# Reliable directional relaying for T-Connected Series-Compensated transmission lines

## TL;DR

This paper introduces a new directional relaying algorithm for series-compensated transmission lines that reliably detects fault directions under various conditions.

## Contribution

The novel algorithm uses impedance locus in the positive-sequence circuit to determine fault direction with high accuracy across different scenarios.

## Key findings

- The algorithm performs well under varying prefault power factors and active power flow directions.
- It was tested successfully for multiple fault types, locations, and compensation ratios.
- The scheme was validated on a T-connected multi-terminal Egyptian transmission system.

## Abstract

This article introduces an extensive directional relaying algorithm designed for series-compensated transmission lines. The proposed algorithm relies on observing the locus of the calculated impedance of the change of the positive-sequence circuit. Both the voltage and current signals in positive sequence circuit are observed to acquire the impedance perceived by the relay. The fault direction is identified by the quadrant in which the locus of the obtained impedance settles. The proposed algorithm is distinguished by its high performance under varying prefault power factor and active power flow direction. It is tested for a range of fault types, varying fault resistance values, diverse fault locations, and different compensation ratios. All tests have been conducted while considering the nonlinear behaviour of the shunt metal oxide varistor (MOV) with the series-compensation capacitor. Furthermore, the proposed scheme is validated with a T-connected multi-terminal Egyptian transmission system. It is extensively tested and compared with other relevant schemes in the literature.

The online version contains supplementary material available at 10.1038/s41598-025-33564-9.