Applications of Step-up and Step-down Transformers

This is part of the HSC Physics course under the topic Electromagnetic Induction.

HSC Physics Syllabus

  • analyse applications of step-up and step-down transformers, including but not limited to:

- the distribution of energy using high-voltage transmission lines

Applications of Step-up & Step-down Transformers

This video analyses the applications of step-up and step-down transformers. Specifically, it explores how they play into the distribution of energy in high-voltage transmission lines.


Step-up & Step-down Transformers in Transmission Lines

step-up transformer is one that increases the voltage going from primary to secondary coil. As such, it has more primary windings than secondary windings. Conversely, a step-down transformer decreases the voltage, having fewer secondary windings than primary windings.


As electricity travels along a transmission line, there will be power loss due to resistive heating. The amount of power lost depends on the magnitude of current and the resistance of the wires.


$$P_{loss} = I^2 R$$


Recall that in a transformer, the voltage is inversely proportional to current.




As such, by using a step-up transformer to increase the voltage, the current flowing along the transmission line will decrease. This will significantly decrease the power loss, which is proportional to the square of current.


However, this is only useful when electricity travels through the many kilometres of countryside to get from power station to households. When the electricity enters residential areas, it is incredibly dangerous to keep this high voltage. Such a high voltage is also incompatible with domestic appliances (household voltage in Australia is 240 V). This is why a step-down transformer is used near residential areas to decrease the voltage back down.


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