张韵琦.输电线路空载合闸暂态过程中的CT极性在线判别[J].电测与仪表,2021,58(1):62-68. Zhang Yunqi.On-line discrimination method of CT polarity during the transient process of no-load closing of transmission line[J].Electrical Measurement & Instrumentation,2021,58(1):62-68.
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
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.
