Air-Insulated vs. Gas-Insulated RMUs: Which One Is Better?

It can be complicated to pick one RMU (Ring Main Unit) for your electrical distribution system as there are several options available in the market. Between Air-Insulated and Gas-Insulated RMUs, the system requirements, space availability, and even long-term expenditures can quickly overwhelm you. If you are facing concerns related to space, upkeep, and even environmental factors, having knowledge of the differences between these two RMUs becomes essential. This guide is aimed at giving you the necessary information to make the right choice for your business. So, keep reading!

1) What are Air-Insulated RMUs?

Air-insulated RMUs (Ring Main Units) are classified as switchgear systems in medium-voltage. These units also control, protect, and isolate electrical circuits. This equipment is often found in commercial buildings, power stations, factories, and residential complexes.

Air is used as the insulator in air-insulated RMU systems, which means that regular air surrounds all the live parts to ensure short circuits and other electrical faults do not occur. Additionally, air-insulated RMU systems are simple in design, which makes them easy to maintain. There is no need for special gases, extreme care, or even worrying about gas leaks.

Each unit is equipped with switches, circuit breakers, and fuses. All these elements yield synchronized operations to guarantee a power flow that is safe. The RMU has the means to disconnect power instantly in case of a fault/overload situation to protect the system from damage.

Air-insulated RMU works best in scenarios where cost-effectiveness is needed. Their affordability and low installation as well as long-term maintenance makes it easy to use. The RMU design also allows easy inspection and repair.

Despite these advantages, the units are larger than the gas-insulated ones, which increases the space required for installation. Moreover, the units may also have reduced efficiency in harsh areas that have severe pollution.

However, the units serve multiple functions for standard indoor and outdoor applications, making them useful. They can be the perfect solution if medium-voltage power management requires a device that is effective and uncomplicated.

2) What are Gas-Insulated RMUs?

Gas-insulated RMUs (Ring Main gear) are compact sealed units that are used for medium and high-voltage power distribution. These units utilize SF6 gas for insulation instead of using air. The insulating strength of this gas allows the RMU to be at high voltages in a small space because it is safely confined.

In an RMU, all live parts are contained in a metal tank with SF6 gas. This design protects the components from water, dust, chemicals, and other external damage. Due to this feature, gas-insulated RMUs are suitable for use in harsh environments such as tunnels, wind farms, coastal areas, basements, and even in the sea.

RMUs can be installed in places with limited space, such as commercial buildings, factories, and even in urbanized cities. Although they are small, compact, and lightweight, RMUs provide strong protection, high performance, and increased longevity.

Another advantage is that these units are low maintenance. Being sealed means that the parts are protected from the external environment, keeping them clean from dust, dirt, and damage. These units are also extremely dependable and can run for many years without issues.

And, one major drawback, however, is that SF6 gas needs to be handled with extra care. It poses a risk to the environment since it’s a potent greenhouse gas. Because of this, modern RMUs come equipped with gas monitoring systems to detect leaks and ensure safety.

3) Head-to-Head Comparison

When choosing between air-insulated and gas-insulated RMUs, it is crucial to analyze the differences in design, performance, and application. Below are a few major pointers that you should be aware of:

i) Insulation Material

The Air-Insulated RMUs are insulated using clean, natural air. The air is abundant and free, making it simple, safe, easy to manage and cost-effective.

SF6 gas, which provides much stronger insulation than air, is used in the Gas-Insulated RMUs. This enables a more compact design.

ii) Size and Spacing Requirements

Due to the lower effectiveness of air compared to SF6 gas as an insulator, the Air-Insulated RMUs are larger. Their installation space is also comparatively higher, which is a downside in congested regions.

Gas-insulated RMUs are much more compact. Their space efficiency allows for installation in urban systems, underground systems, or other areas where space is limited.

iii) Maintenance Requirements

Air-insulated RMUs require outside air to be operating, hence, they need constant checks. Their exposed environment causes performance factors such as dust, moisture, and temperature changes to impact the internals over time.

Gas-insulated RMUs have a sealing structure that protects their internal parts from contamination by external elements. This makes servicing less frequent, and less downtime is experienced. Hence, they are ideal for long-term operation when working in strenuous environments.

iv) Performance in Tough Conditions

Air-insulated RMUs do not perform well in high-pollution, saline, or humid areas. In general, the operational effectiveness of these devices is below par because of their environment and repairs are a necessity.

Gas-insulated RMUs stand strong against harsh conditions. Their protective seals shield sensitive components from moisture, dust, and pollution, enabling them to perform optimally during severe weather.

v) Environmental Considerations

Air-insulated RMU electrical units are more ecologically conscious as they do not use any harmful gases to the environment because they employ natural air as an insulator.

On the other hand, gas-insulated RMUs require some consideration because SF6 gas is a greenhouse gas. Although the gas is a good insulator, if there are leaks, it may have great effects on the environment. It is important to ensure that SF6 is monitored regularly to control the environmental risks.

vi) Cost and Investment

Air-insulated RMUs are usually more affordable at the point of purchase and during installation. Despite these initial cost advantages, their long-term maintenance burden due to constant environmental exposure along with frequent inspections may prove financially disadvantageous.

