Operational noise from the converter stations Scenario 1: Pre-installed ducts
55.
Under construction Scenario 1, it is proposed that the East Anglia THREE cable connection will feed into a separate and dedicated converter station, located alongside the pre-existing East Anglia ONE converter station. .
56.
The East Anglia THREE converter station is proposed to be of similar size, structure and configuration to that proposed for East Anglia ONE, therefore the assumptions used in both assessments are the same. Acoustic theory would dictate that the introduction of a second converter station (producing the same noise emission sources) would represent a doubling of sound energy and thus provide a 3dB increase in the predicted receptor levels. It is considered appropriate to use the converter station modelling results obtained in the East Anglia ONE ES as an accurate representation of the noise impact associated with East Anglia THREE and increase the predicted rated receptor levels by 3dB.
57.
The noise from the converter station has been predicted by modelling the noise sources using CadnaA noise modelling software. CadnaA incorporates prediction methodology within ISO 9613: 1993 Acoustics - Attenuation of sound during propagation outdoors. The CadnaA software package is a commercially available package which implements many national and international acoustic calculation standards, including those typically used within the UK.
58. A three-dimensional model of the proposed surrounding area was constructed, based on topographical data, ordnance survey mapping and indicative layout plans of the converter stations. Typical noise emission data for the items of electrical equipment and their typical locations was obtained from a potential supplier.
59.
The following points should be taken into account regarding the noise model:
All noise emitting equipment was modelled as a point source, at a height of 3m above ground. This is considered to provide a worst case conservative approach to larger, higher structures and sound sources;
All converter station equipment was assumed to be operating concurrently, including all cooling/air handling units;
The ground surrounding each converter station was assumed to be ‘soft’ (i.e. grassland), which is representative of the actual ground conditions, whereas within the converter station the ground was assumed to include hard and acoustically reflective surfaces, such as concrete;
Preliminary Environmental Information May 2014
East Anglia THREE Offshore Windfarm
Chapter 26 Noise and Vibration Page 19
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