REX640 Protection Relay Firmware Update 1.2.3 Release Notes

This document details firmware update release 1.2.3 for the ABB REX640 protection relay, applicable to units with Product Connectivity Level 3 (PCL3) and firmware versions 1.2, 1.2.1, or 1.2.2 delivered before October 28, 2022. It outlines improvements in protection, engineering, and communication, including enhancements to compensated neutral unbalance voltage protection, SMV SCL configuration handling, and frequency measurement stability.