How a Substation Works
How does a substation work?
Substations are used for stepping up voltage for transmission, stepping it down
for distribution, and for switching purposes. In this article we discuss the
various functions of a substation and its working principles. We also discuss
the safety devices used.
Substation
How does a substation work?
Why is it known as a “substation?"
Normally stations are where we
catch trains and where people get on and off. 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
changing the voltages the substations have a variety of protective devices like
circuit breakers and fuses 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
Function of Substations
The substations apart from the
distribution of the electricity have many other functions as follows:
1. Step up and step down of the voltage for
transmission and distribution: As for the same power transmitted at a higher
voltage the current is lower it results in lower transmission losses, hence is
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 a dangerous work,
and special circuit breakers like air circuit breakers and oil circuit breakers
for quenching the 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.
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.
5. Safety devices like circuit breakers and
fuses: These safety devices are provided for protecting the machineries 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
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.