Empirical Transformer Noise Prediction

**Strutt|Input Data|Empirical|Transformer** inserts sound power levels into the active row of the worksheet.

The sound power level of transformers can be calculated using formulae from Bies and Hansen or IEC 551:1987.

**Bies and Hansen** calculate the total sound power level using the equation:

`L_W = N_R + 10log_10 S + C`, (dB re 10^{-12} W)

Where,

`N_R` is the NEMA sound level rating, which is the average sound pressure level measured around the transformer at a distance of 0.35 m. Values of N_{R} based on transformer power (KVA) and transformer type are sourced from Table 11.28 Bies and Hansen.

`S` is the surface area (m^{2}) of the four transformer walls (excluding the top).

`C` is the correction term, values are as listed in Table 11.27 Bies and Hansen. The value of C depends on the installation location.

Octave band sound power levels are then calculated by subtracting the values in Table 11.26 Bies and Hansen.

**IEC 551:1987** calculates the overall A-weighted sound power level by:

`L_(WA) = 74 + 14log_10(MVA)`, where MVA is larger than 0.2;

`L_(WA) = 64`, where MVA is less than 0.2

The installation location and octave band sound power level are calculated as for Bies and Hansen.

**IEC 60076-10:2001** calculates the overall A-weighted Standard Maximum sound power level by:

`L_(WA) = 66 + 14log_10(MVA)`, where MVA is larger than 0.2;

`L_(WA) = 56`, where MVA is less than or equal to 0.2

The Reduced Maximum sound power level is calculated by:

`L_(WA) = 58 + 14log_10(MVA)`, where MVA is larger than 0.75;

`L_(WA) = 56`, where MVA is less than or equal to 0.75

The installation location and octave band sound power level are calculated as for Bies and Hansen.

References:

- Bies, D., Hansen, C., Engineering Noise Control pp554-556
- AS2374.6 (IEC 551:1987) pp22-23
- AS 60076.10:2009 Annex ZA4 / IEC 60076-10:2001

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