A Ring Main Unit (RMU) is a high-voltage switchgear used in ring distribution networks, mainly for urban residential areas, high-rise buildings, factories and prefabricated substations. It connects each outgoing cabinet through a ring busbar, ensuring reliable and flexible power supply, with each outgoing cabinet being a RMU.
A ring main unit typically consists of the following main parts:
Cabinet: made of steel plates bent and welded or of a fully enclosed metal structure, including the top cover, bottom plate, front and rear panels, side panels and pillars, with a protection level generally of IP2X.
Busbar compartment: located at the top of the cabinet for arranging the main busbars, which are covered with insulating sleeves; a busbar channel or instrument box can be added on the top of the cabinet.
Load switch compartment: the middle area, where insulating partitions are installed between the load switch and other components, with a simple arc extinguishing device, allowing three operating positions: connect, disconnect, and ground.
Instrument compartment: usually at the front of the busbar compartment, separated by steel plates, for installing current, voltage and protection instruments.
Earthing switch and fuse: the load switch cabinet usually comes with an earthing switch, and the combination of load switch and fuse can achieve automatic tripping and overcurrent protection.
Busbar compartment: located at the top of the cabinet for arranging the main busbars, which are covered with insulating sleeves; a busbar channel or instrument box can be added on the top of the cabinet.
Load switch compartment: the middle area, where insulating partitions are installed between the load switch and other components, with a simple arc extinguishing device, allowing three operating positions: connect, disconnect, and ground.
Instrument compartment: usually at the front of the busbar compartment, separated by steel plates, for installing current, voltage and protection instruments.
Earthing switch and fuse: the load switch cabinet usually comes with an earthing switch, and the combination of load switch and fuse can achieve automatic tripping and overcurrent protection.
Ring main units can be classified according to different standards:
Gas compartment structure: integrated type and modular type.
Overall structure: American style and European style. The American style is mostly designed for outdoor use, with a small volume, maintenance-free, and a compact structure; the European style adopts an independent compartment design, with busbars and load switches sealed in SF6 gas, allowing flexible combination and easy expansion.
Insulation material: solid insulation, air insulation, SF6 gas insulation. SF6 gas insulated cabinets possess excellent insulation and arc extinguishing performance, suitable for promotion in medium-voltage distribution networks.
Installation environment: indoor ring main units and outdoor ring main units.
Gas compartment structure: integrated type and modular type.
Overall structure: American style and European style. The American style is mostly designed for outdoor use, with a small volume, maintenance-free, and a compact structure; the European style adopts an independent compartment design, with busbars and load switches sealed in SF6 gas, allowing flexible combination and easy expansion.
Insulation material: solid insulation, air insulation, SF6 gas insulation. SF6 gas insulated cabinets possess excellent insulation and arc extinguishing performance, suitable for promotion in medium-voltage distribution networks.
Installation environment: indoor ring main units and outdoor ring main units.
Core Components
Load Switch: Capable of breaking light load currents under load, typically equipped with a fuse, featuring strong arc-extinguishing capability, suitable for line and transformer switching operations.
Isolating Switch: Used to ensure clear separation between live and dead parts following the opening of the circuit breaker, facilitating operation and safety maintenance.
Busbar System: The ring busbar connects each outgoing cabinet, employing a staggered contact plug-in design to ensure reliable current transmission.
Functional Features
The EXELEK ring main unit has a compact structure and flexible operation, enabling power distribution, system protection, fault isolation, and automated control. Its modular design facilitates expansion and maintenance while improving power supply reliability and safety.
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