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Ring Main Unit

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Product Judgment & Technical Architecture

 

A Ring Main Unit (RMU) is a factory-assembled, metal-enclosed medium-voltage switchgear system deployed in ring-feed distribution networks. It integrates load break switches, vacuum circuit breakers, and fuse-switch combinations within a hermetically sealed enclosure to control, switch, and protect power transformers and cable lines.


Configurations: Modular and compact expandable setups ranging from 2-way to 5-way configurations (e.g., CCV, CBC, or customized layouts).


Insulation Technologies: SF6 gas-insulated systems (hermetically sealed for life with an annual leakage rate <0.05%) and eco-friendly solid dielectric / dry-air insulated alternatives.


Busbar Ratings: 630A continuous current for main busbars; 200A or 630A for feeder branches.

 
 

Product Selection Guide

 

Specify the RMU configuration matching grid voltage, short-circuit levels, and environmental conditions. 

 

Parameter Requirement

Standard Utility Application

Heavy-Duty / Industrial Application

Rated Voltage

12kV / 24kV

36kV

Rated Short-Circuit Current

20kA (3s)

25kA (3s)

Enclosure Protection

IP67 (Cable compartment / SF6 tank)

IP67 (Submersible tank option available)

Switching Mechanism

Spring-assisted manual / Motorized actuator

Motorized actuator with remote RTU integration

Operating Temperature

-25°C to +40°C

-40°C to +55°C (arctic/desert options)

 

Application Suitability
 

Utility Distribution Networks

Secondary substation nodes for urban ring networks, minimizing outage duration via sectionalizing switches.

Renewable Energy Integration

Medium-voltage collection grids in utility-scale solar photovoltaic farms and wind turbine pooling substations.

Industrial Facilities

Primary ring supply for manufacturing complexes, data centers, and water treatment pumping stations requiring dual-source power redundancy.

Infrastructure Projects

Underground utility tunnels, airports, and railway traction power supply lines.

 

SF6 Ring Main Unit

 

Manufacturing & Quality Control Capability

Manufacturing operations integrate automated laser cutting, robotic TIG welding, and helium leak detection to maintain structural and sealing integrity.


Sheet Metal Precision: Trumpf CNC fiber laser cutting and Amada multi-axis bending maintain enclosure dimensional tolerances within ±0.1mm.


Tank Sealing & Testing: Stainless steel (304) SF6 tanks undergo automatic robotic welding followed by 100% helium mass spectrometer leak detection testing to guarantee a 30-year operational lifespan.


Assembly Standards: Cleanroom assembly environments prevent particulate contamination in high-voltage compartments.


Factory Acceptance Testing (FAT): Every unit undergoes mechanical operation endurance testing (2,000 operations), power frequency withstand voltage testing (28kV to 70kV for 1min), micro-ohm contact resistance measurement, and partial discharge measurement (< 10pC at 1.2 U0).


Compliance Certifications: Tested and certified to IEC 62271-200, IEC 62271-102, and IEC 62271-100 standards by independent laboratories (KEMA/CESI compliant testing protocols).

 

Procurement Decision Parameters

Documentation Package Provided

Complete Type Test Reports (TTR), seismic qualification certificates, internal arc classification reports (IAC AFLR 20kA 1s), and detailed AutoCAD/EPLAN drawings for submittal approval.

 

Lead Time & Logistics

Standard production cycle is 4 to 6 weeks. Units are shipped in nitrogen-pressurized or sealed wooden crates configured for standard container loading or crane lifting.

 

Customization Capacity

Support for customized auxiliary switch contacts, integrated protection relays (Schneider, ABB, or SEL-compatible), motorized remote-terminal units (RTU), and specialized color coatings (RAL 7035 standard).

 

 

FAQ

 

Q: What is the operational lifespan of the SF6 gas tank in your RMU?

A: The stainless steel SF6 tank is a hermetically sealed system designed for a minimum service life of 30 years. Annual gas leakage is guaranteed below 0.1%, eliminating the need for on-site gas refilling during normal operations.

Q: Can your RMUs be retrofitted with motor operators for remote control SCADA integration?

A: Yes. Manual units feature modular mechanical interfaces that allow field installation of 24VDC or 48VDC motor operators, shunt trips, and auxiliary position switches without draining gas or dismantling the main busbar.

Q: What internal arc classification (IAC) ratings do your enclosures meet?

A: Standard enclosures are tested to IAC AFLR 20kA for 1 second, protecting operating personnel from internal overpressure and arc faults across front, lateral, and rear directions.

Q: What documents are included in the pre-shipment technical submittal?

A: Each shipment includes factory test reports (serial-number specific), certified general arrangement drawings, schematic wiring diagrams, operation and maintenance manuals, and independent laboratory type test certificates.

Q: Are your RMU switches capable of breaking full load currents repeatedly?

A: The load break switches are rated for class E3 mechanical and electrical endurance, capable of performing a minimum of 100 full-load breaking operations at rated current without contact maintenance.

Q: What is your standard factory acceptance testing (FAT) protocol?

A: FAT procedures include mechanical interlocking verification, high-voltage power frequency withstand tests, circuit resistance measurements, partial discharge testing, and functional checks of protection relays and motorized mechanisms. Witnessed testing by third-party inspectors (SGS, BV, TUV) is supported.

 

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As one of the most experienced ring main unit manufacturers and suppliers in China, we also support customized service. We warmly welcome you to buy high quality ring main unit from our factory. If you have any enquiry about pricelist, please feel free to email us.