Humming Noise in Electrical Transformers and Appliances

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SUMMARY

The humming noise observed in electrical transformers and appliances is primarily caused by the oscillation of magnetic fields generated at the power grid frequency, which is 50 Hz in Europe and 60 Hz in the US. This oscillation can cause loosely fixed components within devices, such as fans and mixers, to vibrate, producing sound at the same frequency. The phenomenon is not exclusive to AC circuits; it is a direct result of the alternating voltage switching every cycle, leading to sound emission from oscillating objects.

PREREQUISITES
  • Understanding of AC circuit principles
  • Familiarity with transformer operation and magnetic fields
  • Knowledge of sound wave generation and frequency
  • Basic electrical engineering concepts
NEXT STEPS
  • Research the principles of electromagnetic induction in transformers
  • Study the effects of mechanical vibrations in electrical appliances
  • Learn about sound wave propagation and frequency analysis
  • Explore noise reduction techniques in electrical devices
USEFUL FOR

Electrical engineers, appliance manufacturers, and anyone interested in understanding the acoustic behavior of electrical devices and transformers.

PhysicoRaj
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Every time I walk by the electrical transformer at the end of the lane, I hear a low humming noise(≈50Hz) that is continuous. I have observed this in all types of fans. I grab the hub so that it is not able to rotate and switch it on. Then I hear this hum. When the mixer/grinder chokes, it starts to hum in the same way, same frequency. What is the cause of this and does it hum in only AC circuits?
Thanks for any help in making me understand this.
 
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Voltage is switching every cycle of the power grid frequency, which is 50 Hz in Europe, 60 Hz in the US and one of those values in the rest of the world. Transformers generate magnetic fields with that frequency, and magnetic fields can move objects - if there is anything which is not perfectly fixed, it can move a bit in each cycle, with a frequency equivalent to the power grid frequency (or multiples of that). Oscillating objects emit sound.
 
Thanks. I understand now.
 

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