The Impact of the Transformer Inrush Current on the Zero Sequence Current Protection Settings Calculation for the Overhead Lines 110 Kv and Higher

Currently, the calculation of the parameters for the operation of current protections of the zero sequence of overhead power lines is carried out in accordance with the Methodological Guidelines for the calculation and selection of settings for backup current protections of 110 kV and higher power lines [1], developed by JSC SO UES in 2023. The approach described in them to calculating these parameters is based on the methodology set out in the guidelines for relay protection “Zero- sequence current protection against earth faults of the 110-500 kV line” [2], which were released in 1980. Since the release of this document, approaches to the implementation of relay protection complexes for electric power facilities have changed significantly. Changing the element base requires a revision of approaches to calculating the response parameters. In this article, a comparison of old and new approaches used to account for the inrush current surge is performed, and a new algorithm for calculating the zero sequence current protection settings is presented.