What is Gas Insulated Switchgear (GIS)?

July 15, 20240

As the global demand for reliable and efficient power distribution continues to rise, the electrical industry has witnessed the emergence of a game-changing technology – gas insulated switchgear (GIS). Traditionally, air-insulated switchgear (AIS) has been the dominant solution, but the inherent limitations of air insulation have paved the way for the widespread adoption of GIS. This comprehensive article delves into the remarkable features and applications of GIS, highlighting its transformative impact on the power industry.

Schneider Electric Switchgear

Understanding Gas Insulated Switchgear

Gas insulated switchgear, or GIS, is a type of high-voltage switchgear in which the major components, such as circuit breakers and disconnectors, are enclosed within a metal housing. This enclosure is filled with a specific dielectric gas, typically sulfur hexafluoride (SF6), which provides exceptional electrical insulation both within a phase and between phases. Unlike traditional AIS, where air is the primary insulating medium, GIS leverages the superior dielectric properties of SF6 to achieve a more compact and reliable design.

Key Components of GIS

The heart of a GIS system comprises several critical components, each playing a vital role in the efficient and safe operation of the power grid:

1. Circuit Breaker (CB)

The CB acts as the primary switching and protection device, monitoring faults and instantly interrupting currents to isolate problematic sections. Its internal mechanism, driven by trip coils, responds precisely to control commands, ensuring the swift isolation of faulty circuits.

2. Earthing Switch (ES)

The ES safely connects the busbars to the grounding grid whenever sections are de-energized for maintenance work. This feature limits voltage stresses on equipment during earth fault conditions.

3. Filter Earthing Switch (FES)

The FES is an enhanced version of the ES, designed to filter and limit transient recovery voltages, thereby reducing over-voltages during automatic grounding and ground release operations.

4. Disconnecting Switch/Disconnector (DS)

The DS isolates the main energized busbars from individual feeders, transformers, and circuit breakers that require maintenance, ensuring a safe and controlled work environment.

5. Current Transformer (CT)

CTs step down high currents to lower, easily measured values, enabling current monitoring, metering, and the initiation of protective relaying.

6. Potential Transformer (PT)

PTs lower system voltages to standardized nominal voltages that can be measured by instruments, facilitating voltage monitoring, relaying, and the metering of power parameters.

36 kv GIS
36 kV GIS

Advantages of Gas Insulated Switchgear

The superior design and construction of GIS offer a multitude of advantages that have made it a preferred choice in the power industry:

1. Compact Size

The compact nature of GIS, with its components sealed within a metal housing, allows for a significantly smaller installation footprint compared to traditional AIS. This space-saving feature is particularly beneficial in densely populated urban areas or where land is scarce.

2. Enclosed Design

The fully encapsulated GIS design shields the live equipment from environmental stresses, such as humidity, dust, corrosion, and radio interference. This enhanced protection ensures consistent service continuity and extends the lifespan of the equipment.

3. High Reliability

The stable insulating properties of SF6 gas, maintained through regulated pressure and temperature, result in impressive annual reliability. GIS systems are highly resistant to faults, even under severe climatic conditions and system disturbances.

4. Long Lifespan

The SF6 gas completely isolates the internal components from oxygen and moisture, preventing tank corrosion and part degradation. This translates to a remarkably long usable life for GIS, often exceeding 30 years, with minimal maintenance requirements.

5. Enhanced Safety

Unlike air, SF6 gas is non-flammable and does not support combustion, effectively eliminating the risk of fire hazards. This feature, combined with the minimal maintenance needs, significantly enhances the safety of GIS substations for both equipment and personnel.

Schneider Electric Gas Insulated Switchgear
Schneider Electric Gas Insulated Switchgear

Applications of Gas Insulated Switchgear

The versatility and advantages of GIS have made it a preferred choice across a wide range of applications in the power industry:

1. Industrial Townships

GIS is extensively utilized in heavy industries, such as petrochemical plants, where uninterrupted power supply is critical and space is at a premium.

2. Hydroelectric Stations

The compact nature of GIS enables optimized substation layouts in hydroelectric power stations, which are often located in remote, mountainous areas alongside reservoirs and dams.

3. Underground Substations

In densely populated city centers, GIS allows for the installation of minimal-footprint substations underground, beneath roadways and buildings, minimizing the impact on urban landscapes.

4. City Building Extensions

As cities expand vertically with the construction of new high-rise buildings, GIS supports reliable power distribution through elevated ring main units that occupy a small footprint.

5. Offshore and Onshore Wind Power Connections

GIS plays a crucial role in the integration of renewable energy sources, such as offshore and onshore wind power, by providing a reliable and compact solution for power transmission and distribution.

The use of gas-insulated MV switchgear is important for safety.
The use of gas-insulated MV switchgear is important for safety.

Comparison: Air Insulated Switchgear vs. Gas Insulated Switchgear

When selecting the ideal switchgear for a project, it is essential to consider the key differences between AIS and GIS. These distinctions can significantly impact the overall performance, installation, maintenance, and total ownership cost of the system.

Construction

AIS utilizes air as the insulating medium within a metal-clad structure, while GIS employs the superior dielectric properties of SF6 gas. The GIS system’s hermetically sealed breakers are a “sealed-for-life” technology, unlike the AIS breakers, which can be dismantled for service and troubleshooting.

Installation

GIS systems are substantially lighter and more compact than their AIS counterparts, allowing for quicker and easier installation. The reduced footprint of GIS can translate to a 40% smaller physical footprint compared to AIS.

Operation

GIS systems provide front access, making them more user-friendly and safer for regular operation. The fully insulated and shielded components in GIS also minimize the risk of arc flash events, enhancing the overall safety of the system.

Maintenance

GIS requires significantly less maintenance compared to AIS. GIS systems typically only need visual inspections every five years or more, while AIS requires more frequent inspections and maintenance, often involving several hours of work every two years.

Total Ownership Cost

Although the initial investment in GIS is higher, typically 10% to 40% more than AIS, the long-term cost savings in maintenance and reduced downtime make GIS a more economical choice over the equipment’s lifespan.

Gas insulated switchgear has emerged as a transformative technology in the power industry, offering a compelling solution to the limitations of traditional air-insulated switchgear. With its compact size, enhanced reliability, extended lifespan, and improved safety features, GIS has become the preferred choice for a wide range of power distribution applications, from industrial complexes to urban centers and renewable energy integration.

36 kV Air Insulated Switchgear

As the global demand for reliable and efficient power continues to grow, the adoption of GIS technology will play a pivotal role in shaping the future of the power grid. With Vekmar expertise and innovative GIS offerings, power utilities and industrial consumers can unlock the full potential of this revolutionary technology, paving the way for a more sustainable and resilient power infrastructure.

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