615 Series Protection Relay Firmware Update 5.1.20 Release Notes

This document details firmware update release 5.1.20 for ABB's 615 series protection relays (REF615, REM615, RET615, etc.), including critical cyber security fixes for CVE-2021-22283 and improvements to self-supervision, protection functions, and communication. It also references the previous release 5.1.19, which addressed Ripple20 vulnerabilities, time counter rollover issues, and GOOSE/IEEE 1588 communication enhancements.