We give more detail of the fields from different types of substations. In each case click on the link for more details of the field it produces.
National Grid substations
Sealing End Compounds
A sealing end compound is where an overhead line joins on to an underground cable. It looks a bit like a small substation, surrounded by a metal fence, but does not contain any transformers or switchgear.
These are like National Grid substations but smaller and transform electricity between 132 kV, 33 kV and 11 kV. They produce fields in a similar way to a National Grid substation, only generally at a lower level reflecting the lower voltages and smaller sizes.
Final distribution substations
These transform the electricity from (usually) 11 kV to the voltage used in the home, 230 V. See more details of the magnetic field they produce. They come in different types:
Indoor - built into a small building which may look like a garage, or as part of a bigger building. The clue is the safety sign on the door. This is the one type of substation which can sometimes give markedly raised magnetic fields beyond its own confines.
Numbers of substations in the UK
The following table gives numbers of substations in the UK published in 2011:
Typical Voltage Transformation Levels
Approximate number nationally
Typical Number of Customers Supplied
|Grid||Grid Supply Point||400kV to 132kV||380||250m by 250m||200,000/500,000|
|Bulk Supply Point||132kV to 33kV||1,000||75m by 75m||50,000/125,000|
|Primary||33kV to 11kV||4,800||25m by 25m||5,000/30,000|
|Distribution||11kV to 400/230V||230,000||4m by 5m||1/500|
In addition there were 349,000 pole-mounted 11 kV/400 V transformers.
source: ENA Adaptation to Climate Change First Round Report under the ARP, Electricity Transmission and Distribution Network Companies, 23 April 2011