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Electric Substations: Types and Functions

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As we told you on an earlier post, electric substations are a vital element in the electricity grid. This time, we would like to make it very clear that a substation is not merely an interconnecting element for power lines as there are different types. Therefore we are going to look little more closely at them to see the typology that exists and what they are for.

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Power lines and electric substations are primarily used to transport electricity.  However, such transport is not the sole purpose in the particular case of a substation.

The power flow in an electricity grid normally goes from the power generating stations to the load points, passing through lines and substations along the way. It is important to highlight that as the energy is transported, its conditions vary given that they differ to what is consumed (normal household consumption is 220 V) and what is generated (a generator can step up the power produced to 6.6 kV).  Additionally, conditions with which power is transported and distributed also vary, ranging from 400 or 220 kV medium voltage distribution networks with 33 kV or low voltage 220 V.

Therefore, we can find different electric subsytstems that operate at different voltage levels. These subsystems are also exploited in various ways as they can either be meshed or radial networks.

” Among the main tasks of a substation we highlight the interconnection of different circuits, electric system configuration and even insulating parts affected by an electrical fault.

The main functions of a substation can also be commented on:

  • Interconnection: Interconnecting different circuits of varying voltages or different lines at the same voltage.
  • Operation: Configuring the electric system in order to direct the power flow in an optimal manner.
  • Safety: Insulating those affected parts of the system after an electric fault, thereby ensuring both the electrical safety and supply.

It must be pointed out that all substations perform these tasks. Nevertheless, tasks aside, substations may vary in terms of the sizing of power equipment and their physical makeup, in the size of the plot of land, insulation distances, availability in the area, etc.

” A variety of substations can be classified depending on their functions, voltage, location and even their insulation.

  • Differences can be defined by the following features, as the functionality of a substation can be:
    • Generation: Serving to connect a generator to the grid. Their sizing is for a high output at lower voltages which they transport and make available from an elevated transformer.
    • Interconnection: Circuits are interconnected at the same voltage, and therefore no power transformer is required.
    • Transforming: Interconnecting circuits at a different voltage that therefore means a power transformer is required.
    • Compensating: When it serves to compensate reactive power it has equipment such as capacitor batteries, ballasts and electronic power systems.
    • Traction: Supplying railway overhead lines, depending on whether it is a three-phase system or a two-phase and even goes from an alternating current to a continuous current.
  • Depending on the voltage,substations can be for:
    • Transporting (levels > =132 kV): Much more sizeable substations that generally administer meshed circuit configurations.
    • Distributing (
    •  The need for conditioning the equipment as well as its features will depend on the substation’s location:
    • Exterior or outdoors: Where main equipment is exposed to environmental and weather conditions.
    • Interior: The main equipment is located inside a building.
    • Off-shore: The main equipment is exposed to marine conditions on top of a platform that is anchored to the ocean floor.
  • Type of insulation:
    • Air: The means of insulation used, which are normally referred to as conventional substations.
    • Gas SF6: This way of insulating is superior to that of air and it is where all the main equipment is fed into a metal casing. The insulation distances are significantly reduced and these are normally referred to as GIS substations.
    • Hybrid: Where only each circuit’s connection equipment is fed into the metal casing.
Javier González Cubero, Engineer of Tenders. Substation Department, Abengoa Inabensa.

Javier González Cubero, Engineer of Tenders. Substation Department, Abengoa Inabensa.

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