Harmonic Index----A Tool for Transformer Audio Noise Investigation

The harmonic index is the decibel difference between the noise level obtained with the flat weighting and the noise level obtained with the 40-decibel weighting. It is a qualitative measure of the harmonic content of the noise measured at a given point. The harmonic index was introduced several years ago,¹ but it has not realized the consideration which it merits. It is the purpose of this paper to demonstrate the value of the harmonic index when used in conjunction with the flat weighting measurements as a simple approach to the problem of evaluating the complex structures of the transformer.