电网第三道防线问题分析及失步解列
摘要：三道防线是电力系统安全防御体系的重要组成部分，第一道是继电保护系统，第二道是包括稳控装置及切机、切负荷等措施在内的电力系统安全稳定控制系统，第三道由失步解列、频率及电压紧急控制装置构成。

鉴于目前第三道防线尚存漏洞或不足，分析了振荡中心转移至主网内部、故障点切除不掉引起远后备保护无选择动作、重要联络线的相继开断造成的潮流大转移引起受端系统电压不稳定、距离保护三段在线路严重过载时误动作引起的连锁反应及大机组保护装置参数与电网不协调引发的事故等五种情况。

针对这些情况提出了若干解决的对策，特别是研究和提出了构建互联电网的综合解列控制系统的方案，解决了振荡中心转移到主网内部时能及时采取解列等优化措施，解决了电压不稳定事故发生前隔离故障区域或将难以控制的电压崩溃事故转化为
容易解决的频率稳定问题等，这些对策可显著增强电网的第三道防线。

关键词：电力系统安全；三道防线；失步振荡；综合解列系统
Analysis on the Problems about the Third Defense Line of Power Systems and the Concept of Dealing with the Separation Relay after Loss of
Synchronism
Abstract：“Three Defence Lines”is a concept of the whole security defence system for power systems being used for a long time but clearly defined in this paper as follows: the first is the protection relay system; the second line the stability and security control including generator rejection and load shielding and the third line the separation relay after loss of synchronism followed by the frequency and the voltage emergency control. The paper argues that there exist indentation and deficiency in the third line and analyzes in detail the following five scenarios.
a) After tripping of some major tie lines the oscillation centre may shift into the main part of the power system. b) The remote/reserve protection relay may malfunction caused by the delays of fault tripping. c) Voltage instability of the receiving power systems caused by the power flow redistribution after the tripping of major transmission lines. d) Cascading process caused by the serious overloading after the malfunction of the third stage of the distance relay. e) The malfunction of the protection relay of major generator units caused by the incorrect coordination of the protection settings. To these problems countermeasures are proposed. Especially, the construction of a scheme of the synthesized separation control of the interconnected power system is studied and presented which can perform the optimal separation of faulty areas before the voltage instability occurs, or it may transfer the voltage instability problem that is difficult to remedy into the frequency instability that is relatively easy to remedy. This proposal will significantly improve the effectiveness of the third defence line of the special protection scheme of system stability and security.
Key words： power system security; three defence lines; oscillation; synthesized separation control system。