How Does an Electrical Substation Work?

How Does an Electrical Substation Work?
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What is a Substation?

How does an electrical substation work? Why is it known as a “substation?” Normally stations are where we catch trains or buses. By the same analogy we can explain what a substation does. Electricity has to be transmitted over large distances as the place where the power is being generated and the place where it is consumed can be far apart. The electricity is transmitted at very high voltages and low currents to reduce the heat, eddy currents, and other transmission losses. The substations are where the voltages are increased to high values by using step up transformers, and after the transmission, they are again stepped down for distribution. In addition to changing the voltages the substations have, a variety of protective devices like circuit breakers and fuses are present to protect the distribution networks. These are designed in such a way that various distribution circuits can be isolated for repairs and load shedding. Substations are normally outdoors and are enclosed by a wire fence. However in residential or high density areas, the substation may be indoors and housed inside a building to restrict the humming noise of the huge transformers.

View of a Substation

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Function of Substations

While electric substations take part of the distribution of electricity, they have many other functions as follows:

    1. Step up and step down of the voltage for transmission and distribution. As power is transmitted at a higher voltage over long distances, the current is lower. This results in lower transmission losses but doesn’t provide the proper current for homes and businesses to use - thus the need of stepping up and stepping down the voltage.
    2. Switching and isolating the circuits for maintenance: Switching is also an important function of substations. Closing down a feeder circuit when the load demands are high needs to be done for the safety of the generating plants. Switching high voltages is dangerous work, and special circuit breakers like air circuit breakers and oil circuit breakers for reducing arcs have to be used.
    3. Load shedding: When the power demand is more than the supply, the substations do load shedding on distribution circuits to maintain balance across the electrical network.
    4. Correction of power factors circuits: The power factor has to be kept at the correct value when reactive loads are there to protect the generating plant and increase efficiency. Read this link for more information on how power factor correction saves power.
    5. Safety devices like circuit breakers and fuses: These safety devices are provided for protecting the machinery on the distribution circuit as well as in the substation against high short circuit currents.
    6. It contains bus bars for splitting the power for distribution: Thick bars of copper to which various distributing circuits are connected by nuts and bolts are known as bus bars.

Power Distribution

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Operation of a Substation

Electricity is generated in a thermal power plant, hydroelectric power plant, and nuclear power plant, etc. This electricity is then supplied to a transmission substation near the generating plant. In the transmission substation the voltage is increased substantially using step up transformers. The voltage is increased to reduce the transmission losses over long distances. This electricity then is supplied to a power substation where it is stepped down using step down transformers and then supplied to a distribution grid. In the distribution grid there are additional transformers and voltage is further reduced for distributing further down the grid. From here the electricity is supplied to step down transformers near residential quarters that step down the voltage to 110/220 Volts as per each country’s requirement.

Image Credit

    1. Substation:
    2. Power Distribution: