Types of Switchgear and Their Functions in the Electrical Industry

Switchgear protects electrical equipment, ensures safe power distribution, and detects broken connections. Different types of switchgear are suitable for different tasks.

1. based on voltage levels

Here are three main categories based on voltage levels, each with their benefits.

Low Voltage (LV) Switching Equipment:

Low-voltage electrical equipment controls electricity up to 1 kV, designed to generate, transmit, distribute, and consume power up to 1000 volts and 6000 A current.

This distribution equipment consists of three levels of power transmission: intake, sub-supplier, and feeder, with a sealed metal structure. The device is capable of withstanding up to 30 fault cycles without tripping.

Application: This equipment is often installed on the secondary side of power distribution transformers, and is suitable for businesses and residences such as schools, hospitals,

offices, and homes.

Medium Voltage (MV) Switching Equipment:

This equipment is used to supply electrical energy connected with multiple power systems, and can be used on circuits up to 36 kV voltage.

Medium voltage switches have the main purpose of stopping unwanted power flow.

Application: MV distribution equipment is used at primary and secondary power levels, such as in buildings, industrial, commercial, and utility installations such as generators, motors, feeder circuits, and transmission and distribution lines.

MV switches are also used in heavy power distribution, including in hydro and solar power plants.

High Voltage (HV) Switch Equipment

The transfer of electrical energy from a power plant to a neighboring city or country is called “power transmission”. 

High-voltage switch equipment is used for systems with voltages of 36 kV or more, as they require switching and protection.

HV switch equipment is designed with high safety features due to the larger voltage, which is prone to sparks during operation. 

These switches are generally used to break the main power supply circuit and feature isolators and reclosers for automatic recovery, which cut off the faulty part and close the healthy part after detecting a fault.

Applications: HV switches are used in power plants, distribution networks and other utility systems for supervision, circuit separation during faults and other functions.

2. Based on Insulating Media

The insulating medium in electrical equipment is the medium inside the enclosure that protects the live parts from accidental arc faults. The following are various types of switchgear based on the insulators used to cover electrical equipment.

Air Insulated Switching Equipment (AIS)

Air-insulated electrical equipment uses air as an insulator between the conductor and ground, with two circuit breaking principles: blowing technique or arc magnetic force.

AIS is suitable for voltages of 11 kV to 36 kV and settings at high altitudes, as the pressure remains stable. Its advantages are simple design and lower cost compared to gas-insulated switches.

However, air has a low dielectric strength and is less effective as an insulator. Also, these devices are bulkier and susceptible to moisture and temperature extremes.

Oil Circuit Breakers

Oil-immersed switchgear allows safe regulation of electric arcs. It is one of the oldest circuit breakers used in distribution and substations. Oil, being a stronger dielectric insulator than air, also improves cooling capabilities.

Oil circuit breakers use oil that turns into vapor to discharge a jet of oil along the arc. The oil is then vaporized and mostly decomposes into hydrogen gas, forming a compressed gas bubble around the arc, preventing re-strikes after the current passes through zero.

Sulfur Hexafluoride (SF6) Circuit Breaker

Sulfur hexafluoride is used as an insulating medium in GIS to extinguish arcs in HV to 800 kV circuit breakers, such as in power plants and power grids. This gas has high dielectric strength, thermal and chemical stability, and is non-toxic.

With its superior insulating properties, SF6 is more efficient at extinguishing arcs than air and oil, reducing damage to circuits. However, SF6 is a greenhouse gas and is more expensive than AIS.

Gas Insulated Switching Equipment (GIS)

Pressurized gas has a higher dielectric strength than air and requires less installation space. GIS applications are suitable in locations with high land costs, limited space, corrosive air, dust, or in areas where it snows frequently.

Sulfur hexafluoride is often used as an insulating gas in switch systems, but other gases such as carbon dioxide can also be used. The choice of GIS depends on space requirements, environmental conditions, and equipment life cycle costs.

GIS switch equipment is commonly used in railroads, hydro stations, large cities with limited space, underground substations, hilly areas, and high-voltage transmission systems.

Vacuum Circuit Breakers

Vacuum switch equipment works by utilizing vacuum to eliminate electric arcs after air is evacuated from its space. Compared to other types, vacuum switches are less suitable for breaking direct current faults as there is no 'zero current' period.

With high dielectric strength, vacuum switches are very efficient in extinguishing arcs as there is no ionization. 

This makes them ideal for high voltage with more compact components. However, vacuum switches can be more expensive, especially for voltages above 38 kV.

3. By Type of Application

Depending on their use, electrical appliances can be broadly classified as follows:

Outdoor Switch Equipment

Outdoor switch equipment is installed in the open and has the ability to operate at high voltage or extra high voltage. 

Outdoor equipment is larger and has electrical enclosures made of weather-resistant materials than indoor equipment. Natural ventilation is used for the cooling system.

For high-voltage installations, a large area between the insulator and conductor is required. Circuit breakers, insulators, transformers, bus bars, and substation equipment require considerable space for electrical clearance at high voltages.

Application: Outdoor switch equipment is used at voltages above 66 kV. It is applicable for high-voltage transmission, substations, and industrial applications.

Indoor Switch Equipment

Indoor switch equipment is typically used for medium voltage (MV) and is protected by an earthed metal housing. These switch systems are designed to be installed in clean, dry, temperature-controlled indoor locations, with ventilation using fans or air conditioners.

Indoor electrical equipment offers safety, efficiency and lower costs than outdoor equipment, although its use is limited to lower voltages.

Applications: This equipment is installed indoors for voltages below 66 kV and is used in substations, residential areas, and commercial areas.

Conclusion

To choose the right electrical equipment for your needs, it is important to understand the different types of electrical equipment. 

This equipment is used to safely transmit electricity to residential, commercial, and industrial sectors. Different types of switchgear have specific functions, so proper placement is essential.