输电线路空载合闸暂态过程中的CT极性在线判别

On-line discrimination method of CT polarity during the transient process of no-load closing of transmission line

为避免输电线路投运后出现CT极性接反的错误,提出了一种输电线路空载合闸的暂态过程中在线判别CT极性的方法。建立单相输电线路空载合闸过程的物理模型,根据各电气量与线路参数的数学关系列写微分方程。将线路的电感或电阻视为未知量,求解微分方程,并分析在CT不同的极性状态下线路参数计算值的特点。将其计算值做归一化处理,以使该判别方法适用于不同的输电线路。为量化线路参数归一化等效值的分布规律,定义正向和反向系数。根据二者的比值可以识别出单相系统中CT的极性。基于单相系统的判别方法,结合三相电流之间满足的数学关系和不同形式的相模变换逆矩阵的特点,可识别出三相系统中各相CT的极性。在PSCAD中通过仿真验证了该方法的有效性。

In order to avoid the error of CT polarity inversion since the transmission lines have been put into operation,an on-line discrimination method during the transient process of no-load closing of transmission line is proposed in this paper.The physical model no-load closing for the single-phase transmission line is established firstly,and the mathematical relationship between electrical quantities and line parameters during closing process is described by differential equations.Line parameters such as the inductance or resistance are regarded as unknown quantities,and the characteristics of their values are analyzed when solving the differential equations under different CT polarities.Then,the calculation values are normalized,so that the discrimination method is applicable to different transmission lines.In order to quantify the distribution characteristics of normalized equivalent values,the forward and backward coefficients are defined.According to the ratio of these two coefficients,CT polarity in single-phase system can be discriminated.On this basis,combined with the mathematical relationship among the three-phase currents and the characteristics of phase-mode transformation inverse matrixes in different forms,the polarities of CTs in three-phase system can be identified.Finally,the effectiveness of the method is verified by simulation in PSCAD.