Gas Insulated Switchgear: Definition, Components, and Applications

Contents

Gas-insulated switchgear (GIS) is a type of electrical equipment that uses a gas, such as sulfur hexafluoride (SF6), to insulate and protect various components of a power system. It consists of metal-enclosed compartments that house circuit breakers, disconnectors, bus bars, transformers, earth switches, surge arresters, and other devices. GIS is mainly used for medium and high voltage applications, where space is limited, and reliability is essential.

In this article, we will explain what GIS is, how it works, what are its advantages and disadvantages, and what are some of its common applications. We will also compare GIS with air-insulated switchgear (AIS), which is the conventional type of switchgear that uses air as the insulation medium. Finally, we will introduce some of the types and models of GIS available from different manufacturers.

What is Gas Insulated Switchgear?

A gas-insulated switchgear (GIS) is defined as a metal-enclosed switchgear that uses a gas, such as SF6, as the primary insulation between live parts and the earthed metal enclosure. The gas provides high dielectric strength, high thermal stability, and excellent arc quenching properties.

The main components of a GIS are:

Circuit breakers: These are devices that can interrupt the flow of current in an electrical circuit when a fault occurs. They use a vacuum or SF6 as the interrupting medium, depending on the voltage level and application.
Disconnectors: These are devices that can isolate a part of the circuit from the rest of the system for maintenance or testing purposes. They use SF6 as the insulation medium and can be operated manually or remotely.
Bus bars: These are conductors that connect different parts of the circuit, such as generators, transformers, feeders, etc. They use SF6 as the insulation medium and are arranged in a three-phase system.
Transformers: These are devices that can change the voltage level of an electrical circuit. They use SF6 as the insulation medium and can be either power transformers or instrument transformers (such as current transformers or voltage transformers).
Earth switches: These are devices that can connect a part of the circuit to the earth for safety or grounding purposes. They use SF6 as the insulation medium and can be operated manually or remotely.
Surge arresters: These are devices that can protect the circuit from overvoltages caused by lightning strikes or switching operations. They use SF6 as the insulation medium and can be either metal oxide varistors (MOVs) or spark gaps.

All these components are enclosed in a metal enclosure that is filled with SF6 gas at a certain pressure. The enclosure is divided into several compartments that are separated by gas-tight barriers. The compartments are connected by gas pipes and valves that allow gas flow and pressure control.

The enclosure is also equipped with sensors, monitors, indicators, alarms, and control devices that ensure the proper operation and safety of the GIS. The enclosure can be either indoor or outdoor, depending on the environmental conditions and design requirements.

How Does Gas-Insulated Switchgear Work?

The main principle of GIS operation is to use SF6 gas as an insulator and an arc extinguisher. SF6 gas has several advantages over the air as an insulation medium:

It has a higher dielectric strength than air, which means it can withstand higher voltages without breakdown.
It has a lower molecular weight than air, which means it has a higher thermal conductivity and can dissipate heat more efficiently.
It has a higher electronegativity than air, which means it can capture free electrons more effectively and reduce ionization in the arc.

These properties make SF6 gas ideal for GIS applications, where space is limited, and reliability is essential.

The operation of GIS can be explained by using an example of a three-phase circuit breaker. Under normal conditions, the circuit breaker contacts are closed and current flows through them. When a fault occurs in the circuit, such as a short circuit or an overload, the contacts separate, and an arc occurs between them.

The arc is composed of ionized gas that conducts electricity. The arc generates heat and pressure that can damage the contacts and other components. To prevent this, the arc must be extinguished as quickly as possible.

The arc extinction process in GIS involves two mechanisms: thermal interruption and dielectric interruption.

Thermal interruption: This mechanism relies on cooling down the arc by transferring heat to the surrounding gas. As the arc cools down, its resistance increases, and its current decreases until it reaches zero at a natural current zero crossing point. At this point, the arc is extinguished.

Dielectric interruption: This mechanism relies on increasing the dielectric strength of the gas by removing the ionized particles from the arc path. As the arc is interrupted, SF6 gas flows into the chamber and absorbs the free electrons, forming neutral molecules that do not conduct electricity. The dielectric strength of the gas recovers rapidly, preventing the arc from restriking.

