Reliable SF6 Gas-Insulated RMU Manufacturer for Efficient Medium Voltage Switchgear

SF6 Gas-Insulated Ring Main Unit Technical Overview and Product Parameters

Medium-voltage secondary distribution networks require switching equipment that combines compact footprint, reliable operation, and a high level of personnel safety. The SF6 Gas-Insulated RMU fulfills these demands by housing all live switching and busbar components inside a sealed stainless steel tank filled with sulfur hexafluoride gas. Raydafon Group manufactures a comprehensive range of SF6 Gas-Insulated RMUs for 12 kV, 24 kV, and 36 kV systems, covering both indoor and outdoor installations. These units are widely used in utility distribution networks, industrial plants, commercial buildings, renewable energy systems, and infrastructure projects where space is limited and reliability cannot be compromised.

Raydafon Group designs each SF6 Gas-Insulated RMU as a sealed-for-life system. The main switching functions, busbar connections, and cable compartments are insulated and cooled by SF6 gas at low pressure. This design eliminates the need for routine gas handling, reduces maintenance intervals, and protects internal components from moisture, dust, and pollution. The result is a switchgear solution that delivers stable performance for more than 30 years under normal operating conditions. The following sections provide a detailed breakdown of the technical parameters, configuration options, and application benefits of the Raydafon SF6 Gas-Insulated RMU product family.

Product Architecture and Core Design Features

Raydafon Group builds the SF6 Gas-Insulated RMU around a modular stainless steel tank that is laser-welded and filled with SF6 gas at a rated pressure of 0.4 bar gauge at 20 °C. Each functional unit, such as a load break switch, circuit breaker, or busbar section, is housed in its own gas compartment. This compartmentalized architecture allows operators to isolate a single switching device without affecting adjacent feeders. The cable compartment is separate from the gas tank and is fitted with front or rear access panels, depending on the installation requirements.

The primary switching elements include SF6 load break switches, vacuum circuit breakers, and earthing switches. Load break switches are designed for frequent operation and can interrupt load currents up to the rated normal current of the unit. Vacuum circuit breakers handle short-circuit interruption and are available with protective relays for transformer, feeder, or incoming protection. Earthing switches with full short-circuit making capacity are interlocked with the corresponding load break switch or circuit breaker to prevent unsafe operations.

Key design features of the Raydafon Group SF6 Gas-Insulated RMU include:

• Sealed stainless steel tank with laser-welded construction for gas tightness and corrosion resistance
• Separate gas compartments for each switching function to improve operational flexibility
• Internal arc classified design according to IEC 62271-200 for enhanced operator safety
• Maintenance-free primary circuit with no need for gas refilling over the entire service life
• Front-operable cable compartments with integrated voltage detection systems
• Compact dimensions suitable for pad-mounted, wall-mounted, or free-standing installations
• Optional motorized operation and remote terminal unit integration for smart grid applications
• Wide operating temperature range with optional low-temperature kits for cold climates

Detailed Electrical Parameters

The Raydafon Group SF6 Gas-Insulated RMU is available in three standard voltage classes. The tables below present the main ratings and test results according to IEC 62271-1, IEC 62271-200, and IEC 62271-102. All values are verified through type tests conducted in accredited laboratories.

Electrical Ratings

Switching Device Ratings

Mechanical and Environmental Parameters

Raydafon Group engineers the SF6 Gas-Insulated RMU for robust performance in a wide range of environmental conditions. The enclosure is fabricated from stainless steel and coated with a weather-resistant finish. The gas tank is designed to withstand internal arc pressure without rupturing, and the cable compartment provides adequate space for stress cones, surge arresters, and current transformers.

Mechanical Specifications

Operating Conditions

• Ambient temperature range: -25 °C to +55 °C, with optional low-temperature kit for -40 °C operation
• Relative humidity: up to 100% non-condensing
• Altitude: up to 1000 m without derating; higher altitudes on request
• Seismic withstand: 0.5 g ground acceleration according to IEC 62271-207
• Pollution degree: Class IV outdoor according to IEC 60815

SF6 Gas System Parameters

The SF6 gas system in the Raydafon Group SF6 Gas-Insulated RMU operates at low pressure and is designed for a sealed lifetime. Gas pressure is monitored by a temperature-compensated pressure gauge or a density sensor with alarm contacts. If the pressure drops below the alarm threshold, a signal is transmitted to the supervisory system, allowing planned intervention without interrupting service.

