04 April 2013

Magnetostriction:Transformer Noise

Noise In Transformer:

  • The basic cause for the noise in the transformer is due to magnetostriction of the sheets in the magnetic circuit (core of the transformer). Variations in the magnetic induction subjected to the sheets to periodic variations in the length, the amplitude which is in the order of microns per meter length.
  • The fundamental frequency with which these vibrations occur is double that of the system frequency, (for 60Hz frequency vibration frequency will be of the order of 120Hz) and also constitute numerous harmonics. Also various parts of the transformer, starting with the magnetic circuit (core) are liable to vibrate due to magnetostricition effect. 
  • The noise generated due to magnetostricition effect transmitted from the magnetic circuit to the tank of the transformer either through direct conduction to supporting points or through the oil and insulating material used in transformer. The transformer tank and the radiator radiate the acoustic noise or energy in to the ambient atmosphere 
  • Another source is due to the vibration of magnetic sheets perpendicular to the surface either at the edge or at the core packets, or at the joints between the leg and the yoke 
  • The current carrying windings is also a source of noise, however the amplitude of the noise is very less and is not detectable. 
  • Cooling fans and pumps employed for cooling the transformer is also acts as source of noise 

Methods to reduce Transformer noise: 

  • The main source of noise in the transformer is due to magnetostriction effect of the magnetic circuit or core. In order to reduce the noise cold rolled grain-oriented plant, with low magnetostriction and improved flatness is employed 
  • Ensuring uniform flux distribution and reduction in the cross flux also reduces the noise 
  • Elimination of the clamp bolt holes, use of resin impregnated glass-fibre bands instead of core bolts, gluing of core packets can reduce the noise 
These above specified remedial methods not only reduces the noise level by 5 to 10 dB, but also reduces the losses and no-load current

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