A parameter estimation method for untransposed transmission lines considering parameter identifiability under different internal faults

This paper proposes a method to estimate parameters of untransposed transmission lines under different internal fault conditions. By employing a nonlinear least square approach combined with a multi-initialization strategy, the method achieves accurate estimation of line impedance parameters, particularly the inductive component, under low-resistance fault conditions. The core contribution of this work lies in revealing the distinct parameter identifiability, which is strongly dependent on the internal fault type and evaluating the sensitivity of different line parameters by using the proposed sensitivity formula. Specifically, the study demonstrates that only fault types involving the spatially special phase of the untransposed line exhibit enhanced parameter identifiability and estimation performance. Additionally, the inherent spatial symmetry of phases in the tower structure is reflected in the parameter estimation results for internal faults involving these phases.