Abstract
Structural vibration characteristics and vibration shapes under three-phase excitation of a archetype transformer core were investigated to consider their influences on transformer noise. Acoustic noise and vibration behavior were measured in a three-limb model transformer core. Experimental modal analysis by impact test was performed. The vibration shapes were measured by a laser scanning vibrometer at different exciting frequencies. Vibration amplitude of the core in out-of-plane direction were relatively larger than those in other two in-plane directions. It was consistent with the result that the frequency response function of the core in out-of-plane direction was larger by about 20 dB or more than those in in-plane directions. There were many vibration modes having bending deformation of limbs in out-of-plane direction. The vibration shapes of the core when excited at 50 Hz and 60 Hz were almost the same because the fundamental frequencies of the vibration were not close to the resonance frequencies. When excitation frequency was 69 Hz which was half of one of the resonance frequencies, the vibration shape changed to the one similar to the resonance vibration mode. Existence of many vibration modes in out-of-plane direction of the core was presumed to be a reason why frequency characteristics of magnetostriction and transformer noise do not coincide.
Highlights
Reducing acoustic noise is one of the important objectives in design and development of power transformers
Frequency spectrum of transformer noise or core vibration is not match with that estimated from magnetostriction of the grain oriented steel sheet
High permeability grain oriented electrical steel sheets were used for the archetype transformer core
Summary
Reducing acoustic noise is one of the important objectives in design and development of power transformers. Noise of transformer is greatly influenced by magnetostriction of the grain oriented electrical steel sheets used in the iron core. Magnetostriction properties of grain oriented electrical steel has been improved as well as reducing iron loss. Resonance of the core structure is assumed as one reason of this difference.[5] the characteristics and influence of core resonance is not enough clarified. We use a model transformer core to investigate the vibration characteristics and the vibration shape under three-phase excitation
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