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.


Application of Transformers in Power Transmission

Both step-up and step-down transformers are used in the distribution of electrical energy.

Use of Step-up Transformers

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.

In power plants, electricity is often generated at a lower voltage. Step-up transformers are used to increase this voltage for long-distance transmission over power lines. As electricity travels along a transmission line, there will be power loss due to resistive heating. The amount of power loss greatly increases for long distance power transmission because electrical resistance increases with length of a conductor.

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, due to conservation of energy, the secondary voltage is inversely proportional to secondary current. So, if we increase the voltage, the current decreases.




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 due to heat (as power loss is directly proportional to the square of current).

Uses of Step-down Transformers


However, step-up transformers are only useful when electricity is transmitted over the many kilometres of countryside to get from power station to households.

Before electricity can be safely used in homes and businesses, the high voltage from transmission lines must be reduced. Step-down transformers are used in distribution substations and local poles to lower the voltage to a safe, usable level.

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.

Other Applications of Step-up and Step-down Transformers

Step-up Transformers Step-down Transformers
  • X-Ray Machines: In medical equipment like X-ray machines, step-up transformers are used to increase voltage to a level sufficient to produce X-rays.

  • Microwave Ovens: These appliances use a step-up transformer to increase household voltage to a level high enough to power the magnetron, which generates microwaves.

  • Induction Furnaces: Used in industrial settings for melting metals, induction furnaces require high voltage, which is provided by step-up transformers.

  • Consumer Electronics: Many electronic devices, including chargers for laptops and smartphones, contain step-down transformers to convert the 110-240 V AC (depending on the country) from wall outlets to a lower voltage suitable for the device.

  • Doorbell Systems: In residential doorbell systems, step-down transformers are used to reduce the household voltage to a lower level that is safe for the doorbell circuit.

  • HVAC Systems: Heating, Ventilation, and Air Conditioning systems often use step-down transformers to provide a lower voltage for controlling systems and thermostats.



Previous sectionLimitations of Ideal Transformers and Improving Efficiency

Next section: Operation of Simple DC Motors