Measuring No - Load and Load noise of Power Transformers using the Sound Pressure and Sound Intensity Methods - Part - I: Outdoors measurements

The subject of deciding on the most appropriate method of determining the true sound power level of a power transformer has been discussed through the transformer industry for decades. It is the objective of this 2 - Part paper to identify magnitudes of the contributions to the inherent difference in power transformer noise level measurements when using the Sound Pressure method versus when using the Sound Intensity method. The paper presents results of comprehensive outdoors and indoors measurements made of the frequency spectrum and total noise of a large number of power transformers using the two measuring methods. In Part - I of the paper, results of the outdoor measurements made on the total noise produced by three power transformers in low ambient / no sound reflections locations are presented. Results of the indoors measurements made on 48 power transformers of 12 - 336 WA power ratings are presented in Part - II of the paper. Appropriate conditions for accurate indoors measurement of transformer noise when using the Sound Intensity method have been derived. Modifications to the existing IEC and IEEE Industry Standards of transformer noise testing are proposed.