A merging unit (MU) is a key building block of modern digital substations. It converts the analog signals from current transformers (CTs) and voltage transformers (VTs) into time-synchronized digital measurements and publishes them as IEC 61850 Sampled Values (SV) over an Ethernet-based process bus. By moving the analog-to-digital conversion close to the primary equipment, merging units reduce copper wiring, improve flexibility, and enable multiple protection, control, and monitoring devices to access the same measurement data stream.
Merging units are essential for digital substation architectures and virtualized protection systems (vPAC), where protection functions run as software rather than dedicated hardware relays. They provide the accurate, time-synchronized measurement data required for protection, automation, fault recording, and power quality applications while supporting modern networking technologies such as PRP, HSR, and Precision Time Protocol (PTP). As utilities continue their transition from copper-based designs to software-driven protection systems, merging units serve as the critical interface between the physical power system and the digital protection environment.
