RTU

An RTU is a microprocessor-based device that monitors and controls field equipment on behalf of the SCADA system. In a substation, it sits at the boundary between the IED-level IEC 61850 world and the WAN-facing DNP3 or IEC 60870-5-104 world.

What it does

• Telemetry collection — polls IEDs, meters, and other field devices.
• Protocol translation — speaks IEC 61850 MMS southbound, DNP3 or 60870-5-104 northbound.
• Local processing — deadband filtering, alarm aggregation, data compression to reduce upstream bandwidth.
• Local autonomy — continues logging and executing pre-configured control logic during WAN outages, syncing back when connectivity returns.
• Control execution — receives operator commands from SCADA, applies them to the field devices.

The virtualised RTU

Traditional RTUs were physical appliances mounted in the substation cabinet. The current pattern in many GB and EU control rooms is a virtualised RTU (vRTU) — the same software function deployed as a VM in the control-centre data hall, co-located with the ADMS and EMS it feeds.

That deployment model centralises the operational footprint (one cluster to patch instead of hundreds of cabinets) but changes the failure mode: a substation-edge RTU has a blast radius of one substation; a virtualised RTU running in a shared cluster has a blast radius of every substation it serves.

RTU Data Concentrator

A common pattern between RTUs and SCADA is the RTU Data Concentrator — an aggregation layer that takes inputs from many RTUs, performs site-level processing, and forwards a consolidated stream to the SCADA front-end. Typically deployed in redundant main/hot-standby pairs.