Ring Main Units (RMU) for Secondary Distribution: Architecture, CCF Topologies, and Telemetry Automation
Gas-insulated compact RMU switchgear (24 kV / 36 kV), CCF and CCCF topologies, motorized load-break switches, Fault Passage Indicators (FPI), and IEC 60870-5-10
1. Secondary Distribution Ring Main Unit (RMU) Functions
Ring Main Units provide compact medium-voltage protection and switching in underground distribution loops (ring networks) for compact transformer kiosks and commercial facilities.
2. Standard Functional Module Configurations
| RMU Configuration Code | Composition of Functional Blocks | Typical Application |
|---|---|---|
| CCF | 2 Cable Switches (C) + 1 Fuse-Switch (F) | Compact kiosks up to 1250 kVA |
| CCV | 2 Cable Switches (C) + 1 Vacuum Circuit Breaker (V) | Substation transformers > 1250 kVA |
| CCCF / CCCV | 3 Cable Ring Switches + 1 Transformer Feeder | Ring branch nodes and meshed grids |
| CCCC | 4 Cable Load-Break Switches | Sectionalizing and bus-tie loop stations |
3. Smart Grid Automation & Telecontrol Protocols
To enable automated Fault Location, Isolation, and Service Restoration (FLISR):
- Directional Fault Passage Indicators (FPI): Detect phase-to-phase and earth fault current paths.
- 24 VDC Motorized Mechanisms: Actuate switches in < 3 seconds via SCADA commands.
- Protocol Support: IEC 60870-5-104 (Ethernet TCP/IP) and DNP3 Secure.
4. Hermetic Sealed Tank Reliability
Primary live busbars, switches, and disconnectors are enclosed inside a laser-welded stainless steel tank with IP65 ingress protection and >30-year gas tightness per IEC 62271-200.
*Reference: IEC 62271-200:2021; IEC 60870-5-104; IEEE Std C37.20.3.*