LOAD NOISE INCREASE OF TRANSFORMERS BY LOAD HARMONICS

Abstract

Harmonic components in the load-current have a larger impact to the increase of the load noise level of transformers than might be expected from their amplitude. The reasons are (a) the interaction of the harmonics with the large load-current at power frequency, (b) the rising sound radiation efficiency with frequency and (c) the A-weighting filter curve which suppresses sound components at lower frequencies. This paper presents a calculation scheme able to estimate the noise increase and the noise spectrum of electrical transformers for non-sinusoidal load conditions. The proposed calculation scheme is applied to three practical examples