12kV / 24kV SF6 Insulated Ring Main Unit | Compact RMU

Overview

This ring main unit is a factory-assembled, metal-enclosed medium voltage switchgear designed for reliable power distribution in secondary networks. All live parts are housed inside a stainless-steel tank filled with SF6 gas, which provides complete insulation and protects them from dust, humidity and salt spray.

The modular design allows functional units to be combined — switch-fuse, circuit breaker, load break, PT and metering — so the assembly matches the network topology exactly. With a compact footprint and an IP67 rated tank, the unit suits indoor substations, outdoor kiosks and underground vaults.

Each RMU is shipped complete with all internal wiring and the gas filling already in place. Installation requires only anchoring the enclosure, connecting the power cables and wiring the auxiliary signals.

Key Features

• Sealed SF6 insulated tank — SF6 gas insulation maintains stable dielectric performance regardless of ambient conditions, and the sealed-for-life tank removes the need for gas refilling or regular servicing.
• Modular configuration — up to six modules can be combined, including C, F, V, PT and metering units, to suit complex ring-main or radial networks.
• Compact footprint — the design saves up to 50% of the space required by traditional air-insulated switchgear.
• Safety interlocks and pressure relief — integrated interlocks prevent mal-operation, and pressure relief devices protect against internal arc faults.
• Weatherproof tank construction — the stainless-steel tank uses anti-corrosion treatment and carries an IP67 rating, so it is suitable for harsh environments.
• Wide current range — up to 630 A for load-break and 200 A for fuse-combination units, or up to 1250 A with a circuit breaker.
• Pre-wired and pre-tested — the unit leaves the factory fully wired and tested, with plug-in connections for the field cables.

Technical Specifications

Module Configurations

• C module — load-break switch with earthing switch.
• F module — switch-fuse combination, being a load switch with fuse.
• V module — vacuum circuit breaker with earthing switch.
• PT module — voltage transformer with load switch.
• M module — metering unit with current and voltage transformers.
• CB module — circuit breaker with protection relay.
• Compatibility — all modules are fully compatible and can be combined in any sequence.

Applications

• Urban secondary distribution networks — ring-main and radial feeders.
• Commercial complexes and high-rise buildings — distribution for shopping malls and multi-storey developments.
• Industrial plants — including mining sites and oil and gas facilities.
• Transport infrastructure — airports, railway stations and metro power supply.
• Renewable generation — wind farms and solar photovoltaic substations.
• Prefabricated substations — pad-mounted and kiosk type compact substations.

Installation Conditions

• Each RMU is shipped complete with all internal wiring and the gas filling already in place.
• Installation requires only anchoring the enclosure, connecting the power cables and wiring the auxiliary signals.
• Detailed instruction manuals and wiring diagrams are supplied with the unit.
• The IP67 tank allows installation indoors, in outdoor kiosks or in underground vaults; the cable compartments are rated IP4X.
• Operating ambient temperature range is -25 °C to +55 °C with relative humidity up to 95% non-condensing.

How to Select

• Rated voltage — 12 kV, 24 kV or 36 kV.
• Rated current — for example 630 A or 1250 A.
• Number of modules and their types — for example C + F + V.
• Cable entry direction — top, bottom or side.
• Auxiliary voltage — AC or DC, 110 V or 220 V.
• Special accessories — current transformers, voltage transformers, surge arresters or a remote control panel.
• Example order code — RMU-24-630-C-F-V-PT, being 24 kV, 630 A busbar, load-break plus fuse-combination plus circuit-breaker plus PT module.

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