Circuit losses

Electricity is distributed around our network via underground cables and overhead conductors. Generally, the conductor size is determined by the power required and number of customers supplied, for example, a cable supplying a single house will be small, whereas one supplying an entire town will be large. Conductors are made of either copper or aluminium and the larger the conductor, the lower its resistance will be.

When current passes through an electrical resistance, it creates heat. This is similar to mechanical friction, where two objects rubbing together create heat. As more current flows, more heat is created, but this isn’t linear: One unit of current flowing may create one unit of heat, but two units of current would create four ‘units’ of heat, a quadratic relationship. Smaller conductors have a higher resistance which makes it harder for current to pass through the conductor creating more heat.

In summary the total heat and therefore the energy losses generated is a product of the current passing through a conductor and the conductor’s resistance.

A larger conductor is more expensive than a smaller one so, historically, to keep costs to customers as low as possible, conductor size was always selected relative to its application. But the cost and disruption of digging up a footpath or road to install a cable is significant. Where it is economically justified, we will always install the largest conductor, and we have changed our design standards to reflect this.

We can also control network losses by managing the current that passes through conductors. We have a few options available to us to do this and we investigate these elsewhere in our losses strategy.