母线保护电流互感器断线判据的分析及改进判据

Analysis of CT failure criterion in bus protection and its improved criterion

母线差动保护一般都配置电流互感器断线判断功能,以提高差动保护的可靠性。按照现有规范,当母线支路发生电流互感器二次断线时,需闭锁差动保护;当母联间隔电流互感器发生断线时,不闭锁差动保护。因此电流互感器断线判据的选择将影响母线差动保护的正确动作。从大负荷电流互感器断线、不完全电流互感器断线、高阻接地故障、单电源系统等多个角度分析现有母线电流互感器断线的判据存在的问题,并在此基础上提出了新的母线电流互感器断线判据:对于接入电压的母线保护,采用灵敏的电压判据作为辅助判据,对于无电压引入的母线保护,采用支路零序电流与差流的比值及差值作为辅助判据。试验结果表明,所提判据能够准确有效地识别电流互感器断线与故障,当发生电流互感器断线时,可靠闭锁差动保护,而当母线发生故障时,不会影响差动保护的快速性。

The CT（ Current Transformer） failure detection function is configured in the bus differential protection to improve its reliability. According to the existing specification, the differential protection should be blocked during the CT secondary breakage of the bus branch while not he blocked during the CT secondary breakage of the bus tie bay. So the CT failure detection has influence on the correct operation of bus protection. The disadvantage of the existing CT failure criterion is analyzed in the aspect of the heavy load CT failure, incomplete CT failure, grounding fault with high resistance and power system with single power source, based on which, the improved criterions are proposed：the sensitive voltage is adopted as an auxiliary criterion for the bus protection with voltage blocking, and the ratio of branch zero-sequence current to the differential current and the difference value between them are adopted as auxi- liary criterions for the bus protection without voltage blocking. The simulative results show that the improved crite- rions can distinguish the CT failures and faults accurately and effectively, the differential protection will be reliably blocked when CT failure occurs, and the speed of differential protection won＇t be affected when the bus fault occurs.