Electrical systems require switchgear to operate safely and effectively. If you’re looking to understand what is switchgear and its function, read below.
Switchgear forms a critical part of electrical installations. Learn what is switchgear here in this article, including its purpose in power distribution systems. Electrical switchgear is also classified based on various criteria such as voltage level and insulation medium, so we included that as well. In a nutshell, we have everything about switchgear explained.
What is Electrical Switchgear?
Switchgear is the collection of switching and safety devices mounted in one common structure and used to control, protect, or cut off circuits and equipment in an electrical system. In other words, it’s a series of circuit breakers, isolators, relays, fuses, and similar devices, assembled together. With switchgear, electrical systems provide a safe and reliable supply of electricity.
You can find different electrical switchgear in various types of power systems. These range from the low voltage 220V/240V lines used in domestic and commercial electricity systems to the high tension 1100kV lines used in power generation and distribution. Here is a summary of some of situations where switchgear is needed.
- Domestic power installations
- Commercial buildings to control power distribution
- In industrial environments to control power systems
- In utility facilities to run and control the grid.
- In systems that switch on large motors and generators
How Does Switchgear Work?
Now that you understand what it is, how does switchgear work? In order to shed more light on this kind of electric apparatus, it’s necessary to learn its operation. Let’s, therefore, see how switchgear works. Switchgear can provide for manual control. However, it mainly derives its usefulness from being able to work automatically.
For example, if a circuit breaker detects an overload, it will automatically disconnect the circuit. This protects the circuit from being damaged by the excessive current. Similarly, if a disconnect switch detects a fault, it will quickly interrupt the flow of electricity from the power supply.
These operations prevent circuits and equipment from being damaged during electrical faults. They also help to make electrical systems safe to humans. But that’s not all there is to how switchgear works. The most important part is that it only disconnects the faulty circuit, leaving the healthy ones working. This ensures continued availability of power to other loads within the system.
So, what is the function of switchgear in a power installation? As we have already seen, it controls the flow of electricity, protects against overloads, and isolates equipment from power surges, which makes it an essential part of electrical infrastructure. Here is a summary of its functions.
The main function of switchgear is to protect electrical equipment from damage due to overloading or short circuiting. Switchgear can also be used to control large electrical loads such as motors, where it provides for safe starting and running.
Switchgear is often used to isolate a piece of equipment for maintenance or repair. For example, if a switchgear isolator or disconnect switch is used to control a motor, technicians can switch it off to isolate the motor for maintenance purposes. Other instances include isolating circuits to test, fix, adjust, or upgrade an electrical system.
Switchgear and protection are inseparable terms: the equipment also ensures safe working environments for personnel. For example, circuit breakers are used to automatically disconnect circuits when an overload is detected. This helps to prevent injuries to people working on or near the circuit.
To have the various devices effectively perform their functions, manufacturers must ensure a few things during the switchgear design and fabrication steps. These include the following:
- Allowing for manual control
- Ensuring high reliability
- Fast switchgear operation
- Ability to discriminately isolate a faulty circuit
Switchgear equipment can be classified according to various criteria such as voltage level, location, and type of equipment. Other classification methods include grouping the switchgear by type of insulation utilized in the components, type of current, and more as explained below.
Switchgear Classification by Voltage
Based on voltage level, switchgear can be classified as low voltage (LV), medium voltage (MV), or high voltage (HV). That means a type of electrical switchgear for different installations or applications: more about these kinds of electrical switchgear below.
Low Voltage Switchgear
For this class of switchgear, low voltage means levels not exceeding 1,000 V AC (and up to 1500V DC). Low voltage switchgear is normally used in low voltage situations such as systems that control motor operations, in systems that feed low voltage switchboards, and so on. It mainly consists of miniature circuit breakers (MCBs), molded case circuit breakers (MCCBs), low voltage switches, and so on.
Medium Voltage Switchgear
Medium voltage switchgear, or MV switchgear, is a type of switchgear used to protect circuits and equipment that operate at voltages between 1 kV and 36 kV. You will mostly find MV switchgear in residential, commercial, and industrial electrical installations where it’s used to control power distribution. It’s also used in solar energy stations.
High Voltage Switchgear
High voltage switchgear, also called HV switchgear, includes switching devices for electrical systems that carry voltages above 36 kV. This kind of switchgear is typically used in utility applications such as substations. Due to the high voltages involved, arc flashes are usually a major concern and various methods are used to prevent and quench them.
Switchgear Classification by Location
Based on location, switchgear can be classified as outdoor, indoor, or underground switchgear. Outdoor switchgear is mostly found in substations and power plants or along power distribution lines, while indoor switchgear is normally used in residential, commercial, and industrial buildings.
