Overview

In modern medium-voltage (MV) distribution networks, Ring Main Unit (RMU) configurations are a foundational topology for achieving high reliability, continuous power delivery, and operational flexibility. An RMU is a compact, enclosed switchgear assembly used in ring-type distribution networks, where multiple RMUs interconnect to form looped paths for power distribution. This architectural approach ensures power can be delivered from either direction — maintaining supply even if one feeder segment is lost due to a fault or maintenance activity.

While RMUs provide a robust physical switching infrastructure, realising the full benefits of a smart, automated distribution network requires advanced telemetry, control, and fault management intelligence. This is where Elseta’s eRTU plays a critical role.

Challenges in RMU-Based Networks

Utilities deploying RMUs in looped feeder configurations face several challenges without automated remote control and monitoring:

Fault detection and isolation delays. Manual identification and switching prolong outage durations.

Limited visibility. Without remote measurement, network operators lack real-time data on power quality, load states, or fault progression.

Inefficient restoration. Loop automation demands fast, coordinated reconfiguration logic to restore service from alternate paths.

Operator safety. In the absence of secure remote control, field personnel risk exposure during physical operations.

Bidirectional flows. As utilities integrate distributed energy resources (DERs) and bidirectional power flows, the complexity of maintaining stable voltage, optimising load distribution, and coordinating protection increases significantly.

Elseta eRTU: Integrating Intelligence into RMUs

The eRTU from Elseta is an advanced remote terminal unit designed for RMUs, secondary substations, feeders, and other grid-edge devices. It combines measurement, control, automation logic, and communications into a modular edge-ready platform that seamlessly integrates with both traditional SCADA and modern smart grid systems.

Functionalities Enabled in RMU Configurations

Remote Monitoring and Control

eRTU enables secure remote operation of all switching devices within an RMU, including load break switches, breakers, and protective elements. Operators can read the real-time status of all connected RMU assets, execute remote switching commands from SCADA or control centres, and monitor the health and performance of transformer feeds and busbars. This significantly reduces manual field intervention, accelerates response times to network conditions, and enhances situational awareness for dispatchers and engineers.

Advanced Fault Management & Self-Healing

eRTU delivers comprehensive fault management by autonomously identifying transient versus permanent faults, isolating faulted segments, and triggering predefined automation logic to reconfigure the network. Its self-healing capability supports faster restoration of service through alternate paths, reduces outage duration, improves network reliability, and decreases dependency on manual fault location and switching. This is particularly valuable in looped RMU configurations where dynamic adaptation to network events is essential for continuity of service.

Power Quality & Load Data Analytics

eRTU’s high-precision measurement engine captures voltages, currents, and power metrics with detailed quality indicators, disturbance recordings, and event logs. It also collects load profiles that support optimal asset management. These rich datasets allow utilities to detect load imbalances, optimise energy flows, identify inefficiencies, and implement predictive maintenance strategies — capabilities that are critical for modern grids facing fluctuating load patterns and high penetration of distributed energy resources (DERs).

Flexible Communications & Security

Supporting multiple protocols (IEC 60870-5, DNP3, IEC 61850, Modbus, MQTT, REST API) and redundant communication paths (fiber, cellular, VPN), eRTU integrates easily into existing automation stacks. A layered cybersecurity architecture, including encrypted communications, role-based access control, integrated firewall, and IEC 62351 compliance, safeguards remote access even in exposed RMU locations.

Advantages for Utilities and Network Operators

By deploying eRTU with RMU infrastructure, utilities gain:

Improved Reliability & Continuity. Loop network configurations with intelligent control prevent single-point outages and ensure alternate supply paths are engaged swiftly when faults occur.
Faster Fault Response and Reduced Outages. Automated detection, isolation, and reconfiguration dramatically decrease mean time to repair (MTTR) and improve overall service availability.
Enhanced Operational Efficiency. Remote operations eliminate the need for frequent field dispatches, reducing operational costs and improving resource allocation. Detailed analytics support proactive maintenance and asset optimisation.
Scalability for Smart Grid Transition. With configurable logic and protocol versatility, eRTU enables utilities to expand from basic monitoring to full automation, including advanced DER integration and future-proof grid services.

Conclusion

In RMU-centric distribution topologies — whether urban loop networks or feeder automation schemes — the combination of robust switchgear and intelligent remote control units is essential. Elseta’s eRTU enriches the RMU with real-time measurement, secure remote control, self-healing automation, and rich analytics, transforming traditional distribution networks into resilient, responsive, and future-ready smart grid infrastructures.

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