Substations are critical components of electrical power systems, categorized into various types based on their function, voltage level, installation environment, and mobility.
The main functional types include transmission, distribution, converter, collector, step-up, and step-down substations. Voltage levels range from extra high to low, while installation environments can be indoor, outdoor, or underground. Substations may also be stationary or mobile, depending on their intended use and flexibility requirements.

Main Types of Substations by Function
Transmission Substation
Transmission substationsplay a crucial role in the electrical grid by facilitating the transfer of high-voltage electricity over long distances. These substations typically handle voltages ranging from 69 kV to 765 kV, depending on the specific requirements of the power system. The primaryfunction of a transmission substationis to interconnect various transmission lines and manage the flow of electricity between different parts of the grid.
Key components of a transmission substation includepower transformers, circuit breakers, disconnect switches, and busbars. These elements work together to ensure efficient electricity transmission while maintaining system stability and reliability. Transmission substations often incorporate sophisticated control and protection systems to monitor and manage the flow of power through the electrical network.
Distribution Substation
Distribution substations serve as the link between the high-voltage transmission network and the lower-voltage distribution network that supplies electricity to end-users. These substations typically receive power at sub-transmission voltages (e.g., 69 kV or 138 kV) and step it down to medium voltage levels (e.g., 4 kV to 34.5 kV) for local distribution.
The maincomponents of distribution substationsinclude step-down transformers, circuit breakers, and distribution equipment. These substations play a vital role in ensuring a reliable and stable power supply to residential, commercial, and industrial customers. Distribution substations are often equipped with voltage regulators and capacitor banks to maintain proper voltage levels and improve power factor correction.
Converter Substations
Converter substations are specialized facilities designed to convert alternating current (AC) to direct current (DC) or vice versa. Converter substations utilize advanced power electronic devices, such as thyristors or voltage-source converters, to perform the AC-DC conversion process efficiently.
One common application of converter substations is in long-distance submarine power transmission, where HVDC technology offers advantages in terms of reduced power losses and improved system stability. Additionally, converter substations are used in connecting offshore wind farms to onshore power grids, facilitating the integration of renewable energy sources into the electrical network.
Collector Substations
Collector substations are primarily associated with renewable energy generation projects, such as wind farms or solar power plants. These substations gather the electricity produced by multiple generators or solar arrays and consolidate it for transmission to the main power grid. Collector substations typically step up the voltage from the generation level (e.g., 690 V for wind turbines) to a higher transmission voltage (e.g., 138 kV or 230 kV).
The design of collector substations often incorporates features to accommodate the variable nature of renewable energy sources. This may include advanced control systems, energy storage solutions, and reactive power compensation devices to ensure grid stability and power quality.
Step-Up Substation
Step-up substations are essential components in power generation systems, particularly for large-scale power plants such as hydroelectric, thermal, or nuclear facilities. These substations increase the voltage of the electricity produced by generators to levels suitable for long-distance transmission. Step-up substations typically raise voltages from generator levels (e.g., 13.8 kV or 24 kV) to extra-high voltage (EHV) levels (e.g., 345 kV, 500 kV, or higher).
The primary equipment in step-up substations includes large power transformers, circuit breakers, and associated switchgear. These substations also incorporate various protective devices and control systems to ensure safe and efficient operation of the power plant and its connection to the transmission network.
Step-Down Substation
Step-down substations perform the opposite function of step-up substations, reducing high transmission voltages to lower levels suitable for local distribution or industrial use. These substations are typically located near load centers, such as cities, towns, or industrial complexes. Step-down substations may reduce voltages in multiple stages, from transmission levels (e.g., 345 kV or 500 kV) to sub-transmission levels (e.g., 69 kV or 138 kV), and then further down to distribution voltages (e.g., 13.8 kV or 34.5 kV).
Key components of step-down substations includestep-down transformers, circuit breakers, and distribution equipment. These substations often incorporate features such as voltage regulators, capacitor banks, and protective relays to ensure reliable and stable power delivery to end-users. Step-down substations play a critical role in the final stages of electricity distribution, bridging the gap between the high-voltage transmission network and the lower-voltage distribution systems that serve individual customers.

