This paper introduces the eigensystem realization (ER)-based identification algorithm and the Z-domain method (ZDM) to improve the impedance estimation of transmission lines under fault conditions, which is achieved by removing the exponential decaying DC offset from current signals in distance relays. Both methods effectively work employing a one-cycle rectangular window; specifically, the Z-domain method works in less than a fifth of one-cycle window, ensuring timely, accurate, and prompt estimates. To confirm the effectiveness and performance of the proposed algorithms, they are evaluated under steady-state and dynamic conditions by using time-domain simulations performed in PSCAD©and DIgSILENT©PowerFactory. They also are compared with the well-known discrete Fourier transform (DFT). The attained results indicate that both the ER-based and Z-domain methods can become a powerful tool to reduce the adverse influence of exponentially decaying DC offsets in distance relays.

本文介绍了基于特征系统实现（ER）的识别算法和Z域方法（ZDM），以改善故障条件下传输线的阻抗估计，这是通过消除距离继电器中电流信号的指数衰减DC偏移实现的。两种方法都有效地使用了一个周期的矩形窗口。具体来说，Z域方法的工作时间不到一个周期的五分之一，从而确保了及时，准确和迅速的估算。为了确认所提出算法的有效性和性能，通过在PSCAD©和DIgSILENT©PowerFactory中进行的时域仿真，在稳态和动态条件下对它们进行了评估。还将它们与众所周知的离散傅里叶变换（DFT）进行比较。