Scottish and Southern Electricity Networks (SSEN) has completed a £2m project to replace two transformers at its substation in Chertsey, Surrey, and says comparable work is now under way or being planned elsewhere on its network. The company set out the details on 20 November 2025 in an article by Neil Hitchcock, project director in SSEN Distribution's Large Capital Delivery division1.
The Chertsey equipment was more than 40 years old and was "beginning to approach the end of its useful life", SSEN said. The two units were swapped for new models as part of what the company describes as a rolling replacement programme across its network areas. SSEN said the substation holds two transformers to guarantee redundancy, so that if one needs repair or servicing the network can operate as normal with no adverse impact for customers1.
"Now the Chertsey project's completed, we're moving on to the next sites; projects like this one are under way, or being planned in locations across our network areas in central southern England and the north of Scotland."
SSEN did not name the next sites, give a timetable for them, or put a total figure on the programme. Those details have not been reported1.
The company described the installation process in some detail: new transformers are "skidded" into position and manoeuvred with hydraulic jacks and beams, after which fans, radiators and the conservator are reattached. The conservator keeps the correct amount of specially formulated mineral oil in the unit, which SSEN said is vital for safe and efficient operation. The two transformers are kept a safe distance apart so that a serious fault in one is less likely to affect the other, and the newly installed units at Chertsey are surrounded by trees to reduce their visual impact1.
SSEN said the new equipment provides additional headroom so that capacity is available when homes and businesses adopt low-carbon technology such as heat pumps, electric vehicle chargers and solar panels, provided any necessary network upgrades have also been completed1.
| Item | Detail |
|---|---|
| Location | Chertsey substation, Surrey, just beyond the M25 |
| Cost | £2m |
| Units replaced | Two transformers |
| Age of old equipment | More than 40 years |
| Status | Completed |
| Further work | Under way or planned in central southern England and the north of Scotland |
Why it matters for households
Transformers convert electricity from the higher voltages used for long-distance transmission to the lower voltages homes and businesses use1. A substation's condition therefore bears directly on whether supply in an area is reliable, and on how much new load the local network can absorb.
The redundancy point is the practical one for a household: with two transformers, SSEN says a single unit can be taken out for repair or servicing without affecting customers1. The headroom point is the one that touches household energy independence most closely. SSEN states that the new capacity will be available for heat pumps, EV chargers and solar panels, but attaches a condition: any necessary network upgrades must also have been completed1. That wording indicates that a replaced transformer is not by itself a guarantee that a given property can connect additional low-carbon equipment.
SSEN's network areas cover central southern England and the north of Scotland. Households elsewhere in Great Britain are served by different distribution operators, and the article does not cover their programmes1.
What happens next
SSEN says it is moving on to the next sites, with projects of this kind under way or being planned across its network areas in central southern England and the north of Scotland1. No locations, dates or costs for those projects have been published.