Sub-Station Acoustic Monitoring & Modelling

About the project

Enable Design (formerly known as Equate Design) were commissioned to measure existing background noise levels surrounding a new sub-station in Tunbridge Wells, as well as noise levels generated by the substation installation, following complaints received by the client, Network Rail, from local stakeholders.

The challenge

The substation is in operation 24 hours a day and is understood to increase noise emissions when trains are about to pass by. The location consists of a weather enclosure, which is 5 m in height and houses the power transformer. It was observed on site that the roof and wall panels of the enclosure are separated by approximately 0.3 m gap around the perimeter, which was assumed to provide ventilation to the transformer. The transformer was approximately 32 m away from the rear boundaries of the closest residents, and there is an existing 3 m-high solid barrier fence located approximately 2 m away from the transformer.

We were required to assess any impact from the installation of the new sub-station in terms of acoustic detrimental effects on local residents and conformance with permitted development noise level requirements, and to undertake modelling of any mitigation measures that could be implemented if required (e.g. acoustic barrier).

The solution

Measurements were undertaken at six monitoring positions, with the choice based on accessibility and on collecting representative noise data in relation to the site.  These receptor positions were at various points, including representative locations at the houses of local residents, on both ground and upper storey levels.

The measurement procedure complied with BS 7445: 1991: ‘Description and measurement of environmental noise, Part 2- Acquisition of data pertinent to land use’.

Attended noise measurements were undertaken to the rear of the residents’ gardens during the day and night, whilst the automated, unattended survey measurements were running automated throughout the period. All measurements were undertaken on a tripod approximately 1.5 m above ground level and in free-field conditions, therefore no reflection correction was applied. The measurement duration for near the residential properties was a minimum 10 minutes. All measurements were undertaken in November 2019.

Measured noise levels were used to determine noise emissions criteria and noise emissions from the substation. The report presented the results of the environmental surveys, followed by acoustic noise modelling of a proposed acoustic screen, noise impact calculations and a discussion narrative.

The Team

• Project Manager
• Survey Engineers
• Acoustic Engineers

The deliverables

• On-site surveying of noise levels, both attended and unattended
• Acoustic survey report to NR and British Standard requirements
• Proposals for mitigating measures to reduce impact
• Feasibility report on construction of mitigating measures