Electrical Transformer Noise Reduction and Operation | Every transformer does make some noise, but it becomes conspicuous when the size is large. The noise are hum is due to the fact that the core, which is made up of thin laminations, vibrates because of the alternating magnetic flux, and therefore expands or contracts ever so slightly with each cycle magnetization this causes the audible hum. The contraction caused due to magnetization is called Magnetostriction.
Electrical Transformer Noise Reduction and Operation
The transformer core must be tightly clamped together to reduce the hum. The flux density should also be reduced as much s possible, but there is a practical limit to this. Sometimes, under unfavorable conditions of poor design or construction, the hum gets multiplied 100’s of times due to resonance. This should not be permitted.
The noise and hum reduced by large transformers in urban areas often reached such high values has to be a source of disturbance and annoyance to the people living nearby. The noise level decreases quickly with distance. i.e. By some 6 dB for every doubling of the distance, so that at about 200 feet the reduction could be about 26dB. Transformer should therefore be located as far away from residential areas as possible.
Where they have to be located in heavily populated places, one method adopted to reduce the noise is to install the transformer inside an enclosure which is made sound proof. Brick walls lined with acoustics material are quite effective and all connections should be by underground cables. When the size is large and the voltage is high, the radiators could be mounted outside the enclosure and connected to the transformer by flexible pipe connections. The transformer itself is mounted on resilient pads.
Air inlet and outlet ducts are lined with sound absorbing material to deaden the noise of ventilating fans which should admit sufficient quantity of air to take away the heat produced by the transformer. It is not possible to build conventional enclosures around the large transformer, because of the high voltage bushings and clearances required.
This difficulties has been solved by M/S AEI for a 180 MVA outdoor transformer by building an acoustic enclosure comprising a double wallet sheet shell, filled with viscous compound, round the transformer tank leaving out the bushings and the radiators. Sufficient space is left inside to permit normal maintenance. The transformer is mounted on one 1 inch thick cross ribbed neoprene rubber mats to limit the ground borne noise.
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