We in SVU have been working to try to identify the impact a sub station would have on our countryside in the area of Twinstead and Heddingham which are potential sites for this installation if corridor were chosen as the new power line route. When David Holland, a Parish Councillor for Twinstead went to the Consultation Event at Hadleigh, he felt the display which includes the image shown above, understated the impact and so requested further information as follows. We also include the response from Jim Street of National Grid along with the photograph (Top) of one of the transformers we are discussing.

Questions to National Grid:-

Please can you confirm that the transformers that would be required for the corridor two option would be larger than those shown in the supplied picture as this is railway supply GSP and is not supplying a large geographical area as would be the case with the corridor 2 option.

Also, as this is a matter of particular import to the people of Twinstead and Heddingham, please can you also tell me what measures you could take to mitigate the 100hz sound pollution that would result from the working of the transformers.

The response from National Grid:-

In response to your questions - the transformers at Patford Bridge (shown above) are 400/25kv units, the ones that would be installed at the new substation should Option 2 be taken forward are 400/132kV units. The tanks on latter units will have a slightly larger footprint, than those at Patford Bridge, approximately by 1m in both length and width. As the higher voltage for both units is 400kV, the height of both will be the same. I attach for your information a picture of a 400/132kv transformer tank being delivered to one of our other substations. We have shown a picture of Patford Bridge as this represents the best example we have of a substation that contains what is effectively only two 400kV transformers and their associated switchgear. 

In terms of noise. At the design stage we would undertake a background noise assessment at the nearest residential properties. It is our policy that any operational noise from our equipment should not increase the background noise level at these properties from that which currently exists. If necessary, the transformers can be accommodated in an acoustic housing in order to achieve this. 

Best regards

Jim Street

Senior Project Manager