Due to the sealed design and SF6 gas component, Gas-Insulated RMUs have higher initial costs. However, in the long term, they are more cost-effective because these units are low maintenance, have fewer repairs, and have a longer service life because of their operational efficiency, even in extreme environments.

Feature	Air-Insulated RMU	Gas-Insulated RMU
Insulation Medium	Air	SF6 Gas
Size	Large	Compact
Maintenance	Regular cleaning needed	Low maintenance
Harsh Environment Use	Less suitable	Highly suitable
Environmental Impact	Eco-friendly	Needs gas control
Initial Cost	Lower	Higher
Long-term Cost	Possibly higher	Lower with fewer repairs

4) Delixi Gas-Insulated RMU

For effective and dependable power distribution, Delixi Electric provides gas-insulated RMUs powered by SF6 gas. These units employ SF6 gas for insulation and arc-extinguishing, providing a compact build and high efficiency.

• Key Models:

a) CDRM6-12/24KV SF6 GIS Metal Enclosed Switchgear

This model CDRM6-12/24KV has a modular structure, offering a combination of many scopes for its contained configuration. It is adaptable to many industrial and civil applications, from cable ring power networks to the terminals of a power supply. A fully sealed structure ensures safety while minimizing maintenance.

b) XGN20-12L/630-25 Indoor Medium Voltage SF6 Ring Main Unit

This RMU is designed to operate indoors and provides a compact and dependable solution for ring networks and dual radiation power supply systems. It uses modern sensor technologies and relay protection devices to increase safety during operation.

c) CDL8 Series Indoor Cubicle Type Gas Insulated Switchgear (C-GIS)

These models are efficient for space-saving and are best featured for medium voltage use. It employs gas insulation technology, guaranteeing safety and performance.

Advantages of Delixi Gas-Insulated RMUs:

+ Compact Design: Delixi Gas-insulated RMUs are ideal for installation where space is limited due to their compact dimensions attained from the use of SF6 gas.

+ Enhanced Safety: Operator safety is improved because the risk of faults is reduced in fully sealed metal enclosing structures. The design features also provide protection against environmental factors that increase the risk of damage, therefore safeguarding internal components.

+ Reduced Maintenance: Decreased maintenance and longer lifespan are results of the sealed design features that protect against exposure to contaminants.

+ Ethical Considerations: While SF6 aids in insulation, it is a greenhouse gas that needs to be handled with care. Delixi focuses on constructing devices that reduce emission leaks to protect the environment.

You can view RMU-related information on our webpage for further details regarding Delixi's gas-insulated RMUs.

5) How to Choose Between AIR and GIS RMUs?

A selection of Air-induced (AIR) or Gas-induced (GIS) ring main units (RMUs) revolves around the specifics of your projects. Attention to detail is critical when making this choice. To assist, we have crafted this guide:

a) Availability of Space

In comparison to GIS RMUs, AIR RMUs certainly require more space. In case space is limited for installation, AIR RMUs may not be suitable based on your preferences.

In contrast, GIS RMUs are compact and ideal for areas with space constraints, such as urban environments and even underground installations.

b) Conditions of the Environment

As described before, AIR RMUs are more suitable for “clean” spaces that have low humidity and negligible dust. A high level of pollution, coupled with moisture, can severely obstruct the performance of these units.

On the other hand, GIS RMUs are better equipped for rugged environments. Extreme conditions such as heightened moisture or moisture can't interfere with their enclosed components. Hence, they are ideal for outdoor conditions.

c) The Maintenance Required

You often see that AIR RMUs have hidden costs, one of these being maintenance that includes regular cleaning due to parts being exposed to the air. The cost of cleanliness coupled with heightened operational requirements exceeds that of upkeep.

They require less maintenance due to their sealed design, which protects the components from environmental factors. This reduces the time and effort required for frequent inspections.

d) Cost Considerations

AIR RMUs have lower upfront costs, though they are often more expensive in the long run because of the frequent maintenance they require.

In contrast, GIS RMUs have a higher initial cost but become more economical over time due to reduced maintenance costs and a longer lifespan.

So, choosing between AIR and GIS RMUs relies on considerations such as space for the unit, environmental factors, maintenance, and budget. For a clean environment, GIS RMUs are cost-effective, but AIR RMUs are better for harsh conditions.

6) Conclusion

To summarize, both air-insulated and gas-insulated RMUs have their particular benefits depending on your requirements. The disadvantages of space and maintenance for AIR RMUs are mitigated by their cost-effectiveness and eco-friendliness. On the other hand, GIS RMUs are less cost-efficient but perform excellently in limited space and more hostile environments with harsh, long-term reliability and low maintenance needs. Think about how much space you have, the environment, and your budget, and select the right RMU for your project.