Zero-Sequence Impedance Estimation in Mutually Coupled Transmission Lines Using Fault Record Data

Estimation of line impedances is of great interest to power system engineers. Power utility companies use different software to calculate line impedances based on the conductor and structure types. However, the calculated values cannot remain accurate due to atmospheric condition. Also, due to lack of communication between the line construction, maintenance, and other departments, a line conductor/structure may be partially/totally changed without notifying the affected departments. Various estimation methods are used to dynamically obtain line impedance values. The majority of these methods use phasor measurement units (PMU s) for the impedances estimation. These methods require PMU s in the substations and fail to measure zero-sequence voltages/currents due to inadequate zero-sequence components under normal operation. The estimation of zero-sequence impedances is even more challenging for parallel transmission lines which are mutually coupled. This study proposes a method for estimating the self and mutual zero-sequence impedances for mutually coupled transmission lines using recorded fault data by protective relays. Extensive simulation 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.