After the arc is extinguished, the contacts close again, and the circuit is restored. The SF6 gas pressure is monitored and controlled by a gas management system, which also ensures gas quality and leakage detection.

Gas-Insulated Switchgear Applications

GIS is widely used in various applications due to its compactness, reliability, and low maintenance requirements. Some of the common applications of GIS are:

Urban or industrial areas: GIS is ideal for urban or industrial areas where space is scarce and pollution levels are high. GIS can be installed indoors or outdoors, on roofs, underground, or offshore platforms, without affecting the environment or aesthetics.
Power generation and transmission: GIS is used to connect power plants to the grid, as well as to transmit and distribute power over long distances and across different voltage levels. GIS can handle high currents and voltages, as well as provide protection and control functions for power systems.
Renewable energy integration: GIS is used to integrate renewable energy sources, such as wind farms or solar plants, into the grid. GIS can provide flexible and reliable connections, as well as voltage and frequency regulation for intermittent power generation.
Railways and metros: GIS is used to supply power to railways and metros, as well as to control and protect their electrical systems. GIS can reduce losses and improve efficiency, as well as provide safety and reliability for passengers and operators.
Data centers and factories: GIS is used to supply power to data centers and factories, where high-quality and uninterrupted power is essential for their operation. GIS can provide high availability, redundancy, and fault tolerance, as well as reduce electromagnetic interference and harmonics.

Gas Insulated Switchgear Vs Air Insulated Switchgear

Gas-insulated switchgear (GIS) has several advantages over air-insulated switchgear (AIS), which is the conventional type of switchgear that uses air as the insulation medium. Some of the advantages of GIS are:

Space saving: GIS can reduce the footprint of a substation by up to 90%, compared to AIS. This is because GIS can be installed in a single or multi-story building, or even underground, while AIS requires a large open area for installation and maintenance.
Safety: GIS can enhance the safety of personnel and equipment, as it eliminates exposure to live parts and arc flash hazards. GIS also reduces the risk of fire, explosion, or environmental contamination, as it contains SF6 gas in a sealed enclosure that prevents leakage.
Reliability: GIS can improve the reliability of the power supply, as it has fewer moving parts and joints that can wear out or fail. GIS also has a longer service life than AIS, as it is less affected by environmental factors such as humidity, dust, corrosion, or pollution.
Maintenance: GIS can reduce maintenance costs and downtime, as it requires less frequent inspection and testing than AIS. GIS also has self-diagnostic features that can detect faults and alert operators before they become critical.

However, GIS also has some disadvantages compared to AIS, such as:

Cost: GIS is more expensive than AIS in terms of initial investment and operation. This is because GIS requires more sophisticated technology and materials, as well as higher quality standards and testing procedures.
Complexity: GIS is more complex than AIS in terms of design and installation. This is because GIS requires more coordination and integration among different components and systems, such as gas management, protection, control, communication, etc.
Availability: GIS may have lower availability than AIS in some cases, especially when a fault occurs inside a compartment that affects multiple components. This is because GIS may require more time and effort to isolate and repair the fault than AIS.

Therefore, the choice between GIS and AIS depends on various factors such as site conditions, site conditions, technical specifications, economic factors, and personal preferences.

Advantages and Disadvantages of Gas-Insulated Switchgear

As mentioned before, GIS has several advantages over AIS, such as:

Space saving: GIS can reduce the footprint of a substation by up to 90%, compared to AIS. This is because GIS can be installed in a single or multi-story building, or even underground, while AIS requires a large open area for installation and maintenance.
Safety: GIS can enhance the safety of personnel and equipment, as it eliminates exposure to live parts and arc flash hazards. GIS also reduces the risk of fire, explosion, or environmental contamination, as it contains SF6 gas in a sealed enclosure that prevents leakage.
Reliability: GIS can improve the reliability of the power supply, as it has fewer moving parts and joints that can wear out or fail. GIS also has a longer service life than AIS, as it is less affected by environmental factors such as humidity, dust, corrosion, or pollution.
Maintenance: GIS can reduce maintenance costs and downtime, as it requires less frequent inspection and testing than AIS. GIS also has self-diagnostic features that can detect faults and alert operators before they become critical.

