The extensive use of transformers in an electrical generation and
distribution system, has created noise problems by their necessary
location. From a noise view-point the ideal electrical substation would
be sited far away from populated areas. This unfortunately is not always
possible because of the scarcity of suitable land and other economic
design considerations. Also the problem is likely to increase rather than
decrease because of the modern tendency to build much larger transformer
units to overcome some of the economic problems. It follows, therefore,
one of the many aspects a designer must consider is the problem of noise.
A method often employed on
substation sites is to build a screen wall around the transformer, the
usefulness of the wall being mainly dependent upon its height and mass,
only small attenuations can be obtained from such a relatively expensive
treatment, and this is particularly true when comparing noise levels some
distance away from the screen wall. Much more effective than the screen
wall is total enclosure in which the noise energy can be contained.
Enclosures introduce problems in maintaining adequate electrical
clearances for high system voltages.
When designing a noise
enclosure there are five essential points to observe, (1) that the
material of the enclosure is suitable for noise reduction; (2) that the
transformer is not acoustically coupled to the enclosure; (3) that the
space between the transformer tank and the enclosure does not coincide
with half the wavelength of the highest frequency involved; (4) that all
openings in the enclosure are sealed or fitted with attenuators; and (5)
that all transformer connections are made as flexible as possible. The
main concern with the total enclosure method is to ensure that adequate
cooling air is provided at the transformer radiators and tank surface.
For larger transformers more cooling air is needed, and this can sometimes
be obtained by drawing cooling air into and out of the enclosure by means
of fans. A method of overcoming the large aperture problem, as well as
the fan noise, is to use tuned silencers.
A menu of
transformer aeroacoustic remediation protocols, acoustic performance
predictions and budgetary cost estimates are depicted on the following