Metal-Clad vs. Gas-Insulated Switchgear: Which Is the Right Choice?
13/08/2025
Introduction
The power system is the backbone of modern society, and switchgear is at the heart of these systems. It is a combination of devices used to control, protect, and isolate electrical equipment. Without it, the power grid would be unable to handle faults and overloads, risking collapse.
As demands for safety, reliability, and efficiency continue to rise, switchgear technology has undergone continuous evolution. Today, the two most common types of switchgear in the medium-voltage field are metal-clad switchgear and gas-insulated switchgear (GIS).
Although these two devices share similar functions, their designs and underlying technical principles are fundamentally different. Therefore, gaining a thorough understanding of their characteristics is crucial for making the right choice based on specific application scenarios.
What Is Metal-Clad Switchgear?
In simple terms, a metal-clad switchgear cabinet is a type of switchgear cabinet that houses all core electrical components, such as circuit breakers, busbars, and transformers, in separate, individually grounded metal compartments.
This design is highly ingenious, with its core principle being that even if an issue arises in one compartment—such as a short circuit—the fault will not easily spread to other sections, significantly enhancing the equipment’s safety and reliability.
It is worth noting that the term “metal-clad” itself signifies this robust, compartmentalized structure. This is a very specific and stringent standard, distinct from the more general term “metal-enclosed,” which does not impose the same high requirements as “metal-clad.”
Working Principle
In metal-clad switchgear cabinets, air or insulating gases such as SF6 are typically used as the primary insulating material. In the event of a fault, the circuit breaker trips in a dedicated compartment, cutting off the current. Each component has its own compartment, combined with grounded metal barriers, to achieve both physical and electrical isolation. This allows us to perform safe maintenance on a specific part of the switchgear while other sections can continue to operate under power, without affecting overall functionality.
Advantages of Metal-Clad Switchgear
Enhanced Safety: The compartmented design offers superior protection against internal faults. An arc flash event is more likely to be contained within its compartment, reducing the risk of injury to personnel and damage to adjacent equipment.
Ease of Maintenance: The draw-out design of the circuit breakers allows for easy removal and replacement. This simplifies maintenance and troubleshooting, often without needing to shut down the entire switchgear line.
Proven Technology: Metal-clad switchgear has been a industry standard for decades. It is a highly reliable and well-understood technology with a vast installed base and readily available spare parts.
Flexibility: The modular design makes it easy to add or reconfigure sections as power requirements change.
Disadvantages of Metal-Clad Switchgear
Large Footprint: The air insulation and robust metal compartments require significant physical space, making it a poor choice for installations with limited floor space.
Environmental Exposure: Although designed to be rugged, the components are still exposed to the ambient environment. Dust, moisture, and other contaminants can accumulate, potentially requiring more frequent cleaning and maintenance.
Higher Busbar and Connection Requirements: The open-air busbar connections can be a point of weakness, and they also contribute to the overall larger size.
Applications
Metal-clad switchgear is commonly found in industrial plants, public substations, power plants, and large commercial buildings. It is an ideal choice for situations where space is not particularly limited but safety isolation and maintenance requirements are high.
What Is GIS Switchgear?
Gas-Insulated Switchgear (GIS) represents a more advanced and compact technology. In a GIS system, all live electrical components are contained within sealed, pressurized metal enclosures filled with a high-dielectric gas, most commonly sulfur hexafluoride (SF6).
Working Principle
The core of GIS technology is the use of SF6 gas as an insulating medium. SF6 has three times the dielectric strength of air, meaning it can withstand higher voltage pressures and is less prone to breakdown. This is why the entire switchgear can be significantly reduced in size. It has a sealed, positively pressurized housing that protects internal components from environmental influences, ensuring stable and reliable operation. In the event of a fault, the circuit breaker operates in an SF6 gas environment, enabling rapid cooling and arc extinction to ensure safety.
