基于空充暂态电流的线路保护CT极性校验方法

线路保护电流互感器(current transformer, CT)二次采样回路接线正确是保护正确动作的前提。针对线路投运启动过程中保护CT极性校验困难的问题，首先分析了在有限负荷和无负荷下利用线路稳态电流进行极性校验的边界限制条件。进而针对不满足限制条件下无负荷极性校验困难的问题，提出了一种基于空充暂态电流的线路保护CT极性校验方法。该方法先利用幅值较大的本端暂态电流对三相CT相对极性进行初判，再通过线路本端暂态电流和测量电压基于线路结构计算对端暂态电流来实现本端保护CT极性错误相识别，CT极性正确时对端计算电流理论上为零，CT极性错误时会呈现较大的幅值。该方法有效解决了传统极性校验方法在负荷不足时无法校验的问题。仿真和录波验证了该方法的有效性，并已纳入工程应用方案。

CT polarity checking method for line protection based on no-load charging transient current

The correct wiring of a line protection current transformer (CT) secondary sampling circuit is a precondition for correct protection operation. There is difficulty in polarity checking during the operation and start-up of the line. Thus the boundary limit condition of the polarity checking using the steady-state current of the line under limited load and no-load is first analyzed. There is also difficulty of no-load polarity checking when the condition is not met. For this a CT polarity checking method for line protection based on no-load charging transient current is proposed. The CT relative polarity of three phases is preliminarily checked by the local transient current with large amplitude. Then, the transient current of the opposite terminal is calculated based on the measured value of the local terminal and the Bergeron line model to determine the phase with the wrong polarity of the local terminal. When the CT polarity is correct, the calculated current of the opposite terminal is theoretically zero. If not, it will have a large amplitude. The problem that the traditional method cannot take effect when the load is insufficient is solved by the proposed method. The effectiveness of the method is verified by simulation and wave recording. This has been incorporated into the engineering application scheme.