利用差动电流及支路序电流特征的母线CT断线识别及保护闭锁策略研究

Busbar CT Disconnection Identification and Protection Blocking Strategy Using Differential Current and Branch Sequence Current Characteristics

现有3/2接线母线的电流互感器(current transformer,CT)断线闭锁策略由于无法引入母线电压信息,某些场景下难以可靠区分CT断线与母线短路故障,存在将母线经高阻短路故障误判为CT断线、重负荷支路CT断线母线差动保护误动的问题。为此,不改变现有母线差动保护动作特性的基础上,文章充分利用母线差动电流及支路序电流的幅值和相位特征,提出一套高适应性的CT断线闭锁策略,避免因CT断线闭锁策略不当导致的母线保护不正确动作的问题。首先推导母线CT断线与母线短路故障时母线差动电流和支路序电流的特征,利用其在相位和幅值上的差异构造一套全新的CT断线识别判据,可实现无需电压信息的CT断线可靠识别,避免单一变量构成的过量保护整定困难的问题。此外,优化CT断线与母线保护间的动作逻辑,短路故障情况下,通过附加短路故障识别判据可实现短路故障后的母线保护快速开放。利用数字仿真系统(real time digital simulation system,RTDS)建立典型3/2接线的母线模型,大量仿真实验验证了CT断线识别判据及母线保护闭锁逻辑的可靠性。

The existing blocking strategy of the 3/2-connection busbar,when a CT disconnection occurs,cannot distinguish the CT disconnection with the busbar short-circuit fault in some scenarios due to its inaccessible of the voltage information,which may cause the problem of misjudging the high-resistance short-circuit fault as a CT disconnection,or a misoperation of the bus differential protection when the heavy-load branch CT is disconnected.Therefore,on the basis of not changing the operating characteristics of the existing bus differential protection,a set of highly adaptable CT disconnection blocking strategy is proposed by making full use of the amplitude and phase characteristics of the bus differential current and the branch sequence current,avoiding the problem of the incorrect operations of the busbar protection caused by the improper CT disconnection blocking strategy.Firstly,the characteristics of the bus differential current and the branch sequence current are deduced when the bus CT is disconnection and the bus is short-circuited.and a new set of CT disconnection identification criteria is proposed by using the difference in the phase and amplitude,which realizes the identification of the CT disconnection without any voltage information,avoiding the fixed value setting caused by a single variable.In addition,the action logic between the CT disconnection and the busbar protection is optimized.In the case of a short-circuit fault,the busbar protection can be quickly started through the additional short-circuit fault identification criterion.A typical busbar model of 3/2-connection is established in the RTDS,,and a large number of simulation experiments verified the reliability of the CT disconnection identification criterion and the busbar protection blocking logic.