{
  "language": "en",
  "interfaceLanguage": "en",
  "url": "https://voltformer.com/articles/ring-main-units-rmu-for-compact-distribution-and-smart-grid-automation",
  "id": "art-22",
  "slug": "ring-main-units-rmu-for-compact-distribution-and-smart-grid-automation",
  "title": "Ring Main Units (RMU) for Secondary Distribution: Architecture, CCF Topologies, and Telemetry Automation",
  "summary": "Gas-insulated compact RMU switchgear (24 kV / 36 kV), CCF and CCCF topologies, motorized load-break switches, Fault Passage Indicators (FPI), and IEC 60870-5-104 telemetry integration.",
  "readTime": "8 min read",
  "date": "2026-08-18",
  "author": "Voltformer Smart Grid & Secondary Distribution Desk",
  "category": "RMU & Smart Distribution",
  "tags": [
    "Ring Main Unit",
    "RMU",
    "CCF Topology",
    "Smart Grid",
    "IEC 60870-5-104"
  ],
  "contentMarkdown": "### 1. Secondary Distribution Ring Main Unit (RMU) Functions\n\nRing Main Units provide compact medium-voltage protection and switching in underground distribution loops (ring networks) for compact transformer kiosks and commercial facilities.\n\n### 2. Standard Functional Module Configurations\n\n| RMU Configuration Code | Composition of Functional Blocks | Typical Application |\n|---|---|---|\n| **CCF** | 2 Cable Switches (C) + 1 Fuse-Switch (F) | Compact kiosks up to $1250\\text{ kVA}$ |\n| **CCV** | 2 Cable Switches (C) + 1 Vacuum Circuit Breaker (V) | Substation transformers $> 1250\\text{ kVA}$ |\n| **CCCF / CCCV** | 3 Cable Ring Switches + 1 Transformer Feeder | Ring branch nodes and meshed grids |\n| **CCCC** | 4 Cable Load-Break Switches | Sectionalizing and bus-tie loop stations |\n\n### 3. Smart Grid Automation & Telecontrol Protocols\n\nTo enable automated Fault Location, Isolation, and Service Restoration (FLISR):\n- **Directional Fault Passage Indicators (FPI):** Detect phase-to-phase and earth fault current paths.\n- **24 VDC Motorized Mechanisms:** Actuate switches in $< 3\\text{ seconds}$ via SCADA commands.\n- **Protocol Support:** **IEC 60870-5-104** (Ethernet TCP/IP) and **DNP3 Secure**.\n\n### 4. Hermetic Sealed Tank Reliability\n\nPrimary 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**.\n\n*Reference: IEC 62271-200:2021; IEC 60870-5-104; IEEE Std C37.20.3.*",
  "contentLanguage": "en",
  "sources": []
}