Transformer noise
In this case transformers are located in residential area, then the noise emanating from transformers may be annoying to the nearby houses. The hum, leading to noise, originates in the ferromagnetic core of a transformer.
The major cause of noise in transformers is the magnetostriction. When ferromagnetic transformer core is magnetized, the core length along the alternating flux decreases and inceases alternatively, with a corresponding increase and decrease of its cross-section. This phenomenon involving very small changes in dimensions of the magnetized core is called magnetostriction. As the steel laminations change their dimensions” alternately, the ferromagnetuc core vibrates and humming is produced. This humming traverses from the core to the transformer oil, to tank and then to the surroundings in the form of noise. The degree of hunming level depends on the flux density in the core. Greater the core flux density, greater is the tendency for humming in transformers.
The factors producing the noise in transformers are the following:
(1) The first cause of hum, and therefore the noise, is the magnetostriction.
(2) The details of core construction, size and gauge of laminations and the degree of tightness of clamping the core by nuts and bolts do influence the frequency of mechanical vibrations and therefore the noise in transformers.
(3) Joints in the core are also responsible for noise production though to a lesser degree.
Most of the noise emission from a transformer may be reduced (a) by using low value of flux density in the core,
(b) by proper tightening of the core by clamps, bolts etc.
(c) by sound-insulating the transformer core from the tank wall in case of large transformers or by sound-insulating the transformer core from where it is installed in case of small transformers.
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