Air Insulated Ring Main Unit

Air Insulated Ring Main Unit (RMU) is a modular, medium-voltage switchgear system rated up to 24 kV, engineered for secondary power distribution networks. Utilizing atmospheric air as the primary dielectric medium, this configuration houses load break switches, earthing switches, and vacuum circuit breakers within a compact, compartmentalized sheet-steel enclosure. It provides reliable circuit switching, overload protection, and fault isolation for radial and loop distribution systems without relying on pressurized SF6 gas. 

SF6-Free Dielectric Design: Utilizes solid insulation and dry atmospheric air, eliminating greenhouse gas tracking, pressure monitoring sensors, and regulatory compliance risks over the operational lifecycle.

Triple-Compartment Separation: The enclosure isolates the busbar, cable connection, and switching mechanisms into independent metal compartments, preventing localized faults from propagating.

Mechanical Interlocking: Integrated foolproof interlocking cams prevent improper operational sequences, such as opening the load break switch while the earthing switch is closed.

Compact Footprint: Engineered with a reduced depth and width profile, fitting into prefabricated kiosk substations, underground vaults, and narrow industrial switchrooms.

Visible Isolation Break: Transparent viewing windows allow direct physical inspection of the switch blade position before maintenance work begins.

Urban Distribution Networks: Secondary substation nodes in municipal power grids routing underground cable rings.

Solar & Wind Balance of Plant: Medium-voltage collection rings connecting step-up transformer stations in renewable energy sites.

Industrial Facilities: Factory substations requiring localized power distribution and motor/transformer protection.

Commercial Real Estate: Basement distribution rooms in large commercial complexes, data centers, and institutional campuses.

Feeder Configuration: Combinations of load break switch (LBS) modules, vacuum circuit breaker (VCB) modules, and direct busbar extensions built to single-line diagram (SLD) requirements.

Control & Metering Integration: Provisions for integrated protection relays (self-powered or auxiliary-powered), multi-tariff energy meters, and remote terminal units (RTUs) for SCADA telemetry.

Enclosure Finishes: Cold-rolled steel plates treated with zinc-phosphate anti-corrosion priming and electrostatic epoxy powder coating (RAL 7035 standard or custom color codes). High-salinity coastal environment protection packages available.

Cable Entry Options: Bottom cable entry with split gland plates or customized base frames matched to specific civil trench layouts.

Engineering Downloads: Need layout verification for your project? Access downloadable 2D/3D CAD blocks, BIM models, and comprehensive PDF technical catalogues by submitting your project single-line diagram (SLD) through our technical inquiry portal.

Production runs on CNC laser cutting and turret punch machinery to maintain enclosure dimensional tolerances within +/- 0.1 mm. Robotic gas-metal arc welding ensures structural seam integrity across all modular frames.

Every assembled unit undergoes factory acceptance testing (FAT) before dispatch:

Dielectric Testing: Power frequency withstand voltage testing and lightning impulse voltage testing.

Partial Discharge Measurement: Conducted to verify insulation system integrity under high electrical stress.

Mechanical Operation Trials: 500 repetitive mechanical close-open cycles executed on switches and circuit breakers to verify spring mechanism endurance.

Circuit Resistance Verification: Micro-ohm meter testing performed on primary current paths to confirm low contact resistance.

Type Test Reports: Issued by independent ILAC-accredited laboratories verifying compliance with IEC 62271-200.

Quality Management: ISO 9001:2015 certified manufacturing facility.

Supplied Technical Documentation: Each shipment includes certified general arrangement (GA) drawings, electrical schematic diagrams, bilingual operation manuals, factory test sheets, and spare parts lists.

Export Packaging: Units are sealed in moisture-barrier vacuum foil with silica gel desiccant packs, secured inside heat-treated export-grade plywood crates (ISPM 15 compliant).

Lifting & Handling: Crates feature dedicated forklift slots and overhead crane lifting lugs to prevent mechanical stress on switchgear frames during transit.

Lead Time: Standard configurations ship within 4 to 6 weeks; engineered-to-order projects require 8 to 10 weeks subject to SLD complexity.