Measurement of Self Cooled Transformer Sound Levels in Relatively High Ambients

Measurement of the sound level of a self-cooled transformer can be made at high ambient levels provided the ambient contains little or no sound from other inductive apparatus at the transformer sound frequencies. By measuring the components of transformer noise through narrow pass-band filters that largely exclude broad-band ambient noise and making a true RMS summation of components mathematically, it is shown that useful measurements can be conducted in ambients as high as eight decibels above the transformer sound level. A beneficial by-product is the detailed description of the frequency composition of transformer noise made available to the designer and user.