However, GIS also has some disadvantages compared to AIS, such as:

Cost: GIS is more expensive than AIS in terms of initial investment and operation. This is because GIS requires more sophisticated technology and materials, as well as higher quality standards and testing procedures.
Complexity: GIS is more complex than AIS in terms of design and installation. This is because GIS requires more coordination and integration among different components and systems, such as gas management, protection, control, communication, etc.
Availability: GIS may have lower availability than AIS in some cases, especially when a fault occurs inside a compartment that affects multiple components. This is because GIS may require more time and effort to isolate and repair the fault than AIS.

Therefore, the advantages and disadvantages of GIS should be weighed carefully before choosing the type of switchgear for a specific application.

Types and Models of Gas-Insulated Switchgear

There are different types and models of gas-insulated switchgear available from various manufacturers. Some of the common types are:

Isolated phase GIS: In this type, each phase of the circuit is assembled separately in its own compartment. This type requires more space than other types of GIS, but it prevents phase-to-phase faults.
Integrated three-phase GIS: In this type, all three phases of the circuit are assembled together in a single compartment. This type reduces the space requirement by one-third compared to isolated phase GIS.
Hybrid GIS: In this type, a combination of isolated phase and three-phase elements is used. This type provides a balance between space saving and fault prevention.
Compact GIS: In this type, more than one functional element is encapsulated in a single compartment. For example, a circuit breaker, a disconnector, and a current transformer can be combined in one module. This type reduces the space requirement further compared to other types of GIS.
Highly integrated system (HIS): In this type, all the substation equipment is encapsulated together in a single enclosure. This type provides a complete solution for an outdoor substation in a single unit. This type eliminates the need for external connections and reduces installation time.

Some examples of models of gas-insulated switchgear from different manufacturers are:

Siemens Energy: 8VM1 Blue GIS (up to 72.5 kV), 8VN1 Blue GIS (up to 145 kV), 8DQ1 Blue GIS (up to 550 kV), 8VQ3 Blue GIB (up to 420 kV), LPIT (low power instrument transformer) for compact and lightweight GIS design.
Hitachi Energy: ELK-04 C (up to 170 kV), ELK-14 C (up to 300 kV), ELK-3 C (up to 420 kV), ELK-04 D (up to 170 kV), ELK-14 D (up to 300 kV), ELK-3 D (up to 420 kV), ELK-04 F (up to 170 kV), ELK-14 F (up to 300 kV), ELK-3 F (up to 420 kV).
CHINT: XGN86 (gas insulated switchgear) (up to 40.5 kV), XGN15-12 (gas insulated switchgear) (up to 12 kV), XGN15-24 (gas insulated switchgear) (up to 24 kV), XGN74-12 (gas insulated switchgear) (up to 12 kV), XGN86-40.5 (gas insulated switchgear) (up to 40.5 kV).
ABB: ZX0.2 (gas-insulated switchgear) (up to 36 kV), ZX1.2 (gas-insulated switchgear) (up to 52 kV), ZX2 (gas-insulated switchgear) (up to 40.5 kV), ZX2.2 (gas insulated switchgear) (up to 52 kV), ZX1.5-R (gas insulated switchgear) (up to 24 kV), ZX1.5-G (gas insulated switchgear) (up to 24 kV), ZX0 block design (gas insulated switchgear) (up to 24 kV).

These are some of examples of gas-insulated switchgear models, but there are many more models and types available from different manufacturers around the world.

Conclusion

Gas-insulated switchgear is a type of electrical equipment that uses a gas, such as SF6, as the primary insulation and arc extinguishing medium. It consists of metal-enclosed compartments that house various components of a power system, such as circuit breakers, disconnectors, bus bars, transformers, earth switches, surge arresters, etc.

GIS has several advantages over air-insulated switchgear, such as space-saving, safety, reliability, and low maintenance. However, GIS also has some disadvantages, such as high cost, complexity, and lower availability in some cases.

GIS is widely used in various applications, such as urban or industrial areas, power generation and transmission, renewable energy integration, railways and metros, data centers, and factories. There are different types and models of GIS available from different manufacturers, depending on the voltage level and design requirements.

GIS is a modern and advanced technology that can provide efficient and reliable solutions for power systems. However, it is important to understand its characteristics, advantages and disadvantages, and applications before choosing the type of switchgear for a specific project.