Advantages of GIS Switchgear
Compact Size: This is the most significant advantage of GIS. The superior insulating properties of SF6 gas allow for a footprint that is often 10% of that required by conventional air-insulated or metal-clad switchgear. This makes GIS ideal for urban areas, indoor substations, and offshore platforms where space is at a premium.
Exceptional Reliability: The sealed, pressurized design protects the internal components from moisture, dust, pollution, and rodents. This leads to a much lower failure rate and longer operational life.
Low Maintenance: Due to the sealed environment, GIS requires very little maintenance. Routine checks are primarily focused on monitoring the gas pressure and density.
Environmental Protection: While SF6 is a potent greenhouse gas, the sealed design ensures that it is contained and not released into the atmosphere during normal operation. This minimizes environmental impact compared to older, more porous systems.
Disadvantages of GIS Switchgear
High Initial Cost: The specialized components, manufacturing processes, and gas handling equipment make GIS systems significantly more expensive to purchase and install than metal-clad switchgear.
Complex Maintenance: While maintenance is infrequent, it is also more complex. Any internal fault or issue requires specialized tools and expertise to open the sealed enclosure, and the SF6 gas must be properly handled and reclaimed.
Environmental Concerns with SF6: Although contained, the potential for SF6 leakage or release during decommissioning is a major environmental concern. There is ongoing research and development into alternative insulating gases.
Noisier Operation: GIS circuit breakers tend to operate at a higher noise level compared to their metal-clad counterparts.
Applications
GIS switchgear is the preferred choice for high-voltage applications in urban substations, power plants, and offshore wind farms where space is severely limited. It is also increasingly used in industrial settings and commercial buildings where a high degree of reliability and low maintenance are paramount.
Metal-Clad vs. GIS: Key Differences
Feature
Metal-Clad Switchgear
Gas-Insulated Switchgear (GIS)
Size & Footprint
Large, requires significant floor space.
Compact, often 10% of the size of metal-clad. Ideal for confined spaces.
Maintenance
Routine maintenance required (e.g., cleaning, inspection) but is relatively easy due to the draw-out design.
Low-maintenance, sealed system. Internal repairs are complex and require specialized tools.
Initial Cost
Lower initial cost compared to GIS.
High initial cost due to specialized technology and materials.
Insulation Medium
Air or other gases (e.g., SF6) for insulation.
SF6 gas as the primary insulation medium.
Environmental Protection
Components are exposed to the ambient environment. Requires a clean operating space.
Sealed enclosure protects components from dust, moisture, and pollution.
Fault Isolation
Excellent fault containment within compartments.
Excellent fault containment within the sealed enclosure.
Busbar Design
Air-insulated busbars; takes up more space.
Gas-insulated busbars; highly compact.
1. Size and Footprint
Metal-Clad Switchgear: This type uses air as its primary insulation medium. Because air has a relatively low dielectric strength, more physical space is needed to maintain the required clearances between live components and grounded parts. This results in a large, bulky design, often taking up a considerable amount of floor space.
Gas-Insulated Switchgear (GIS): GIS leverages the superior dielectric strength of SF6 gas, which is up to three times greater than that of air. This allows the spacing between components to be drastically reduced, with all parts contained within a compact, sealed enclosure. The result is a much smaller footprint, often 10% or less of the size of a comparable metal-clad unit. This is a critical advantage for urban substations or industrial facilities where real estate is expensive and limited.
2. Maintenance
Metal-Clad Switchgear: Maintenance is a key aspect of metal-clad systems. The draw-out design of the circuit breakers allows for easy removal and inspection. Maintenance personnel can safely work on a single breaker or section of the switchgear while the rest of the system remains energized. However, due to the open-air design, components are exposed to environmental factors like dust and moisture, requiring more frequent routine inspections and cleaning.
Gas-Insulated Switchgear (GIS): GIS systems are renowned for being low-maintenance. The sealed, pressurized enclosure protects all internal components from environmental contamination, drastically reducing the need for routine cleaning and inspection. Maintenance is primarily focused on monitoring the gas pressure and density. While infrequent, any internal repairs are complex, requiring specialized tools and personnel to handle the SF6 gas and open the sealed chamber.
