The effects of flexible bonding of laminations in a transformer core

Abstract

Arising from fundamental work, various authors [1, 2] have suggested that the harmonics in a transformer noise spectrum (mainly responsible for the total noise) could be reduced by using either material of improved stress sensitivity or modified forms of transformer construction. The magnetostrictive vibrations of stacks of small silicon iron laminations can be reduced considerably by bonding the laminations together with a flexible adhesive and so the possibility of producing improved transformers has been explored. A direct comparison of the properties of a 20 kVA core built in two ways has been made. A core was constructed, first by bolting and then by bonding, and the noise, vibration and power losses of both cores were measured at various flux densities. Although the actual core vibration was reduced by a factor between five and ten, particularly the higher harmonics, and the vibration envelope was more uniform in the bonded case, the noise output of the core was only 3 dB lower after bonding. A core loss reduction of up to 4% was obtained below 1·6 T after bonding, but above this the power loss was higher in the bonded core. A possible interpretation of these results is discussed.