Case study

Dungeness A - 275kV Grid Connection Modifications

We explore a New Grid connection to allow decommissioning of the nuclear power station to proceed.


Prior to Dungeness A power station being taken offline at the end of 2006, the 275kV grid connections had to be modified to receive rather than supply power during the decommissioning work. We were asked to carry out a study into possible options and then to provide a concept design for the most cost effective solution.



We carried out the initial optioneering and were able to show that the use of a single 275kV circuit was appropriate for the new decommissioning arrangements, rather than a separate two-circuit 33kV connection to the grid system. Once the concept was agreed with the client, detailed layouts were produced to establish that sufficient space was available within the substation, and that cable routes were appropriate.

Structural calculations were carried out and drawings were produced as the new design required the fitting of three new 275kV bushings into the west wall of the switch house to connect to a new 275/11kV transformer, situated adjacent to the wall.

A protection study was then carried out to prove that an existing set of 275kV current transformers could be re-used, and to specify the relays required.

Once the concept was proven to the client’s satisfaction, key long lead time items were specified and ordered.



Our report detailed the various options, including separate 33kV and 275kV supplies and recommended the most cost effective solution. As part of this, we produced:

  • A concept design for the modified electrical system, including plant specifications for the 10MVA, 275/11kV transformer, 11kV switchgear, protection, cables and 275kV circuit modification;
  • Plant layouts and cable routes;
  • Protection study and settings for the new circuit;
  • A structural design for the modified 275kV substation.

By the use of sound engineering judgement and knowledge of the site safety case, FrazerNash was able to make a clear case for a single grid supply to the site that allowed the use of the single 275kV spare circuit. This saved the client over £5M when compared with a twin 33kV circuit supply through a Site of Special Scientific Interest.

Frazer-Nash was able to provide a complete concept design service for the electrical and structural aspects required, ensuring that the concepts addressed in the optioneering stage were included in the finalised design.


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