3. Initial Cost
Metal-Clad Switchgear: Generally, the initial purchase and installation cost of metal-clad switchgear is lower than that of GIS. The technology is well-established, and the manufacturing process is less complex than that of a high-pressure, sealed GIS system.
Gas-Insulated Switchgear (GIS): GIS has a significantly higher initial cost. This is due to the advanced technology, specialized manufacturing processes, and the cost of the SF6 gas itself. However, this higher upfront investment is often offset by the long-term benefits of reduced maintenance and a longer operational lifespan.
4. Environmental Protection
Metal-Clad Switchgear: While the equipment is housed in a metal enclosure, the components are still exposed to ambient conditions. This means the system can be affected by humidity, dust, and pollution, which can lead to flashovers or corrosion over time.
Gas-Insulated Switchgear (GIS): The sealed enclosure of GIS provides superior protection. It creates a controlled internal environment that is completely isolated from external pollutants, moisture, and even wildlife. This makes GIS ideal for harsh or polluted environments, and it contributes to the system’s high reliability and long life.
5. Insulation Medium
Metal-Clad Switchgear: The primary insulation medium is air, which has a lower dielectric strength. Some advanced metal-clad systems may use SF6 or other gases in the circuit breaker, but the overall busbar and component isolation often still relies on air.
Gas-Insulated Switchgear (GIS): The defining feature of GIS is its use of SF6 gas as the main insulation medium for all components. This allows for the compact design and provides exceptional insulation properties that resist electrical breakdown. While SF6 is a potent greenhouse gas, the sealed systems are designed to have extremely low leakage rates, minimizing environmental impact.
6. Fault Isolation
Metal-Clad Switchgear: The design of metal-clad switchgear is based on compartmentation. Each major component (e.g., circuit breaker, busbar, instrument transformer) is housed in a separate, grounded metal compartment. This design is highly effective at containing a fault within its specific section, preventing it from cascading and damaging the entire system.
Gas-Insulated Switchgear (GIS): GIS also offers excellent fault isolation. The entire system is housed in a single, sealed metal enclosure. When a fault occurs, the arc is quickly and efficiently extinguished by the pressurized SF6 gas, and the enclosure itself provides a robust barrier to prevent any external damage. The sealed nature of the system makes it nearly immune to external factors causing a fault.
Which Switchgear Is Right for You? Making the Choice
Choosing between metal-clad and GIS switchgear is a critical decision that depends on a variety of factors. There is no single “best” option; the right choice is the one that aligns best with your project’s specific requirements.
Here are some questions to consider:
Is space a critical constraint? If you have limited floor space, particularly in an urban or indoor setting, GIS is the clear winner.
What is your budget? If initial capital cost is a major concern, metal-clad switchgear is a more economical choice.
What are your maintenance capabilities? If you have a skilled team and want to perform routine, straightforward maintenance, metal-clad is a good fit. If you prefer a “set it and forget it” solution and can rely on specialized external support for any rare issues, GIS is the way to go.
What is the required reliability level? For mission-critical applications where downtime is unacceptable, the sealed, robust nature of GIS often provides a higher level of long-term reliability.
How sensitive are you to environmental concerns? While SF6 is a concern, modern GIS systems are highly engineered to prevent leaks. The robust construction and environmental containment may be a more compelling choice for some applications than a system exposed to external factors.
Conclusion
Metal-clad switchgear and gas-insulated switchgear (GIS) are both highly reliable and powerful protection and control technologies in power systems. Metal-clad switchgear features a robust structure, mature technology, and excellent cost-effectiveness, making it ideal for applications with limited space. GIS, on the other hand, is more compact, highly reliable, and easier to maintain, making it particularly suitable for modern environments with stringent space requirements.
At Chuanli, we understand that selecting the right switchgear is no simple task. We not only provide comprehensive metal-clad and GIS solutions but also offer professional consulting services to help you thoroughly analyze your needs and identify the most suitable technical solutions that maximize value for your project.