Because of its location, outdoor switchgear is usually designed to withstand the harsh environment of these applications such as dust, and rain, and other elements. Most outdoor electrical switchgear is air insulated, and typically has high voltage above 66Kv.
As the name suggests, indoor switchgear is installed inside buildings, usually in a switchgear room, and is, therefore, not exposed to the same harsh conditions as outdoor switchgear. It also uses a variety of options for insulation, including air, oil, and gas depending on the required level of safety and other factors.
Underground switchgear is normally housed underground and the space above it is often utilized for other purposes. Most of the time, it’s suitable for places where space is limited, such as in densely populated areas. It’s also used when it’s not practical to have above-ground switchgear, such as environmentally sensitive areas.
Switchgear Classification by Current
Electrical systems usually either carry alternating current (AC) or direct current (DC) and use differently designed switching devices. Depending on which type of current the system is carrying, the switchgear will be classified as either AC switchgear or DC switchgear.
AC switchgear is designed for systems that carry alternating current. This includes most power systems, as well as many industrial and commercial applications. AC switchgear can be further classified as either single-phase or three-phase switchgear.
DC switchgear is designed for electrical systems that carry direct current. This kind of switchgear is mostly used in transportation applications such as railway electrification, as well as some power distribution systems today that use DC.
Switchgear Classification by Insulation
Electrical switchgear can use a range of insulation methods such as air, gas, oil, or vacuum. It’s important to select the right insulation for the particular application, as each has its own advantages and disadvantages. Read more about these switchgear insulation mediums below.
Air Insulated Switchgear
Air insulated switchgear (AIS) uses air as an insulating medium. AIS is mostly used at high voltages due to the large size of the equipment required. The disadvantages of air insulated switchgear include its susceptibility to environmental conditions such as dust, humidity, and temperature
Gas Insulated Switchgear
Gas insulated switchgear (GIS) uses a gas, such as sulfur hexafluoride, SF6, as an insulating medium. GIS is mostly used at high voltages, as it offers a compact solution for these applications. Gas also offers a high dielectric strength and lower maintenance needs.
Oil Insulated Switchgear
In some types of switchgear, oil is used as insulator. Oil insulated switchgear (OIS) offers several advantages such as high arc quenching capability and providing insulation to exposed contacts. However, oil s flammable. During the arc quenching process, the oil also produces carbon particles that reduce its dielectric properties over time.
Vacuum Insulated Switchgear
In a vacuum, there are no molecules to conduct electricity, making it an ideal insulation for switchgear. Vacuum insulated switchgear uses a vacuum as an insulating medium, and is mostly employed in high voltages systems. In addition to offering excellent insulation, vacuum switchgear provides quiet operation, fire-free insulation, and compact construction.
Switchgear Classification by Design
Another way to classify switchgear is by design, which includes both the construction and the operation of the switchgear. It may be removable switchgear that’s housed in removable cabinets or non-drawout. The design can also be a metal enclosed, metal clad or pad mounted structure.
Metal Enclosed Switchgear
Metal enclosed switchgear is a type of switchgear that uses a metal enclosure to protect the electrical components from the environment. This gear is mostly used in industrial applications. With metal enclosed switchgear, grounding is necessary to ensure safety.
Metal Clad Switchgear
Metal clad switchgear is similar to metal enclosed switchgear, but uses additional metal covers for the individual compartments or switchgear components. This gives rise to a compartmentalized switchgear structure. The compartments are also often insulated grounded individually – and removable.
Pad Mounted Switchgear
Pad mounted switchgear refers to a type of switchgear that is mounted on a pad or platform which can be made of concrete or fiberglass. This gear is mostly used in utility applications, such as power distribution and underground substations.
You may also be interested in knowing what smart (or intelligent) switchgear has to offer when compared to the standard or traditional type. But first, what is smart switchgear? Smart switchgear is used to refer to the type of modern switchgear that also includes computerized control.
The intelligent switchgear not only has the basic functions of traditional switchgear, but also has many new functions such as remote monitoring, protection, communication, and control.
The intelligent control unit’s the core of the entire system: it collects information in the distribution network using various technologies, completing real-time monitoring and allowing switchgear automation
The application of smart switchgear can effectively improve the reliability and stability of power supply, improve the economic benefits of enterprises, and provide an important technical guarantee for the safe and stable operation of the power network.
Electrical switchgear plays a vital role in ensuring the safety of people and equipment in an electrical system. By disconnecting or isolating circuits and equipment, the apparatus prevents injuries and damage in case of an electrical fault or during maintenance sessions. As we have seen, switchgear covers a wide range of electrical equipment from circuit breakers and isolators to fuses and switches. It also ranges widely in terms of voltage rating, from low to high.