In an electricity network, circuits are underground cables and overhead lines, which connect substations, generators and customers together.
Every circuit is given a power rating, to prevent them from getting too hot. These ratings are sometimes referred to as thermal ratings, due to the relationship between the current that is flowing and their temperature. Typical ratings are as follows:
• 11kV circuits – 1MVA up to about 10MVA
• 33kV circuits – 15MVA up to about 50MVA
• 66kV circuits – 30MVA up to about 100MVA
• 132kV circuits – 50MVA up to about 250MVA
Connections of new generators or demands can cause the rating of the circuits to be exceeded. When this happens, the network company will need to undertake reinforcement of the network before the new scheme can be connected.
This has a significant impact on developers looking to connect new demand, generation or energy storage projects, to either increase costs or lengthen timescales to connect, or both.