Ring Main Unit（RMU）
Designed for the most demanding secondary distribution networks, our Gas Insulated Ring Main Unit (GIS RMU) is a fully sealed, compact, and climate-independent switchgear. All primary live parts—including the busbars, load break switches, and circuit breakers—are completely enclosed in a robotically laser-welded stainless steel tank filled with SF6 gas (or eco-friendly gas alternatives) as the insulation and arc-quenching medium.
Strictly type-tested to IEC 62271-200, this GIS RMU guarantees zero exposure to environmental elements like high humidity, dust, salt spray, or flooding. It provides a fit-and-forget solution with a 30-year design life, making it the industry standard for modern urban grids, renewable energy plants, and heavy industrial applications.
Core Engineering Advantages
• Hermetically Sealed & Climate-Independent: The primary gas tank boasts an IP67 protection rating. It is completely immune to external environmental conditions, ensuring stable operation in coastal areas, deserts, or underground substations subject to high moisture.
• Compact Footprint: By utilizing gas insulation, the clearance between live phases is drastically reduced. This results in a switchgear footprint up to 50% smaller than traditional Air Insulated Switchgear (AIS), saving highly valuable real estate in city centers and wind turbine towers.
• Zero Routine Maintenance: The sealed gas tank requires zero maintenance on the high-voltage components over its entire lifespan. This translates to significantly lower Operational Expenditure (OPEX) and eliminates the need for frequent site visits.
• Maximum Operator Safety: Features a built-in mechanical interlocking system and a dedicated pressure relief valve. In the rare event of an internal fault, the arc gases are directed downwards or backwards into the cable trench, fully complying with IAC AFL / AFLR safety standards.
• Flexible Configurations (Compact or Extensible): Available in standard non-extensible blocks (e.g., CCV, CCC, CCF) for simple ring networks, or as fully extensible modules that can be joined via shielded solid insulated busbars for future grid expansion.
• Smart Grid Ready: Pre-engineered to house motorized mechanisms, protection relays (self-powered or auxiliary), and Remote Terminal Units (RTU) for SCADA monitoring, enabling rapid fault isolation and power restoration.
Technical Specifications
Applicable Standards | IEC 62271-200, IEC 62271-100, IEC 62271-103 |
Rated Voltage | 12kV / 17.5kV / 24kV |
Rated Frequency | 50Hz / 60Hz |
Insulation Medium | SF6 Gas / Eco-Gas Alternatives |
Rated Current (Busbar) | 630A / 1250A |
Rated Current (LBS / VCB) | 630A (LBS) / 630A or 1250A (VCB) |
Short-Circuit Breaking Capacity | 21kA / 25kA |
Short-Time Withstand Current | Up to 25kA for 3s |
Internal Arc Classification (IAC) | IAC A-FL / IAC A-FLR 21kA/1s |
Degree of Protection | Gas Tank: IP67 / Enclosure: IP3X to IP4X |
Gas Leakage Rate | < 0.1% per year |
Main Applications
• Renewable Energy Integration: Inside wind turbine towers and solar PV collector networks due to its compact size and high reliability.
• Urban Underground Networks: Basement substations and compact utility kiosks in densely populated cities.
• Harsh Environments: Coastal facilities, mining sites, and railway power distribution.
• Commercial Complexes: Hospitals, airports, and large shopping malls requiring uninterrupted power supply.
Q1. What is a GIS RMU and what are its primary applications?
A: A Gas Insulated Ring Main Unit (GIS RMU) is a compact, metal-enclosed switchgear that uses Sulfur Hexafluoride (SF6) gas as the insulating and arc-extinguishing medium. It is primarily used in secondary distribution networks, urban high-rise buildings, underground substations, and wind/solar farms to receive and distribute 12kV–36kV power.
Q2. What are the main advantages of GIS over Air Insulated Switchgear (AIS)?
A: The primary advantages of GIS are its ultra-compact footprint and its environmental resilience. Because all high-voltage live parts are sealed in a stainless steel gas tank, the unit is immune to moisture, dust, salt spray, and small animals, making it much more reliable than AIS in harsh environments.
Q3. How do you ensure the gas tightness of the SF6 tank?
A: At our Shanxi factory, the gas tanks are made of high-quality 304 stainless steel and are welded using robotic laser technology. Every tank undergoes a Helium Leak Test to ensure the annual leakage rate is less than 0.1%, guaranteeing a service life of over 30 years without gas refilling.
Q4. What monitoring features are included for gas safety?
A: Each GIS RMU is equipped with an SF6 Gas Density Monitor (Pressure Gauge) with temperature compensation. This gauge provides a clear visual status (green/red zones) and can be fitted with alarm contacts to alert your control room if the pressure drops below the safety threshold.
Q5. Is the GIS RMU "Maintenance-Free"?
A: Yes. The primary high-voltage circuit is hermetically sealed within the gas tank, which protects it from oxidation and contamination. This makes the GIS RMU virtually maintenance-free for its entire service life. You only need to perform periodic visual inspections and verify the mechanical operation of the external linkages.
Q6. What types of functional modules (units) do you offer?
A: Our GIS RMU features a modular design that can be configured as a single unit or an extensible string:
C-Unit: Load Break Switch module.
F-Unit: Switch-Fuse combination module.
V-Unit: Vacuum Circuit Breaker module.
D-Unit: Direct Cable Connection module.
Q7. How does the GIS RMU handle Internal Arc Faults?
A: Safety is our top priority. Our GIS units are designed with Internal Arc Classification (IAC). In the rare event of an internal fault, the gas tank is equipped with a pressure relief flap on the bottom or back to safely vent the gases away from the operator.
Q8. Can the GIS RMU be used in high-altitude or coastal areas?
A: Absolutely. Since the insulation is provided by the SF6 gas inside a sealed tank rather than external air, the dielectric strength is unaffected by altitude (up to 4000m) or high humidity. The outer cabinet is also treated with multi-layer anti-corrosive paint for coastal durability.
Q9. Does your GIS RMU support Smart Grid integration?
A: Yes. We can integrate an Electronic Feeder Terminal Unit (FTU) and motorized mechanisms. This allows for "Three-Remote" functions (Remote Signaling, Measuring, and Control) via Modbus or IEC 60870-5-104 protocols, making it compatible with any modern SCADA system.
Q10. What testing standards do your GIS units comply with?
A: All GIS RMUs are manufactured and tested in accordance with IEC 62271-200. We provide a complete technical package, including Type Test Reports (covering short-circuit, temperature rise, and internal arc) and a Factory Acceptance Test (FAT) report for every shipment.
