Phase unbalance

We use three-phase alternating current (AC) systems to distribute electricity. The reasons behind this are fairly technical but it means that each circuit has three live conductors and a neutral so that we can distribute more power than we would otherwise be able to.

Three-phase systems operate most efficiently when the phases are balanced. This means that each phase has the same voltage and current as the others. In reality, as each phase supplies many customers, all with differing equipment connected, the voltage and current will be different at any given time.

Losses increase when supplies aren’t shared equally across three phase network. This is because the current in one phase is higher than in the other two and this leads to extra losses with current will flow in the neutral conductor.

To create a balanced system it’s necessary to spread supplies evenly across the three phases. This may mean connecting an equal number of customers to each phase. But, as each customer will use different amounts of power at different times it’s not always straightforward.

By measuring the current flowing through each phase of a circuit we can identify where phase unbalance exists. Measurement can be expensive and time consuming and often it’s better if we’re able to model network behaviour based on data that’s available to us. We expect that smart meters will help to provide visibility of what’s happening on the network and we’re working on ways to use this data where available.

We may then decide to connect customers to different phases if we think that the improvement in losses will outweigh the cost of reconnecting the customer’s supply.