Evaluating Incremental-Quantity Protection Elements in Hybrid Transmission Lines with Overhead and Underground Segments

This paper evaluates the performance of incremental-quantity protection elements TD32 and TD21 in hybrid transmission lines (HTLs) that combine overhead transmission lines (OHLs) and underground cables (UGCs). Ground faults were simulated using a 380 kV/60 Hz power system in PSCAD, with six configurations and 216 fault scenarios per configuration under varying conditions, including fault time, location, resistance, and phase. Analysis through scatter and boxplot plots revealed significant differences in the operation times of protection functions between HTLs and OHLs, impacting overall system reliability. Specifically, the presence of UGCs alters fault detection times (Start Logic) and the performance of protective relays regarding incremental quantities, potentially leading to delays in fault clearance. These findings underscore the necessity for protective schemes to accommodate the unique dynamics of HTLs, enhancing overall system reliability and operational efficiency.