Atmospheric Pressure Sealed Nature-Air Insulated RMU/Switchgear (SR-7.2kV/12kV) Manufacturer

Atmospheric Pressure Sealed Nature-Air Insulated RMU/Switchgear (SR-7.2kV/12kV)

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Nature is future

ASNA RMU/Switchgear（SR-7.2kV/12kV）

Atmospheric pressure sealed nature-air insulated RMU/switchgear offers a reliable alternative to traditional gas-insulated switchgear, using atmospheric pressure nature-air as the insulation medium. This innovative design eliminates the need for gas monitoring and system shutdown for gas-refilling, making it a low-maintenance solution. The atmospheric pressure sealed nature-air insulated system ensures stable operation without the risk of gas leaks or pressure drops.

The RMU features single-phase insulation, which enables easy fault isolation and prevents phase-to-phase arc faults without affecting the entire system, providing a safer and more reliable power distribution solution.

Technical Specifications:

Rated voltage: 7.2kV / 12kV
Rated current: 630A / 1250A

What’s Atmospheric Pressure Sealed Nature-Air Insulated Ring Main Unit (ASNA RMU)?

An Atmospheric Pressure Sealed Nature-Air Insulated Ring Main Unit (ASNA RMU) is a power distribution unit where the main electrical components are housed in a sealed cabinet, using air at atmospheric pressure as the primary medium of insulation. The design of this switchgear ensures a leak-proof, fully insulated and low maintenance operation, with key components like the vacuum interrupters, load break switches, and bus-bars enclosed safely. With their fully enclosed and insulated construction, RMUs minimize the risk of electrical faults, providing enhanced safety in environments for industrial, commercial, and residential applications where reliability and protection are critical.

With over 50,000 units operating worldwide for over a decade with proven safe, stable and fault-free performance, this power distribution unit works without SF₆, complying with the international trend. SF₆-free switchgear leads the development of sustainable RMU technology.

Advantages of Air Insulated RMU

World’s first atmospheric pressure sealed technology
The RMU uses a sealed air tank where the internal air pressure is equalized with external atmospheric pressure, eliminating the risk of gas leaks. This design doesn’t need gas replenishment or frequent maintenance, addressing the common issues found in traditional gas-insulated switchgear.
Aligned with global zero-carbon initiatives
By using atmospheric air instead of industrially produced gases, this RMU produces no greenhouse gas emissions and eliminates the need for gas recovery and disposal. Our RMU supports the global movement to phase out SF₆ gas, making it an environmentally responsible choice for sustainable power distribution.
Compact design
Despite being air-insulated, the RMU is designed to be as compact as traditional gas-insulated units, making it easy to replace older systems on-site. Its modular design helps to reduce overall project costs by minimizing space requirements and simplifying the installation process.
High environmental adaptability
The RMU has proven performance in diverse conditions, with extensive operational experience in environments with extreme temperatures, humidity, and dust. This makes it suitable for a wide range of global applications, ensuring reliable performance in challenging conditions.

Ensuring High Power Supply Reliability

Reinforced structural design
Our RMU is equipped with a pressure balance device inside the sealed air tank, which includes an air filtration system. This ensures that the air inside remains clean and unaffected by external pollutants like dust or salt fog, providing a controlled environment for the main circuit and ensuring continuous, reliable performance.
HSafe insulation system
Developed to operate reliably for 40 years under harsh conditions, our single-phase insulation system is designed with multiple layers of safety margins, eliminating the risk of phase-to-phase arc explosions. The casing and all internal non-conductive components are securely grounded. Since 2010, more than 50,000 units have been operating globally, with applications across Asia, Europe, and Africa without a single fault.
Reliable operating mechanism
The circuit breaker mechanism and the three-position isolator/grounding switch are designed for simplicity, compactness, and reliability. The breaker exceeds 10,000 mechanical operations, and the isolator/grounding switch has a lifespan of over 3,000 operations, ensuring long-term operational dependability.

Overall Dimension

1-bay
2-bay
3-bay

Unit	Length (mm)	Width (mm)	Height (mm)
1-bay	460	770	1640
2-bay	810	770	1640
3-bay	1160	770	1640

Differences among 1-bay, 2-bay and 3-bay

Structure
the difference depends on whether the primary conductive part shared an enclosure.
Function
2-bay equals a combination of two 1-bays, and 3-bay equals three 1-bays or one 1-bay and one 2-bay.

Size
2-bay is slightly smaller than a combination of two 1-bays, and 3-bay smaller than three 1-bays or one 1-bay and one 2-bay.
Price
1-bay is more costly compared with 2-bay or 3-bay evenly.

