faults. The threshold of the change rate of the traveling waves which is the dominating discriminant of the existing traveling wave protection must be greater than the ones caused by the external faults. Thus, the response of the existing traveling wave protections to the high resistance

14、 and the far distance line faults. The polarity comparison instead of amplitude comparison is used to improve sensitivity of the traveling wave protection. The simulation results based on the EMTDC show the effectiveness of the proposed protection principle.(3) The operation time of the existing DC

15、Line Differential Protection (DLDP) is too long as the blocking criterion cant distinguish the DC line fault from the AC system failure. A novel blocking criteria, according to different spectrum of the differential currents between the DC line fault and the AC system failure, is presented. Simulati

16、on results obtained by the EMTDC show that the proposed criteria can discriminate the line fault and the faults in the AC system availably and rarely affected by the fault impedance and the fault distance, while it does shorten the operation time of the DLDP.(4) The effect of the control system on t

17、he HVDC line faults is studied using the EMTDC model of real HVDC system. It is shown that the continuous fluctuation of HVDC line current may be induced by voltage adjusting function and transient current control function of the Voltage Dependent Current Limit (VDCL) at the rectifier, which leads t

18、o miss-trip of DLDP. For this issue, a criterion using the voltage of the commutation bus at the rectifier is proposed to avoid the unfavorable influence of the control system on the DLDP.(5) The dynamic characteristics of the Derivative and Under Voltage Protection (DUVP) is presented by means of t

19、he analysis of field data and the simulation results. The DUVP may mal-operate because of the harmonic distortion of DC voltage and in-coordination between the AC main protection and the DUVP when the cascading failure happens in the AC system. To address the problem, the DC current criteria is adde

20、d to the DUVP (6) A novel HVDC line protection scheme, based on the sampling frequency and channels of the existing HVDC line protection. A simulation system including both the existing scheme and the proposed one is developed based on the EMTDC models of an real HVDC system. The comparison of the t

21、wo schemes shows the validity of this papers effort.This work was supported by the National Natural Science Foundation of China (50337010) and the co-operative researches with China Southern Power Grid(CSG). Some of the results has been applied in the modification of the HVDC projects in CSG, which

22、shows effectiveness and credibility of this papers efforts.Tian-Guang, Gao-Zhao and Xing-An HVDC transmission system are all puzzled by the abnormal DC voltage fluctuation, and the reason is not very clear up today. In this paper,we can know that the differential protection will fail to action due t

23、o the current fluctuation caused by the control system.Based on the actual HVDC line parameters and the EMTDC simulation platform,the current DC line protection and the influence of the control system is evaluated,in connection with the fault records and the simulation results.An improvement scheme

24、is proposed.and it gave the corresponding modification and improvement in terms of the problems.高压直流线路保护分析直流输电技术的不断进步及其在大电网发展中体现出来的送电距离远、送电容量大、控制灵活等特点,使直流输电技术找到了发展空间,电网跨入了一个交直流互补的时代。高压直流输电以其传输功率大、线路造价低、控制性能好等优点，在远距离、大功率输电中占有越来越重要的地位，世界发达国家都把它作为大容量、远距离送电和异步联网的主要手段。我国也因“西电东送，南北互供，全国联网”，尤其是近年来国家大力发展特高压

25、，而使得高压直流输电成为电力建设的热点。然而根据葛上直流输电工程和天广直流输电工程的运行情况来看，目前国内外投运的直流线路继电保护装置普遍存在着可靠性不高，易误动等问题，因此如何提高直流输电线路保护的可靠性是我国发展直流输电亟待解决的问题。高压直流输电线路保护的正确动作率一直较低,大量直流线路故障是由直流控制系统响应动作,造成直流闭锁,引起不必要的直流停运,给电网安全运行带来重大影响。一方面由于直流线路故障本身的复杂性,目前缺乏有效的理论分析体系和保护整定校验方法,单纯依赖实际直流工程数值仿真系统的研究模式难以揭示深层机理和作用边界;另一方面,线路故障后直流线路保护的暂态响应特性与控制系统强相

26、关,而对直流系统这种特有复杂性对线路保护影响的研究较少。本文结合我国直流输电工程重大需求,在直流线路故障解析、控制保护动态响应特性与协调、保护新原理及方案改进等方面开展研究,选题具有重要的学术价值和工程实用意义。本文主要研究工作包括:1)在系统研究直流线路行波在故障点、模量间及线路末端的折反射规律的基础上,推导了基于无畸变传输线模型的单极和双极直流线路行波解析解,用以研究平波电抗器、直流滤波器、故障电阻等因素对直流线路行波的影响机理。研究表明:直流滤波器使行波波头由阶跃波变成衰减的振荡波,从而使其变化率和幅值都减小;过渡电阻和故障距离主要影响行波波头的幅值大小。基于实际直流工程的EMTDC仿真结果表明,本文提出的行波解析解可用于实际工程中的行波保护整定计算。2)提出了基于模量极性比较的单端行波保护新原理,有效地提高了直流线路行波保护耐受过渡电阻的能力。现有行波保护以行波波头变化率和变化幅度为判据,其定值必须大于区外故障引起的波头变化率以保证其选择性,制约了对过渡电阻和故障距离的反映能力。本文基于故障极线路与健全极线路反向行波的差异构成判据,以极性比较