基于瞬时电流特征的电流互感器饱和识别改进方法

摘要

电力系统发生区外故障时电流互感器饱和可能引起差动保护误动,常用的解决方法选取的开放差动保护门槛值固定,未考虑差动电流畸变程度的影响,在饱和程度较轻时门槛值偏大,使得开放保护延时较大.针对这一问题,提出了一种基于瞬时电流特征的电流互感器饱和识别的方法.该方法在虚拟制动电流识别电流互感器饱和的基础上,通过分析电流互感器的传变特性得到电流互感器饱和程度与一次电流及其导数的关系,利用BP神经网络拟合算法建立一次电流特征与最优门槛值之间的映射关系,从而可以自适应选取开放差动保护门槛值,以减少差动保护闭锁时间.仿真结果验证了所提方法的有效性.%The CT(Current Transformer) saturation may lead to the misoperation of differential protection when external fault occurs in power system.The common solutions select the fixed threshold to unblock the differential protection and ignore the effect of the differential current distortion degree,so the threshold is larger under the less saturation degree,which causes longer protection delay.In order to solve this problem,a method based on transient current characteristics is proposed to identify CT saturation.Based on the identification of CT saturation by constructed restraint current,the CT transfer characteristics are analyzed to obtain the relationship among the CT saturation,primary current and its differential coefficient.The mapping relationship between the primary current characteristics and optimal threshold is established by BP neural network,and the threshold to unblock the differential protection is adaptively obtained to reduce the protection blocking time.The simulative results verify the effectiveness of the proposed method.