What is gas insulated switchgear (GIS) and Principle of operation of GIS?

With today's rapidly growing urban population, space and power are becoming headaches. Due to their size and characteristics, gas insulated switchgear (GIS) is the optimal solution in such cases.

Compact, safe, and easy to maintain compared to Air Insulated Switchgear (AIS), GIS equipment is ideally suited for situations where substations need to be installed in limited space. In this article, we will introduce the definition, working principle, advantages, and applications of gas insulated switchgear（GIS） in detail.

What is gas insulated switchgear (GIS)?

Gas insulated switchgear(GIS) is a composite device encapsulated in a solid metal frame containing different types of electrical equipment, such as circuit breakers, busbars, transformers, earthing switches, and surge dischargers, which are immersed in sulfur hexafluoride (SF6) in a shielded compartment. A boundary is formed between the shielded compartment and the protection equipment.

The main functions of GIS are switching, separating, converting, measuring, and distributing electrical energy in power systems.GIS equipment is distinctive due to its use of SF6, an inert gas with exceptional chemical and thermal stability and insulating properties.

A GIS unit requires only a few centimeters of effective insulation distance compared to AIS equipment. It provides a higher level of reliability than AIS and is also cheaper to maintain as it takes up less space.

This equipment has been widely used since the early 1970s.

Principle of operation of GIS

GIS protects the power supply and distribution by interrupting the current in the circuit.

The circuit breaker contacts are normally closed, but when a fault occurs in the electrical system, they separate and arc.

The displacement of the active contacts is synchronized with the displacement of the valve that allows high-voltage SF6 to enter the arc chamber.

SF6 has the property of absorbing free electrons in the path of the arc, forming uncharged ions - because they become too heavy. The dielectric strength of the gas increases significantly, so the arc is extinguished.

When the arc is extinguished, the pressure of the SF6 decreases due to its ability to compound quickly. The SF6 is then stored in low-pressure tanks for subsequent use.

The attenuation of SF6 dielectric strength is greater than air insulation, making GIS the preferred choice for medium and high-voltage power systems.

Applications of GIS

Due to their compact, easy-to-integrate, and highly contamination-resistant armored construction, GIS substations are the obvious choice for installations in areas where space is limited or where exposure to high levels of contamination (dust, chemicals, salt layers, etc.) is a problem.

GIS applications cover:

◇ Industrial townships

◇ Hydroelectric power stations

◇ Underground substations

◇ Highly polluted areas

◇ Urban building extensions

◇ Offshore platforms

◇ Rooftops

◇ Railways

◇Power transmission

◇Renewable energy generation

◇Large cities with little space

◇Valleys

◇ Mountains

◇Industrial complexes

◇ High voltage transmission systems

GIS vs AIS: Comparison of advantages

The following table compares the characteristics of GIS and AIS equipment:

Gas Insulated Switchgear (GIS)

◇Designed according to IEC standards

◇Busbar insulation using SF6 media

◇ Switchgear using vacuum or SF6

◇Fixed switching

◇Small, compact dimensions

◇Low sensitivity to external factors

◇Low maintenance costs

◇Specific cable requirements

◇Air pressure can be monitored

◇Easy to install

◇ Quiet operation

◇Reduced operating costs

Air Insulated Switchgear (AIS)

◇Designed according to IEC standards

◇ Busbar insulation using air medium

◇ Switchgear using oil, air, vacuum or SF6

◇ Switchable on a fixed or design basis

◇Larger dimensions (tens of square meters)

◇Medium sensitivity to external factors

◇Medium maintenance costs

◇Variable cable requirements

◇ Only for switchgear that includes SF6 gas Monitorable air pressure.

◇Vulnerable to flying animals

◇Noisy operation

◇ Higher operating costs

GIS offers excellent performance and reliability. Thanks to its armored construction, which mitigates damage caused by the external environment, GIS is able to withstand interference from flying animals. This special design also makes GIS easier to maintain.

GIS is ideal for power supply and distribution in urban environments as well as in space-constrained and polluted environments such as industrial areas, sewers, and swamps.

Kexunan gas insulated switchgear

The gas-insulated switchgear provided by Kexunan Electrical Technology Co., Ltd. can meet the requirements of various users in the medium-voltage distribution system for ring network mode, combination mode, operating conditions, safety protection, transportation, and installation. By using extended busbars to connect the switchgear, a fully modular configuration is achieved to meet various standard and non-standard distribution schemes in the distribution network.

◆  Due to the use of hexafluoride, which has excellent insulation properties, Gas serves as an insulation and arc extinguishing medium. Thus, it can reduce the size of the switch cabinet and make it more compact, achieving small typing.

◆  High reliability and safety: The conductive part of the main circuit is sealed in SF6 gas, and the high-voltage live conductor is sealed and is not affected by changes in external environmental conditions, allowing the equipment to operate safely for a long time, with high reliability and no risk of electric shock or fire.

◆  Independent modular design, the air box is a high-precision aluminum plate that can be installed and detached, and the isolation switch adopts a three-station linear transmission. In order to reduce the clutter of control relays and circuits, a control module with nearly 100 PLC points is designed to achieve The grounding and isolation switches are all electric remote-operated. The modular design of the mechanism switch uses plum blossom fusion joints to connect the opening and closing points, which eliminates

the possibility of misoperation of the original rotary isolation switch and grounding switch and changes the contact of the original rotary isolation switch. To solve the problem of unstable and excessive resistance, a shielded voltage equalizing cover is installed outside each contact to completely solve the partial discharge problem in switch breakpoint production.

◆  Convenient application and layout of gas-insulated switchgear. As an independent unit, it can meet various main needs through combination. Wiring requirements. Delivered to the site in units, it can shorten the on-site installation period and improve reliability.

Advances in technology have made GIS devices more affordable and user-friendly, with sleek designs that allow for easy integration, inspection, and upkeep. Their streamlined construction and durable materials make them ideal for deployment in space-constrained environments that demand high levels of reliability, security, and functionality.