Why there is humming noise in transformer.

Transformer makes some noise like humming or buzzing. In some case the noise is very much loud. This is mainly because of dc offset current in the supply current and defect in the transformer core structure of the

Humming noise in transformer- why

Normal sinusoidal alternating current produces evenly flux but the direct Current component (DC offset current) in the supply current creates some fluxes too. This extra magnetic flux attracts or distracts the core structure of transformer. This creates the humming or buzzing noise. Thus this is a mechanical noise.


Transformers that are experiencing dc-offset problems are usually noticed because of objectionably loud noise coming from the core structure. Industry standards are not clear regarding the limits of dc offset on a transformer. A recommended value is a dc current no larger than the normal exciting current, which is usually 1% or less of a winding’s rated current.

Other reason of noise in transformer

  • Resonance of the box & radiators. This resonance occurs due to the abnormal changes of the source current frequency.
  • Defect in core physical structure mechanism.
  • Core is loose.
  • Grounding plate is loose.
  • Noise due to static discharge due to poor grounding or inadequate grounding plates.

power transformer
7.5 MVA unit 72 kV/6 kV Transformer

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