Atmospheric Pressure Sealed Nature-Air Insulated RMU/Switchgear (SR-17.5kV)
Atmospheric Pressure Sealed Nature-Air Insulated RMU/Switchgear (SR-17.5kV) Atmospheric Pressure Sealed Nature-Air Insulated RMU/Switchgear (SR-17.5kV)
Atmospheric Pressure Sealed Nature-Air Insulated RMU/Switchgear (SR-17.5kV)

ASNA RMU/Switchgear（SR-17.5kV）

The atmospheric pressure sealed nature-air insulated ring main unit (RMU) utilizes an innovative, world-first technology where the primary conductive circuit is enclosed in a sealed cabinet with atmospheric air pressure. The fully sealed, air insulated system ensures stable operation without the risk of gas leaks. With no need for regular cleaning or gas monitoring, and no operational interruptions for gas refills or equipment replacement, this RMU significantly reduces maintenance requirements. Its single-phase insulation structure also eliminates the risk of electrical faults, ensuring safe and reliable operation.

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Technical Specifications:

  • Rated Voltage: 17.5kV
  • Rated Current: 630A

What is an atmospheric pressure air insulated 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.
Technical Parameters
Item Unit Parameter
Rated Voltage (Ur) kV 17.5
Rated Frequency (Fr) Hz 50, 60
Rated Currenct (Ir) A 630
Rated Insulation Level Short-time Power-frequency Withstand Voltage (Ud) kV 38/45
Lightning Impulse Withstand Voltage (Up) kV 95/110
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 Voltage (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.

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 air insulated RMU 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.

HM POWER has long been engaged in the development and manufacture of smart grid power distribution equipment. With a focus on simplicity, reliability and safety, our fully sealed air insulated ring main units are trusted by customers around the globe. In order to guarantee that the air insulated switchgears are engineered and built to the highest standards of quality, our team of professionals, who have decades of experience in power distribution, strives for breakthrough technology to ensure that every product we supply is of premium quality.
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