Gas System Ratings

Typical Configurations and Feeder Functions

The modular construction of the Raydafon Group SF6 Gas-Insulated RMU allows a wide variety of configurations to match different network topologies. Each functional module can be a load break switch, a vacuum circuit breaker, or a direct busbar connection. The following list gives the most common combinations used in secondary distribution:

• 2-way configuration: Two load break switches for loop-in and loop-out, ideal for compact ring main sections.
• 3-way configuration: Two load break switches plus one transformer protection circuit breaker, suitable for single transformer substations.
• 4-way configuration: Three load break switches plus one circuit breaker, often used for dual transformer or auxiliary feeder applications.
• 5-way configuration: Four load break switches plus one circuit breaker, for larger ring networks with multiple outgoing feeders.
• Metering configuration: Dedicated current and voltage transformer compartments for revenue metering or network monitoring.
• Bus riser configuration: Direct busbar connection for coupling two RMU units or extending an existing switchboard.

Each load break switch can be equipped with a motorized operating mechanism for remote switching. Vacuum circuit breakers can be fitted with microprocessor-based protection relays supporting overcurrent, earth fault, and directional protection functions. Raydafon Group also provides integration with SCADA, distribution automation, and smart grid platforms through standard communication protocols such as IEC 61850, Modbus RTU, and DNP3.

Safety and Interlocking System

The Raydafon Group SF6 Gas-Insulated RMU incorporates a comprehensive mechanical interlocking scheme to prevent hazardous operations. The interlocking logic follows the requirements of IEC 62271-200 and local utility standards. Key safety features include:

• Load break switch and earthing switch interlock: The earthing switch can be closed only when the corresponding load break switch or circuit breaker is in the open position.
• Circuit breaker and earthing switch interlock: The circuit breaker must be open before the earthing switch can be operated, and vice versa.
• Cable compartment access interlock: Access panels can be opened only when the earthing switch is closed and the cable is proven dead by an integrated voltage detection system.
• Gas pressure interlock: If SF6 pressure falls below the minimum operating level, the switching operation is blocked to prevent internal flashover.
• Padlock provisions: All operating handles accept padlocks for lockout-tagout procedures during maintenance.

Application Areas for Raydafon Group SF6 Gas-Insulated RMU

The compact and sealed design of the SF6 Gas-Insulated RMU makes it suitable for a broad range of installation environments. Raydafon Group units are currently in service across distribution utilities, industrial parks, data centers, hospitals, airports, underground railway systems, and renewable energy plants. The main application areas include:

• Secondary ring main distribution networks in urban and suburban areas
• Transformer substations for commercial and residential buildings
• Wind farm collection grids and photovoltaic power plant switchgear
• Industrial plant medium-voltage distribution and motor feeder protection
• Mining operations where dust and humidity resistance is critical
• Underground and tunnel installations where space is limited
• Port and harbor electrical infrastructure with high corrosion resistance requirements
• Temporary or mobile substations due to compact dimensions and light weight

FAQ: SF6 Gas-Insulated RMU

What is an SF6 Gas-Insulated RMU and how does it work?

An SF6 Gas-Insulated RMU is a type of medium-voltage switchgear used in ring main distribution systems. It encloses all primary switching contacts, busbars, and earthing switches inside a sealed steel tank filled with sulfur hexafluoride gas. The gas acts as an insulating medium and arc-quenching agent. When a switching operation occurs, the SF6 gas rapidly extinguishes the arc between contacts, allowing the switch to interrupt load or fault currents safely. Because all live parts are inside a sealed metal enclosure, the unit is safe for operators and resistant to environmental contamination.

Why is SF6 gas used in RMUs instead of air or solid insulation?

SF6 gas has excellent dielectric strength, approximately three times that of air at the same pressure, and superior arc-quenching properties. This allows the RMU to be much smaller than air-insulated switchgear while maintaining high voltage withstand capability. SF6 also has good thermal conductivity and is chemically stable, non-flammable, and non-toxic under normal operating conditions. These properties make it ideal for sealed-for-life switchgear where compact size and long maintenance-free service are required. Raydafon Group uses only high-purity SF6 gas that meets IEC 60376 specifications.

What are the typical applications for Raydafon SF6 Gas-Insulated RMUs?