By Voltage Level
Extra High Voltage (EHV)
Extra High Voltage (EHV) substations are critical components of the electrical grid, designed to handle voltages typically above 345 kV. These types of substations efficiently transfer large amounts of electricity across vast distances with minimal energy loss. EHV substations are equipped with specialized high-voltage equipment, including massive power transformers, circuit breakers, and disconnect switches capable of managing extreme voltage levels.
Key features of EHV substations include:
- Voltage range: Usually 345 kV to 765 kV (AC) or up to 1,100 kV (DC)
- Primary function: Long-distance power transmission
- Equipment: Large-scale transformers, high-capacity circuit breakers, and advanced protective devices
- Typical applications: Interconnecting major power plants to the transmission network
High Voltage (HV)
High Voltage (HV) substations operate at voltage levels between 100 kV and 345 kV. These substations serve as important nodes in the electrical transmission network, facilitating the transfer of power from transmission to sub-transmission voltage levels. HV substations are commonly found near load centers.
Characteristics of HV substations include:
- Voltage range: Typically 100 kV to 345 kV
- Primary functions: Power transmission and sub-transmission
- Equipment: Power transformers, current transformers, circuit breakers, and busbar designs
- Applications: Connecting transmission lines to distribution networks, supplying power to large industrial plants
Medium Voltage (MV)
Medium Voltage (MV) substations operate at voltage levels between 1 kV and 100 kV. These substations are essential components of the distribution network, serving as intermediaries between high voltage transmission and low voltage distribution systems. MV substations are often found in urban areas, industrial complexes, and commercial zones.
Key aspects of MV substations include:
- Voltage range: Generally 1 kV to 100 kV
- Primary functions: Power distribution and voltage step-down
- Equipment:Distribution transformers, switchgear, and protective devices
- Applications: Supplying power to residential areas, small to medium-sized industries, and commercial establishments
Low Voltage (LV)
Low Voltage (LV) substations operate at voltage levels below 1 kV, typically 120V to 480V in most countries. These substations are the final step in the power distribution chain, delivering electricity directly to end-users. LV substations are commonly found in residential neighborhoods, small commercial areas, and light industrial zones.
Characteristics of LV substations include:
- Voltage range: Usually below 1 kV (typically 120V to 480V)
- Primary functions: Final voltage step-down and power distribution to end-users
- Equipment:Distribution transformers, low-voltage switchgear, and metering devices
- Applications: Supplying power to homes, small businesses, and light industrial facilities

By Installation Environment
Indoor Substations
Indoor substations are a type of substation designed to be housed within a building or enclosure, protecting electrical equipment from external environmental factors. These substations are commonly used in urban areas, industrial plants, and locations where space is limited or weather conditions are severe.
Indoor substations typically contain various electrical equipment, including power transformers, circuit breakers, and control systems. The layout of an indoor substation is carefully designed to optimize space utilization and ensure proper ventilation and cooling of equipment.
Outdoor Substations
Outdoor substations are the most common type of substation, designed to operate in open-air environments. These substations are typically found in rural areas, industrial zones, and locations where space is not a constraint.
Outdoor substations must be designed to withstand various environmental challenges, such as extreme temperatures, humidity, and potential natural disasters. They often incorporate protective measures like lightning arresters and grounding systems to ensure safe and reliable operation.
Underground Substations
Underground substations are an alternative to surface substations, particularly useful in densely populated urban areas where land is scarce and expensive. While they can be more expensive to build than surface substations, underground substations offer long-term benefits in terms of land use efficiency and environmental impact.

By Mobility
Stationary (Permanent) Substations
Stationary or permanent substations are the most common type of substation in the electrical grid. These substations are fixed installations designed to operate for extended periods at a specific location.
Mobile Substations
Mobile substations, also known as portable substations, are designed to provide temporary or emergency power supply solutions. These substations are built on trailers or skids, allowing for easy transportation and rapid deployment to various locations as needed.
The primary purpose of mobile substations is to maintain electrical service during planned outages, emergency situations, or natural disasters. They can also be used to supplement existing infrastructure during periods of high demand or to provide temporary power for construction sites and special events.