7.3.6 Transformer Equations

Power in transformers

If the transformer is 100% efficient, the power in each coil will be the same - this means that:

potential difference across primary coil × current in primary coil = potential difference across secondary coil × current in secondary coil

$$Vp×Ip=Vs×Is$$

Electricity is generated in a power station at 25,000 V, and to transmit the electricity across the country on the National Grid, transformers increase the potential difference to 400,000 V.

This means that the transformer increases the potential difference by a factor of 16. So if there are no energy losses in the system, the current would also be reduced by a factor of 16 as:

$$power = potential difference × current$$

Reducing the current by a factor of 16 means that the heating effect of the current is reduced by a factor of 256 (16²), as:

$power = current^2 × resistance$

This means that the energy is transferred more efficiently, as less energy is dissipated as heat.