levels of noise sources using sound pressure - Engineering/survey methods for use in situ in a reverberant environment.


The required modelled average SPL at 1m from the source has been calculated from the supplier quoted Lw – 10 x LOG (Surface Area of Measurement Envelope). The measurement envelope has been corrected for the radius effect at the edges of the measurement envelope 'box' and sides and top have been balanced in order that the transformer is not 'top heavy' in terms of sound power level split between the top area source and side area sources.


The averaged Lp in the model (1m from transformer box) has been compared with the calculated average Lp with appropriate amendments made to match this level.


Results inputted sound power levels to match 90 dB(A) Lw are presented in Table 2. Area Source


Octave Band (Hz) Sound Levels, dB(A)


Transformer Bank Top


Transformer Bank side


31.5 63 125 250 500 1000 2000 4000 8000 17.6 63.3 73.5 75.8 76.3 56.0 52.9 49.4 37.0


23.1 68.8 79.0 81.3 81.8 61.5 58.4 54.9 42.5 Table 2 Model Inputs for Transformer Banks


Transformer Cooling Radiator Fans (height of 4 metres) x 6 The noise level for the transformer cooling radiator bank has been inputted directly as per a supplier Lw as a point source. The input Lw to match 90 dB(A) Lw is presented in Table 3.


Point Source Octave Band (Hz) Sound Levels, dB(A)


Transformer Cooling Fan Bank 41.0 50.5 82.8 79.5 84.3 83.5 80.5 75.5 59.1


Table 3 Model Inputs for Transformer Cooling Radiator Fans


Converter Cooling Fan Bank x 20 banks of 8 fans Converter Cooling Fan Banks are represented by vertical and horizontal area sources forming a box with the Lw calculated as per the Transformer Bank above.


In addition to the calibration with calculated LP averages from 1 meter, converter cooling banks were calibrated with the SPL at 10 metres distance provided within the supplier data sheet.


The input Lw to match 90 dB(A) Lw is presented in Table 4. Area Source


Converter Cooling Fan Bank


Octave Band (Hz) Sound Levels, dB(A) Broadband


31.5 63 125 250 500 1000 2000 4000 8000 Total, dB(A) 39.1 47.1 59.1 64.1 69.1 74.1 71.1 62.1 56.1


77.2 Table 4 Model Inputs for Converter Cooling Fan Banks Broadband


31.5 63 125 250 500 1000 2000 4000 8000 Total, dB(A) 89.6


80.2 85.7


Broadband Total, dB(A)


EAOW


Noise Prediction Methodology P41388


6


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