气体绝缘开关设备 (GIS)：全面概述

It is the GIS (Gas Insulated Switchgear), and that is all that matters. It is on the lips of every engineer wherever some sweat and tears result in power being delivered to those who need it. In the hectic world of electrical engineering, where not a square inch goes to waste and compromise on reliability is just not an option, the phrase has taken on drastically elevated importance. What is Gas Insulated Switchgear and why should you care if you’re an electrical engineer, project manager, or just a person who has to have his horizon widened into the infra world that makes this thing of ours work with its invisible little electrons skipping around the business?. Let’s explain what the gas-insulated switchgear is, how it works, and the fundamental importance for today’s modern power system.

什么是开关设备？

Before delving deep into the explanation of Gas Insulated Switchgear, let us explain what switchgear is. It includes an electric apparatus assembly used in controlling, protection and isolating circuits of electrical; it constitutes a very critical part of ensuring the safety and efficiency of power systems. Switchgear devices, some of the more common specimens being circuit breakers, fuses, contactors, and relays, form an integral part of the requirement both for controlling the flow of electricity to a small residential building and a large-scale industrial complex.

According to voltage levels, there are basically three kinds of switchgears:

• Low Voltage: Less than 1000 V AC.
• Medium Voltage: 1000-36 kV AC
• HV: Above 36 kV AC

Besides the voltage classifications, switchgear is also further differentiated by the type of insulation used in it. The commonest insulating media are: air, oil, and gas. And this is where gas-insulated switchgear comes into view.

What is Gas-Insulated Switchgear (GIS)?

Gas-insulated switchgear (GIS) is a metal-encapsulated compact switchgear that uses sulfur hexafluoride (SF6) gas as an insulating medium. Gas Insulated Switchgear being more compact and efficient compared to conventional air-insulated switchgears has hence found wide application in high-voltage applications in situations where space is limited.

SF6 gas has splendid insulating capability with excellent dielectric and arc-quenching performance. Therefore, based on this fact, without other difficulties, a GIS could therefore work safely and reliably under conditions where it would be impractical to operate other types of switchgear.

How Does Gas Insulated Switchgear Work?

The underlying principle of a Gas Insulated Switchgear is an insulation and cooling system that uses SF6 gas. The working principle is explained below.

• Insulation and Arc-Quenching: The Gas Insulated Switchgear system contains the components of the system hermetically within a sealed metal enclosure that is filled with SF6 gas. The SF6 gas easily quenches an arc when a fault in the electrical system causes the circuit breaker in the GIS to open and create an arc. This is because the SF6 gas can absorb free electrons, making it possible for it to neutralize an arc and hence extinguish it. This process happens very efficiently, hence making GIS very reliable.
• Compact Design: Due to the excellent insulating properties of SF6 gas, GIS units can be enormously small compared to their air-insulated counterparts. It is this compactness that makes the GIS ideal for urban areas or underground substations where land comes at a premium.
• Low maintenance: This is yet another unique feature of GIS. The sealed design ensures that entry to the system by contaminants is eliminated and thereby reduces frequent inspections and upkeep.

Why Use SF6 in GIS?

SF6 gas forms the basic building block of GIS, by virtue of a very unique property, which finds an application of prime importance for use at high voltages:

• High dielectric strength: The dielectric strength of SF6 is about three times air, making it highly potent against electrical breakdowns.
• Thermal Stability: SF6 can withstand high temperatures without breaking down, thus increasing the safety and durability of the switchgear.
• Arc Quenching Efficiency: Because SF6 can quench an arc very fast and recombine itself, it can be used time after time without appreciable degradation.

However, the fact that, though highly effective, SF6 happens to be a very potent greenhouse gas has to be taken into consideration. For this reason, managing and minimizing SF6 emissions is critically inherent in Gas Insulated Switchgear operations.

Components of Gas-Insulated Switchgear

Some of the major components that make up a GIS system include the following, all playing important roles in the functioning of the switchgear:

• Busbar: A conductor that interlinks various components within the Gas Insulated Switchgear to provide an efficient way of transmitting electricity.
• Current Transformer:This device steps down high currents to levels that will allow accurate measurement and monitoring.
• Circuit Breaker: The circuit breaker opens under fault conditions, thus saving a system from damage.
• Potential Transformer: The device is used, just like the current transformer, in stepping down the voltage levels for measurement.
• Cables: GIS cables are used for the transmission of electricity between switchgear and other equipment, either inside the GIS enclosure or outside.

Advantages of Gas-Insulated Switchgear

The advantages of GIS are plenty, making this a preferred application in many fields.

• Compactness: GIS units are way smaller than air-insulated switchgear, and this has a significant edge when space is at a premium, like in cities or industrial settings.

• Low Maintenance: Gas Insulated Switchgear requires less frequent maintenance, compared to traditional switchgear, due to its robust design and the use of SF6 gas.
• High Reliability: The SF 6 gas provides better insulation, and the sealed design allows it to be highly reliable with reduced risks of faults.
• Environmental Protection: This closed construction of Gas Insulated Switchgear minimizes the influence of dust, humidity, and other pollution on the device’s performance.

Disadvantages of Gas-Insulated Switchgear

Although GIS possesses many advantages, there are still some disadvantages associated with this technology. 

• Higher Cost: The initial cost of Gas Insulated Switchgear is higher than air-insulated switchgear. This can be attributed to the cost of the SF6 gas and the complex design.
• SF6-Gas-Management: SF6 is an ultra-powerful GHF gas, and even a little leakage or mismanagement can result in devastating consequences on the environment; hence, due care and mitigation strategies are required.
• Complex Installation: Setting up GIS requires specific competencies and equipment that can again increase the overall cost and time of the project.

Applications of Gas-Insulated Switchgear

GIS is extremely versatile, and its uses span a very wide spectrum of applications, including: Urban substations— The compact design of GIS makes it very suitable for use in urban substations where space is an issue.

• Industrial Facilities: GIS is generally used in industry where reliability and low maintenance are of prime concerns.
• Underground Substations: Since Gas Insulated Switchgear has a sealed design, this makes it quite suitable for underground installations where environmental factors can be more challenging.
• High-Pollution Areas: GIS does better in high-pollution areas; for example, beside seas or industries where the air-insulated switchgear might get contaminated.

结论

The requirement for effective, reliable, and compact electrical infrastructure will only increase as our cities grow and electricity demand increases. The gas-insulated switchgear is fit for all these challenges. Its compact design, high reliability, and low maintenance requirements make this technology an integral part in modern power systems.

Increasing sustainability, however, has to be coupled with SF6 emission management and the quest for alternative insulation gases that will help reduce the ecological footprint. In years to come, as technology advances, we will see further innovation in GIS, thus making it even a more indispensable tool in the electrical engineer’s arsenal.

Be it designing, installing, or operating electrical systems, knowledge of GIS and its place in modern power distribution is very important. As we hurtle into a more connected, electrified world, Gas Insulated Switchgear will no doubt be one of the cornerstones of our power infrastructure.

The paper aims to provide an overview on Gas-Insulated Switchgear: its importance, functionality, and areas of application, advantages, and challenges. Please feel free to ask any questions regarding aspects you would like to explore further.