Transformers and Power Transmission

Transformers are devices that change the voltage of an alternating current supply. They are among the most important practical applications of electromagnetic induction and are essential to the efficient transmission of electrical power across the National Grid.

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How a Transformer Works

A transformer consists of two coils of wire (the primary and secondary) wound on a shared iron core.

1. An alternating current in the primary coil creates a changing magnetic field
2. The iron core channels this changing magnetic flux to the secondary coil
3. By Faraday's law, the changing flux linkage through the secondary coil induces an alternating EMF

The transformer only works with alternating current because a steady (DC) current produces a constant magnetic field — there is no change in flux and therefore no induced EMF.

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The Transformer Equation

For an ideal transformer:

Vₛ / Vₚ = Nₛ / Nₚ

where:

• Vₛ = secondary voltage
• Vₚ = primary voltage
• Nₛ = number of turns on the secondary coil
• Nₚ = number of turns on the primary coil