Transformer Vibration Control and Transformer Noise Control

Transformer Vibration and Noise Control

Magnetostriction phenomenon in transformer core causes vibration and thus noise.  The noise propagates long distances thru the air and is perceived as air-borne noise.  The vibration transmits to the support structure and finds its way in neighboring spaces.  The transmitted vibration manifests itself mainly as structure-borne noise (and sometime vibration).  The noise caused by both mechanisms, i.e., air-borne and structure-borne, is for the most part tonal and thus annoying and tiring.

Air-borne noise abatement: The air-borne part of the noise can be abated by placing absorptive sound barriers around the units.  In outdoor installations, absorptive barriers minimizes the shadow effect of sound barrier walls, i.e., sound escaping from the top edges of the barriers.

Structure-borne noise abatement: When transformers are rigidly (not resiliently) mounted on the floor (or any other structure supporting them), their vibration will transmit to the support structure and find its way in neighboring spaces (rooms, offices, laboratories, etc.), causing an annoying, tiring, tonal noise. This structure-borne noise issue can be abated by:

  • Isolating the core and coils of the transformer from the ground/floor, using proper vibration isolators. In air cooled dry transformers this means isolating the core and coil from its support structure. For an oil filled unit it means isolating the core and coil from its tank base and isolate its tank base from the support structure.
  • Making certain all the connections to the surrounding are flexible. This includes incoming cables, busbars, stand-off insulators, etc. Note that any rigid connection from the vibrating transformer to a solid structure will transmit vibration.
  • Avoiding the use of a room, to house a transformer, with dimensions corresponding to half wavelength of the transformer vibration/noise frequencies. That is, stay clear of the room acoustic resonances being perturbed by the transformer.

Transformer vibration (and consequently noise) is caused by the magnetostriction of the core laminates (the extension and contraction of the core laminates when magnetized). Under alternating fluxes, this extension and contraction takes place twice during a normal voltage or current cycle, resulting in vibration to occur mainly at 120 Hz and its higher order harmonics (multiples of 120 Hz, i.e., 240, 360, etc). In addition, a lower magnitude vibration also occurs at 60 Hz and its odd multiples, i.e. 180, 300, etc.