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Transmission Substations and Distribution Substations

What does a transmission substation do?

A transmission substation is a place of power distribution from the electric company. It is used to convert high voltage electricity from one form to another and send the energy on to the next step in the power grid. These substations can be seen as a hub or intersection, with lines coming in from all directions.

They play a critical role in the distribution of power from the power plant to consumers. Transmission substations are used to increase or decrease the voltage of electricity as it travels through the grid. This allows for a more efficient and reliable distribution of power.

Transmission substations at the power plant

When the voltage of electricity is sent from a power plant to a transmission substation, it can be increased or decreased according to how far away the substation is. Electricity will be distributed at line voltage if it travels short distances, because there will not be much loss over such a small distance.

However, when distributing power for longer distances, the voltage of the electricity must be increased. Electricity intended for long distance transmission over high voltage transmission lines can be up to 750,000 volts. Higher voltage allows for less electrical loss over long distances, meaning that there will be more electricity reaching its destination. With the correct amount of voltage, almost all of the power supplied by the power plant can reach its destination in a transmission substation.

Texas wind energy production is mostly located in West Texas.  This necessitates the transmission of electricity over long distances to reach larger population centers.

A transmission substation is mainly used to help control how much power is sent out to the consumer. The voltage of electricity can be increased or decreased at the head of the line, which allows for more precise control over how much energy ends up at each house and business.

What does a transmission substation look like

A transmission substation can come in a variety of shapes and sizes, but they all have one common goal- to distribute power from the electric company to consumers in an efficient and reliable way.

The exterior of a transmission substation can be quite imposing, with large metal towers and high voltage wires. However, the inside is quite sterile and functional, with lots of equipment used to control the flow of electricity.

Transmission Substation
A small 115 kV substation – image credit

One thing you will always see at a transmission substation are large transformers. These transformers are used to increase or decrease the voltage of electricity as it travels through the grid. Without these transformers, the power grid would not be able to function.

Transmission Substation 2
image credit

Another important piece of equipment at a transmission substation are circuit breakers. These are the devices used to shut off sections of the grid in case there is an overload or electric malfunction. This prevents damage to equipment that could cause widespread power outages.

Curiously, some substations are located underground because they are in noisy or inconvenient places, e.g., near airports or refineries.

Types of substations

There are a wide variety of substations in the power grid, and they perform different functions. One type of substation is called a corrective or regulating substation. These types of substations play a critical role in maintaining voltage levels within predetermined limits so that loads on transmission lines do not exceed capacity. If this did happen, it could cause a blackout and widespread power outages. These substations can also help prevent overloads by providing voltage support when needed.

Another type of transmission substation is a switching station, sometimes called an interconnection substation. These types of substations essentially connect the power grid to other grids such as the interstate transmission system or an electric utility company that is not a part of the power grid. By connecting multiple grids, more power is available to consumers and a greater diversity in energy sources can be used. Switching stations allow for flexibility and diversity of power distribution.

What is the difference between a transmission substation and a distribution substation?

A transmission substation is used to increase or decrease the voltage of electricity as it travels from the power plant to the consumer. A distribution substation is used to send a constant voltage to the consumer.

A transmission substation helps to maintain voltage levels within predetermined limits, which prevents overloads and blackouts. A distribution substation sends a constant voltage to the consumer, regardless of how many appliances are being used at once. This is important because it ensures that the consumer always has access to enough power, even during peak hours when demand for electricity is high.  Outputs of distribution substations are typically below 25 kV.

Where are Transmission substations located?

Transmission substations are usually located in remote areas, away from populated areas. This is because they need a lot of space to house the large transformers and other equipment, and they need to be in a location where there is plenty of open land to install the high voltage wires. Transmission substations are also often located near power plants because they need to connect to the grid.

Who builds and maintains Transmission substations?

In Texas, Transmission substations are built and maintained by the regional Transmission & Distribution Utilities such as Oncor and AEP.

Substation Projects in Texas

Substation projects are expensive undertakings.  Projects can cost millions of dollars.  Here are few projects currently underway in Texas.

Southline 128 kilovolt Substation

This $35 dollar substation project will be located near Cleveland, TX.  It is expected to be completed in 2023 and will facilitate future load growth in the area near Cleveland TX

Castle 230 kilovolt Substation

This $53 million project will be located south of Plantersville, TX. It is expected to be completed in 2024 and will facilitate future load growth in the area near Plantersville.

Millbend 230 kV Substation 

This $72 million project will be located near Porter, TX. It is expected to be completed in 2024 and will facilitate future load growth in the area near New Caney, TX near I-69.