Applications

The Atmospheric Pressure Sealed Nature-Air Insulated RMU/Switchgear can be applied in several industries, such as airports, government buildings, ports, hospitals, data centers, commercial properties and transportation system.
Thanks to its small size and maintenance-free system, the RMU can be deployed in remote sites which demand more maintenance labour;
The Atmospheric Pressure Sealed Nature-Air Insulated RMU/Switchgear can also be transformed into street light box which supplies electricity to street lamps and stands as street decoration as night falls.

Item			Unit	Parameter
Rated Pressure (Ur)			kV	7.2	12
Rated Frequency (Fr)			Hz	50, 60
Rated Current (Ir)			A	630, 1250
Rated Insulation Level	Short-time Power-frequency Withstand Voltage (Ud)		kV	20/23	42/48
	Lightning Impulse Withstand Voltage (Up)		kV	60/70	75/85
Rated Short-time Withstand Current (Ik)			kA	20/25
Rated Short-circuit Duration（tk）			S	4
Rated Peak Withstand Current（Ip）			kA	50/63
Rated Short-circuit Breaking Current (Isc)			kA	20/25
Rated Short-circuit Making Current (Ima)		Vacuum interrupter	kA	50/63
		Earthing switch
Auxiliary Circuit and Control Circuit		Rated Pressure (Ua) DC/AC	V	≤400
		Power-frequency Withstand Voltage (1min)	V	2000
Mechanical Endurance		Circuit breaker	times	10000
		Disconnecting switch	times	3000
		Earthing switch	times	3000
Electrical Endurance		Circuit breaker	class	E2
		Earthing switch	class	E2
Degree of Protection by Enclosure				IP4X
Degree of Protection by Fully Sealed Tank				IP65

Normal Service Conditions

Maximum temperature	40℃ (average temperature ≤35℃ within 24h)
Minimum temperature	-25℃
Altitude	≤2000m
Daily average relative humidity	≤95%
Monthly average relative humidity	≤90%

Special Service Conditions

Provided the equipment should be run in special and harsh environment, please consult our experts.

Fundamental Units

SR series with following medium-voltage module function:

D (cable connection unit)
B (circuit breaker unit)
BB (circuit-breaker shared enclosure unit)
BBB (circuit-breaker shared enclosure unit)
M (medium-voltage metering unit)
PTX (PT unit)
BS (busbar sectionliser unit)
PT (PT unit)
PT (PT unit)
PTB (PT unit)

Note: "↠" and "↞" in the diagram are expandable kits.

Flexible combination can be customized as request. Please consult the manufacturer if you have any question.

More About Air Insulated RMU

How does the RMU ensures safe and reliable operation?

A:
First, the atmospheric pressure fully sealed system shields the RMU from external effects and guarantees the stable operation. Second, the switchgear’s single-phase insulating interior eliminates risks of internal arcing explosion. Third, the insulating medium inside the cabinet is air of atmospheric pressure which prevents the insulation performance from being weakened by pressure leak during the service life.
What is the status of Atmospheric Pressure Sealed Nature-Air Insulated RMU/Switchgear in China?

A:
In China, the atmospheric pressure sealed air insulated RMU has become a widely adopted solution within the power distribution networks of the country’s two largest state-owned grid companies: State Grid Corporation of China (SGCC) and China Southern Power Grid (CSG). Since its inclusion in their procurement catalog in 2017, the air insulated RMU has been recognized as a standard product, with both corporations making large-scale purchases each year. This marks a significant step forward in its adoption across the country, reinforcing its role as a reliable and environmentally friendly option for modern power distribution.
What is the installation requirement?

A:
The RMU can be mounted against wall and 80cm of space should be preserved in front of the cabinet for installation. The switchgear adopts lower incoming and lower outing of cable. Please contact us if you prefer other installation methods.
Is there any possibility of combining the HM POWER’s RMU with other brands’ switchgear?

A:
Combining switchgears of different brands is not advised, as they vary in plug and circuit and combining them may result in risks.

Switchgear Cabinet Baying

Voltage Withstand Test

Ring Main Unit Manufacturer

As a trusted manufacturer of ring main unit (RMU), HM POWER offers high quality Atmospheric Pressure Sealed Nature-Air Insulated RMU/Switchgear (up to 24kV) and reliable solutions for the smart grid power distribution industry. Our state-of-the-art technology and experienced team of experts ensure that our RMUs meet the highest standards of performance, reliability and safety.

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