The sound-field characterisation of a power transformer

In order to effectively suppress the noise radiation from large electrical power transformers, both the structure-borne and air-borne sound fields nee d to be characterised. The characterisation can be made either from theoret ical predictions or by in-situ measurements. This paper presents the study of the sound radiation from a large power transformer in a substation. The radiation pattern can be predicted from the measured acceleration distribut ion and the predicted value is not affected by other noise sources. Alterna tively, the farfield sound pressure level can be predicted from the sound p ressure level measured at NEMA locations. Both the near- and far-field powe r radiation can be in-situ measured using the sound intensity technique. It is shown that both the vibration of a transformer tank wall and the radiat ed noise consist of a series of tonal components mainly at the first few ha rmonic frequencies of 100 Hz. Also, the neglect of the noise radiation from the transformer (top and bottom) lids does not affects the accuracy of the transformer radiation characterisation. (C) 1998 Elsevier Science Ltd. All rights reserved.