Methodology for Selecting Line Protection Schemes in Substations in EPM

This document presents a method developed by EPM to select transmission line protection schemes in a technical, standardized, and cost-efficient way. The approach combines classification criteria (SIR, line length, topology, and connection type) with a performance validation process based on large-scale short-circuit simulations under critical operating scenarios. Three protection schemes are evaluated: 87L, with high sensitivity but security risks; 85-21L/67N, a more economical and stable alternative; and 21L+67/67N, applicable to radial load-fed lines. For lines with SIR < 20 and length > 10 km operating in a ring configuration, compliance with performance criteria is verified through simulation to assign either the 8521L/67N scheme or, if requirements are not met, the 87L scheme.…