Gas Insulated Ring Main Unit (RMU) 24kV provides reliable switching, protection, sectionalizing, and fault isolation

Ring Main Unit (RMU) 24kV

24kV Gas Insulated Ring Main Unit (RMU) is a factory-assembled, metal-enclosed medium-voltage switchgear designed for 24kV distribution networks. It provides reliable switching, protection, sectionalizing, and fault isolation while maintaining uninterrupted power supply to healthy sections of the network. The primary live components are enclosed in a sealed stainless-steel tank filled with SF6 gas or environmentally friendly insulating gas, providing excellent insulation and arc-quenching performance.

Main Features
·Rated voltage: 24 kV
·Compact, fully sealed gas-insulated construction
·Maintenance-free sealed-for-life gas tank
·High operational reliability and safety
·Suitable for indoor and outdoor substations
·Modular and expandable design
·Low maintenance requirements
·Internal arc classification available
·Compatible with SCADA and distribution automation systems

Typical Functional Modules
A 24kV RMU can be configured with combinations of:
·Load Break Switch (LBS)
·Vacuum Circuit Breaker (VCB)
·Fuse Switch Combination
·Busbar Module
·Cable Switch Module
·Metering Module
·Earthing Switch
·Bus Section Switch
·Remote Terminal Unit (RTU)

Typical arrangements include:
CCC – Three load break switches
CCF – Two cable switches + one fuse switch
CCV – Two cable switches + one vacuum circuit breaker
Expandable modular configurations for additional feeders

Typical Technical Specifications
·Rated Voltage: 24 kV
·Highest System Voltage: 24/25.8 kV
·Rated Frequency: 50/60 Hz
·Rated Current: 630 A (1250 A optional)
·Short-Time Withstand Current: 20–25 kA, 3 s
·Peak Withstand Current: 50–63 kA
·Rated Short-Circuit Breaking Current: Up to 25 kA
·Lightning Impulse Withstand Voltage (BIL): 125 kV
·Power Frequency Withstand Voltage: 50 kV (1 min)
·Protection Degree: IP4X enclosure, IP67 sealed gas tank
·Mechanical Endurance: ≥2,000–10,000 operations
·Gas Leakage Rate: Typically <0.1–0.2% per year
·Applicable Standards: IEC 62271-1, IEC 62271-200, IEC 62271-103

Main Components
·Stainless-steel sealed gas tank
·SF6 gas or eco-insulation gas
·Load Break Switch (LBS)
·Vacuum Interrupter (VCB modules)
·Three-position switch (ON–OFF–EARTH)
·Copper busbars
·Cable termination compartment
·Low-voltage control cabinet
·Mechanical and electrical interlocking system
·Gas pressure indicator
·Pressure relief device

Working Principle
·Incoming feeder energizes the RMU through a cable switch.
·The internal insulated busbar distributes power to outgoing feeders.
·During normal operation, load break switches perform switching operations.
·In case of a fault, the fuse or vacuum circuit breaker interrupts the fault current.
·The faulty feeder is isolated while the remaining network continues operating, ensuring high service continuity.

Advantages
·Compact footprint
·Excellent insulation performance
·High reliability in polluted, humid, and coastal environments
·Minimal maintenance
·Long service life (typically 30 years or more)
·High personnel safety
·Reduced outage duration through rapid fault isolation
·Suitable for smart-grid automation and remote operation

Typical Applications
·Urban distribution substations
·Industrial facilities
·Commercial complexes
·Residential distribution networks
·Renewable energy plants
·Wind farms
·Solar photovoltaic plants
·Airports
·Hospitals
·Railway and metro power systems
·Data centers
·Utility secondary substations

Applicable International Standards
·IEC 62271-1 – High-voltage switchgear and controlgear – Common specifications
·IEC 62271-200 – AC metal-enclosed switchgear and controlgear
·IEC 62271-103 – Switches for rated voltages above 1 kV
·IEC 61869 – Instrument transformers (when applicable)
·IEC 60529 – Degrees of protection (IP Code)

Typical Ratings Summary
·Rated Voltage: 24 kV
·Rated Current: 630 A
·Fault Current: 20–25 kA
·BIL: 125 kV
·Power Frequency Withstand: 50 kV
·Insulation Medium: SF6 or eco-gas
·Installation: Indoor / Outdoor
·Protection Degree: IP67 (sealed tank)
·Automation: Optional SCADA / RTU
·Service Life: ≥30 years

A 24kV Gas Insulated RMU is widely used in modern medium-voltage distribution systems due to its compact size, sealed construction, high reliability, and ability to maintain network continuity through efficient fault isolation. It is particularly well suited for urban infrastructure, industrial plants, renewable energy installations, and smart distribution networks.