Major TriConnex milestone at Sherford, Nr Plymouth

Triconnex has reached a major milestone on our Sherford Primary substation build with the installation on site of the first of two Power Transformers – some photos and technical details are included below.

Well done to the teams involved for the success of this project to date.

Some facts about Power Transformers
‘Power’ transformers are a larger version of the ‘Distribution’ transformers typically used within an ‘on- site’ substation with a few key differences. In addition to converting from 33KV to 11 KV rather than 11 KV to 415 KV the biggest difference is the rating. – Power Transformers are able to supply 12 MVA (that is 12,000 KVA) in normal circumstances, and have fans fitted to their external oil radiators which means that with fans running, they can run at 18 MVA indefinitely.

To change the output voltage within a range, all transforms have a device called a ‘Tap Changer’, which alters the ratio of Primary to Secondary turns in use. On Distribution transformers, this is a simple device, which can only be operated DEAD (an ‘Off load tap changer). On a Power transformer, the taps must be changed multiple times every day as when the load changes, the voltage changes too. This requires an ‘On-Load’ tap changer, which is extremely complex and expensive, a highly mechanical device that has to absorb large amounts of energy.

Only one transformer is actually required to supply the load (equivalent of about 7,000 houses). In Primaries, two are always used so that one can be taken out of service and maintained, and to provide redundancy in case of a fault on one transformer.

Each weighs 30 tonnes, and has 6,600 litres of oil for cooling and contains 3.9 tonnes of copper in the core.

Simon Gallagher TriConnex -Technical Director