A Fault Data Based Method for Zero-Sequence Impedance Estimation of Mutually Coupled Transmission Lines

Line impedances estimation is of great importance in power system studies. Different software are used in utilities to calculate line impedances using the line conductor and structure data. The calculated values cannot be reliable due to inaccurate information or change in atmospheric condition. Also, since there is a lack of communication between different departments such as system protection, line construction, etc., a line conductor/structure may be changed while the affected departments are not notified. Most of the impedance estimation methods use phasor measurement units (PMUs) in the protection relays which are connected to protection class current transformers (CTs) that do not provide accurate currents compared to metering class CTs. These methods not only require PMUs in the substations, but also fail to measure zero-sequence voltages and currents due to inadequate zero-sequence components under normal operation. In parallel transmission lines, zero-sequence impedance estimation is even more challenging. This paper introduces a method for estimating the self and mutual zero-sequence impedances for mutually coupled transmission lines using recorded fault data. Extensive simulation and protective relay test results in RSCAD/RTDS indicate that the proposed approach has high accuracy in estimating the self and mutual zero-sequence impedances as well as the fault location in parallel transmission lines.