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 NR based on transformer power (KVA) and transformer type are sourced from Table 11.28 Bies and Hansen.
`S` is the surface area (m2) 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: