Switchgear protects electrical equipment, facilitates the safe distribution of power, and identifies faulty connections. Various types of switchgear are suitable for different applications. Let’s explore the major types of switchgear you should know.
1. Based On Voltage Level
Here are the three main types according to voltage rating, each having its own uses and functions.
· Low Voltage Switchgear (LV)
Low-voltage electrical switchgear usually controls up to 1kV of electricity. It is designed to generate, transmit, distribute, and consume electric power at voltage levels of up to 1000 volts and a current of up to 6000 A.
Therefore, it includes:
- Low-voltage circuit breakers
- Moulded-case circuit breakers
- Earth leakage circuit breakers
- Miniature circuit breakers
- Switch units
- Offload isolators
- HRC fuses
Mostly metallic enclosed structures, this switchgear is a three-level power transmission typically comprised of incomer, sub-incomer, and feeder. It can withstand 30 cycles of fault current without tripping.
Application: As it is typically installed on the secondary side of a power distribution transformer. Besides, it is suitable for residential and business uses like schools, hospitals, offices, and houses.
· Medium Voltage Switchgear (MV)
Medium-voltage switchgear is applicable in circuits up to 36KV, thus tolerating higher levels of electrical stress than LV. This kind of switchgear is mainly used to supply electrical energy that interconnects with more than one power system.
The primary purpose of medium-voltage switchgear is to interrupt the continuous flow of power in case all the wrong situations happen.
This comprises activities such as:
- Switching on and off
- Disruptions during short-circuit conditions
- Changing capacitive and inductive currents
Application: MV switchgear may be located at both the primary and secondary power levels. This applies to its usage in industrial, commercial, and utility buildings and installations such as generators, motors, feeder circuits, transmission/distribution lines, etc.
In addition to hydro and solar power plants, MV switchgear is used in heavy power distribution industries.
· High Voltage Switchgear (HV)
Power transmission refers to the movement of electrical energy from generating stations to cities or neighboring countries. These demand high-voltage switchgear that includes switching and protection devices. So, HV switchgear is used in 36 kV systems and above.
Due to the higher voltage level here, HV switchgear is susceptible to arc flashes during switching operation and hence includes the best safety features.
Circuit breakers, the most essential component, are mostly ‘ON’ circuits that can be employed after a long period. Therefore, circuit breakers need to be reliable enough to ensure safe operation when required.
High-voltage switchgear primarily disconnects circuits from the main power supply. The equipment includes isolators and reclosers for automatic switching, which disconnect the faulty section and close the healthy section upon fault detection.
Application: HV switchgear is predominantly used in power stations, electrical distribution networks, or other utility circuits, where it is employed for system supervision, circuit separation in faults, and other uses.
2. Based On Insulation Medium
The insulating medium in switchgear refers to the medium inside the enclosure that shields the energized parts from an accidental arc fault. The following are the different types of insulators used for switchgear enclosures.
· Air Insulated Switchgear (AIS)
Air-insulated electrical switchgear uses air as the insulation material between the conductors and the ground. It employs two principles in air circuit breakers: the puff technique or arc magnetic force.
It is suitable for voltages between 11kv and 36kv and high altitude settings, as pressure remains unchanged. One of AIS’s more notable benefits is its relatively uncomplicated design, and it often costs less than gas-insulated switchgear.
However, the air has the least dielectric strength and is among the worst insulators. Moreover, air-insulated devices are larger than devices insulated by other media and sensitive to humidity and temperatures.
· Gas Insulated Switchgear (GIS)
Pressurized gas has a higher dielectric strength than air insulation and requires less installation space. This application of GIS is required where the cost of land is high, there is limited space, and there is corrosive or dusty air, as well as during snowfall.
While Sulfur Hexafluoride is widely used as an insulating gas in switchgear systems, other gases could be utilized instead.
Carbon dioxide, for example, has a low footprint and is used as an insulating medium in breakers. The choice of GIS depends on space requirements, the environment, and the equipment’s life cycle cost.
GIS switchgear is most commonly used in railways, hydro stations, big towns with limited space, underground substations, hilly regions, and high-voltage transmission systems.
· Sulfur Hexafluoride (SF6) Circuit Breakers
Sulfur hexafluoride is used as a special insulating medium in GIS to extinguish the arc. It is employed in extinguishing arcs in HV Circuit breakers up to 800 kV in electric power stations, grids, etc.
Most notable properties include high dielectric strength, thermal and chemical stability, and non-toxic.
With its excellent insulating properties, this inert gas possesses arc quenching efficiency better than air and oil, thus preventing further damage to the circuit. However, SF6 is a greenhouse gas and more costly than the AIS.
· Vacuum Circuit Breakers
Vacuum switchgear works in matter-free conditions, utilizing a vacuum to help eliminate the arc of electricity.
Once the air is evacuated from the chamber, the switchgear starts to work. Compared with the other types, vacuum switchgear is unfit to interrupt DC faults as there is no ‘zero current’ period.
The high dielectric strength makes these vacuum interrupters highly efficient in arc extinguishing since there is nothing to ionize.
This makes it ideal for higher voltage use with compact components. However, vacuum switchgear may cost more than other options, especially when the voltage exceeds 38 kV.
· Oil Circuit Breakers
The oil-immersed switchgear apparatus allows for the control and safe regulation of arc energy. These are among the oldest circuit breakers used in distribution and substation circuits. Oil is a stronger dielectric material, a better insulator than air, and may also improve cooling capabilities.
Oil circuit breakers use limited oil to turn into vapour and expel a jet of oil along the arc length. The oil is then vaporized and decomposed mostly into hydrogen gas, and then a highly compressed hydrogen gas bubble is formed around the electric arc turn. Thereby, it prevents the re-striking of the arc after the current has crossed zero in the cycle.
3. Based On the Application Type
Depending on the usage, the electrical switchgear may be roughly classified as follows:
· Outdoor Switchgear
Outdoor switchgear is substation equipment installed in an open-air environment. It can operate at high or extra-high voltage. Compared to indoor ones, outdoor switchgear may have electrical enclosuresmade from weather-resistant materials and are bulkier in size.
The cooling system in outdoor switchgear uses natural ventilation.
Moreover, it also requires a lot of room for installation because where high voltage is needed, building works practically add to the cost of installation due to the enormous space between the large size of insulators and conductors.
Circuit breakers, isolators, transformers, bus bars, and substation apparatus require massive space for electrical clearance concerning high voltage.
Application: Output switchgear is employed where the voltage is above 66 kV. It is used in high-voltage transmission, substation, and industrial applications.
· Indoor Switchgear
Indoor switchgear is used primarily for medium-voltage (MV) switchgear, which is enclosed by a metallic housing that is usually earthed.
Interior switchgear systems are intended for installation in clean, dry, and climatically controlled indoor locations. An external cooling system, such as a Fan or AC, is used for ventilation.
Indoor switchgear offers excellent safety, security, and efficiency and is relatively cheaper than outdoor switchgear. However, its economic feasibility and utilization at higher voltage are restricted.
Application: Due to its cost implications, switchgear is installed indoors for voltages below 66 kV. It is also used in substations, residential areas, and commercial areas.
Conclusion
Understanding the various categories of switchgear is essential to help you buy the right one for your electrical equipment. Switchgear is commonly used to dispense safe electricity for residential, commercial, and industrial purposes. From the above discussions, it is clear that each switchgear has its function, and it is important to place it as such.
