Gas Insulated Ring Main Unit (RMU) 36kV offering compact solution for MV system

Ring Main Unit (RMU) 36kV

36kV Gas Insulated Ring Main Unit (RMU) is a compact, metal-enclosed medium-voltage switchgear designed for 36kV (40.5kV maximum system voltage) distribution networks. It integrates switching, protection, isolation, and control functions within a sealed gas-insulated enclosure. The primary live parts are housed in a stainless-steel tank filled with SF6 gas or environmentally friendly alternative insulating gas, providing excellent dielectric strength, arc-quenching capability, and long-term reliability.

36kV RMUs are widely used in utility substations, industrial power systems, renewable energy plants, transportation infrastructure, and urban distribution networks where high reliability, compact installation, and minimal maintenance are required.

Main Features
·Rated voltage: 36 kV
·Highest system voltage: 40.5 kV
·Fully sealed gas-insulated construction
·Compact and modular design
·Maintenance-free sealed gas tank
·High operational safety with interlocking mechanisms
·Excellent insulation against dust, humidity, and pollution
·Expandable feeder configurations
·Remote monitoring and SCADA compatibility
·Optional internal arc classification

Typical Functional Modules
A 36kV RMU may include:
·Load Break Switch (LBS)
·Vacuum Circuit Breaker (VCB)
·Fuse Switch Combination
·Busbar Module
·Cable Switch Module
·Bus Section Switch
·Metering Module
·Earthing Switch
·Voltage Transformer (VT)
·Current Transformer (CT)
·Remote Terminal Unit (RTU)

Typical configurations:
CCC – Three load break switches
CCF – Two cable switches + one fused transformer feeder
CCV – Two cable switches + one vacuum circuit breaker
Modular expandable arrangements for additional feeders

Typical Technical Specifications
·Rated Voltage: 36 kV
·Highest System Voltage: 40.5 kV
·Rated Frequency: 50/60 Hz
·Rated Current: 630 A (1250 A optional)
·Rated 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): 170 kV
·Power Frequency Withstand Voltage: 70/95 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
·Service Life: ≥30 years
·Applicable Standards: IEC 62271-1, IEC 62271-200, IEC 62271-103

Main Components
·Stainless-steel hermetically sealed gas tank
·SF6 gas or eco-insulating gas
·Three-position load break switch (ON–OFF–EARTH)
·Vacuum interrupter (VCB module)
·Copper busbars
·Cable connection compartment
·Earthing switch
·Mechanical and electrical interlocking system
·Gas density indicator
·Pressure relief device
·Low-voltage control cabinet

Working Principle
·The incoming cable energizes the RMU through a load break switch.
·Power flows through the insulated busbar to outgoing feeders.
·Under normal conditions, load break switches perform switching operations.
·During a fault, the fuse or vacuum circuit breaker interrupts the fault current.
·The faulty feeder is isolated while the remaining feeders continue supplying power, maintaining network continuity.

Advantages
·Compact installation footprint
·High insulation reliability
·Maintenance-free sealed tank
·Excellent resistance to harsh environmental conditions
·High operational safety
·Reduced outage duration through rapid fault isolation
·Long service life
·Suitable for smart-grid automation
·High equipment availability

Typical Applications
·Utility secondary substations
·Urban underground distribution networks
·Industrial plants
·Commercial buildings
·Wind power plants
·Solar photovoltaic farms
·Data centers
·Airports
·Hospitals
·Railway and metro power systems
·Mining operations
·Oil and gas facilities

Applicable 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
·IEC 60529 – Degrees of protection (IP Code)

Typical Ratings Summary
·Rated Voltage: 36 kV
·Highest System Voltage: 40.5 kV
·Rated Current: 630 A
·Short-Circuit Current: 20–25 kA
·BIL: 170 kV
·Power Frequency Withstand: 70/95 kV
·Insulation Medium: SF6 or eco-gas
·Protection Degree: IP67 (sealed gas tank)
·Installation: Indoor / Outdoor
·Automation: Optional SCADA / RTU
·Service Life: ≥30 years

Key Benefits
A 36kV Gas Insulated Ring Main Unit (RMU) offers a highly reliable and compact solution for medium-voltage distribution systems. Its sealed gas-insulated design minimizes maintenance, enhances operational safety, and ensures dependable performance in harsh environments. With modular configurations, remote monitoring capabilities, and compliance with IEC standards, it is well suited for modern utility, industrial, and renewable energy applications where continuous power supply and efficient fault isolation are essential.