线路纵差保护CT二次断线判据分析

Analysis of second loop break criterion of CT used in differential protection of transmission line

电流差动保护为了提高安全性一般都有CT二次断线判据,以区分内部故障和CT二次断线,并根据判据的结果决定是闭锁还是开放保护,因此CT二次断线判据可能影响线路差动保护正确动作。从弱馈系统、单侧电源、高阻接地等多个角度探讨CT二次断线判据对线路差动保护的影响,并在此基础上论证了引入两侧电压突变检测的必要性。分析表明,两侧电压突变检测CT断线判据可以较有效地减少CT断线检测判据对线路差动保护灵敏度的影响,提高保护装置的整体性能。

To enhance system security, there are CT＇s second loop break criterions, being expected to distinguish between internal fault and CT＇s second loop break, irr a transmission line differential protection commonly. Moreover, whether locking or opening the differential protection may depend on the judgement of this criterion. Thus CT＇s second loop break criterion can affect the performance of transmission line differential protection. The influence of CT＇s second loop break criterion on transmission line differential protection is discussed on several conditions, such as weak power feeder, line of one-terminal power supply, high resistance grounding fault etc. Then it is demonstrated why voltage change detection of two terminals is adopted in the criterion. The study indicates that the influence of CT＇s second loop break criterion upon transmission line differential protection is weakened greatly by using the criterion based on voltage change detection of two terminals and the protection performance is improved.