1..Could someone tell me in details why transformer with (15MVA...) sound????i dont know technical reasons??why generator transformer with the same specification never sound???
Just going on memory here - a generator transformer has a much higher operating voltage margin above normal voltage than a "normal" transfo. I think there is a supplement to standards applicable to generator transfo service.
A system or generator load shedding causes a (temporary) generator voltage jump which could overflux the transfo, causing high magnetization current (which causes transfo differential relay to trip).
Consequence is normal working flux density is lower in generator transfo - this reduces magnetostriction acoustic noise compared to a distribution transfo.
Another factor may be higher harmonic currents in the load of the distribution transfo - higher frequency sounds are more audible - the ear is more sensitive to 300 Hz than 100 Hz.
You could try recording the sound with a laptop computer and microphone [at 1 metre distance, say, from each transfo, similar location] and compare the levels/frequencies by doing a Fourier analysis on the recorded file. Many "spreadsheets" have a Fourier analysis function.
Re: TRANSFORMER DETAILS