Raydafon Group SF6 Gas-Insulated RMUs are designed for secondary distribution networks operating at voltages from 12 kV to 36 kV. Typical applications include utility ring main units, transformer substations, industrial feeder protection, wind and solar power collection systems, commercial building power distribution, and infrastructure projects such as airports, tunnels, and data centers. The compact size and sealed enclosure make them especially suitable for locations with space constraints, high humidity, dust, or salinity.

How often does the SF6 gas need to be refilled?

Under normal operating conditions, the SF6 gas inside a Raydafon Group SF6 Gas-Insulated RMU never needs to be refilled. The gas tank is sealed by laser welding and tested for a maximum annual leakage rate of 0.1 percent. Over a 30-year service life, the total gas loss remains well above the minimum operating pressure. If the pressure drops below the alarm threshold due to an abnormal condition, the unit sends a signal to the monitoring system, and a qualified service technician can perform a controlled gas refill or repair using standard SF6 handling equipment.

Is SF6 gas harmful to the environment or operators?

SF6 gas is non-toxic, non-flammable, and does not present a direct health risk to operators when handled according to IEC 62271-4 guidelines. However, SF6 is a potent greenhouse gas with a high global warming potential. For this reason, Raydafon Group designs its SF6 Gas-Insulated RMU as a sealed-for-life system with an annual leakage rate of 0.1 percent or less, minimizing emissions over the product life cycle. At the end of life, the gas can be recovered and recycled using standard gas handling equipment, and the RMU can be safely dismantled for material recovery.

What configurations are available for the Raydafon SF6 Gas-Insulated RMU?

Raydafon Group offers a modular range of SF6 Gas-Insulated RMUs with 2-way, 3-way, 4-way, and 5-way configurations. Each way can be equipped with a load break switch, a vacuum circuit breaker, or a direct busbar connection. Standard combinations include two load break switches plus one circuit breaker, three load break switches plus one circuit breaker, and four load break switches plus one circuit breaker. Metering modules with current and voltage transformers can also be integrated. The modular design allows customers to select the exact number and type of functional units for their network topology.

Can the RMU be used in extreme weather conditions?

Yes. The standard Raydafon Group SF6 Gas-Insulated RMU operates reliably in ambient temperatures from -25 °C to +55 °C. An optional low-temperature kit extends the minimum operating temperature to -40 °C by using special low-temperature lubricants, seals, and reduced gas pressure settings. The stainless steel enclosure and IP67 gas tank protection allow outdoor installation in coastal, desert, and high-humidity environments. The unit is also tested for seismic withstand up to 0.5 g ground acceleration, making it suitable for earthquake-prone regions.

How is the RMU installed and commissioned?

The Raydafon Group SF6 Gas-Insulated RMU is delivered fully assembled and factory-tested. Installation involves mounting the unit on a level concrete pad or steel frame, connecting the medium-voltage cables through the cable compartment, and wiring the auxiliary control circuits. The unit does not require on-site gas filling or vacuum processing. Commissioning checks include verifying the mechanical interlocks, testing the pressure monitoring contacts, performing a dielectric withstand test on the cable connections, and confirming the operation of any protection relays. Raydafon Group provides a detailed installation and commissioning manual with each unit, and service engineers are available for supervision or turnkey installation.

What maintenance is required over the service life?

The primary circuit of the Raydafon Group SF6 Gas-Insulated RMU is maintenance-free. No lubrication, contact adjustment, or gas refilling is required under normal conditions. Recommended maintenance activities are limited to periodic visual inspections of the enclosure, verification of the gas pressure indication, checking the mechanical operation of switches and interlocks, and testing the auxiliary equipment such as relays, lamps, and heaters. A detailed inspection every five years and a major overhaul after 20 years, or 10,000 mechanical operations for circuit breakers, are sufficient to ensure continued reliable operation throughout the expected service life.

Does Raydafon Group provide customization and after-sales support?

Yes. Raydafon Group works closely with utilities, EPC contractors, and panel builders to deliver customized SF6 Gas-Insulated RMU solutions. Customization options include special cable entry directions, non-standard voltage and current transformer ratios, additional protection functions, custom color finishes, and communication protocols for smart grid integration. After-sales support includes installation supervision, commissioning, operator training, spare parts supply, and emergency repair services. Raydafon Group maintains a global network of service engineers and authorized distributors to support customers throughout the entire product life cycle.