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Transformer humming 4

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Emadshaaban1987

Electrical
Apr 30, 2020
58
hi experts ,

What are expected causes of a high transformer (50kva) humming (transformer is supplying UPS system)?
Transformer input current waveform shows a high wave distortion (33.0 THD), however the input waveform is pure with (1.60 THD) can this be the reason of high humming
 
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Magnetic forces are related to the square of the instantaneous current.
While the RMS current may be withing the capability of the transformer, the rectifier input of the UPS will be taking high instantaneous peak currents.
The resulting higher magnetic forces which are causing the hamming humming.

Bill
--------------------
"Why not the best?"
Jimmy Carter
 
Yes, the harmonic components in load currents combined with the interaction of the fundamental 60Hz or 50 Hz components, have a larger impact on the load noise level of transformers. In general, the "hum" intensity, is a function of the applied magnetically excited by an alternating voltage and current so that it becomes extended and contracted twice during a full cycle of magnetization. 

Two mechanisms combined are responsible for transformer audible hum noise:
[ul]
[li]Stray Magnetic Fields: causing the enclosure and accessories to vibrate.[/li]
[li] Magnetostriction: Induce mechanical vibrations by expansion and contraction of the lamination of the iron core due to the magnetic effect of alternation current flowing through the transformer coils.[/li][li][/li][/ul]
The enclosed link could provide further details on transformers audible humming noise.
NOTE: Perhaps the reason of high THDi content is because UPS design uses a 6-pulse rectifier. UPS design with a 12-pulse rectifier, and adding passive filters may reduce the humming audible noise to a more manageable level.












 
OK, I'll do it...

It's humming because it doesn't know the words...


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden
 
Hahaha! Nice one!
Back to the topic, the transformer noise you heard could be caused by loose core (core steel extend and contract when energized -->magnetostiction).
 
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