A spokesperson for Sheringham Shoal said the planned work must be carried out to comply with the requirements of the National Grid and involves the installation of two harmonic filters at the substation, which are needed to “clean” the waveform produced by the wind farm. However, this work is not connected with the issue of the “hum” that affects some residents in Cawston and surrounding areas.
 
Some elements of the grid disturb the waveform, for example by rippling it with waveforms of a higher frequency, and these are referred to as harmonics. These harmonics at best compromise the efficiency, at worst the functionality, of the electrical appliances and machinery. A harmonic filter is designed to filter out the harmonics and re-establish the original waveform.
 
The work will be carried out by the contractor Alstom, which will be responsible for the engineering, procurement, construction, installation and commissioning the plant. The company was selected on the basis of its experience and reputation in similar project.
 
“Two harmonic filters will be fitted at Salle, one for each export cable,” explained Bjørn Mo Ostgren, general manager of the Sheringham Shoal Offshore Wind Farm. “Each filter consists of a combination of resistors, capacitors and reactors, and will be housed in a compound to the southeast side of the substation. Site access will begin during the first week of February 2015, and we hope the site will be demobilised by the end of November 2015.”
 
Although the Sheringham Shoal Wind Farm is owned by two Norwegian companies – Statoil and Statkraft – and the UK’s Green Investment Bank, it has to comply with Office of Gas and Electricity Markets (Ofgem) regulations for electricity generated in the UK’s territorial waters.
 
This means Sheringham Shoal’s transmission assets, which include Salle substation, and on completion the harmonic filters, are independently owned by an investment company, Blue Transmission Sheringham Shoal.
 
Mr Ostgren continued: “We extend a warm welcome to everyone to drop in to the exhibition on 21 January to give us the chance to explain the reasons behind this very necessary operation and to reassure them that we will make every effort to minimise the effects of the installation work on local residents.”
 
However, a group of Cawston residents, who have been campaigning against the persistent “hum” from the substation, are urging the community to attend the exhibition and ask the company what it proposes to do about the current level of noise.
 
According to James Livingstone, Steve Mumby, Alec Fisher and Paul Sutton, the installation of two harmonic filters is designed to improve power quality, not reduce noise levels, which will still exist unless the company addresses those problems separately. “This new work will not in any way reduce the current level of noise that we are currently experiencing,” the group stated.
 
“Since the December edition of Reepham Life and our last information post to concerned parishioners, we have received a further update from Statkraft on the study it will be carrying out to find the best way of mitigating the noise problems from the electricity substation at Salle Beck.
 
“On a positive note, the company has taken on board our comments regarding the specification for the work needed to be done to investigate the best solutions to the problem, which will be evaluated and included in the specification.
 
“Statkraft also states it is evaluating contractors for the third-party noise mitigation study with a target of getting the contractor selected by the end of January 2015. Its specification includes reference to two studies it has already done on the noise. Surprisingly, the company has been unwilling to share these with us, but after repeated requests, it says it is considering publishing them on its website (www.scira.co.uk).
 
“We have suggested to the company that it might consider addressing the noise problem while it has contractors on site. We also think Statkraft should be asked if this ‘new work’ will have more adverse environmental impacts on our countryside, and whether when they are on site doing this work it will take the opportunity to carry out remedial work to reduce the hum that impacts so badly on some members of the community and in some places.”
 
The group suggests that if residents cannot make it to the meeting, they should ask questions by email: info@scira.co.uk