Wondering Why?

Why do transformers hum?

Most of the transformers produce some sounds that are audible at the current frequency based on which they operate. The transformers that are functioning based on the utility power in the United States are 60 Hertz. This sound is because of the wire that is present in the transformer coils and the steel present in the core of the transformer which vibrates at 60 Hertz due to the interaction of the component’s magnetic fields. The sound is also found to be produced due to the magnetostriction where the steel core expands and contracts because of magnetic field fluctuation. The iron and ferrite transformer core increases in length and decrease when it is operating at the frequency of 20 to 20,000 Hertz of the applied AC voltage. This process is called as magnetostriction. In this process, the air is pushed back and forth at this frequency creating a humming sound. Transformers which do not have a core will not generate this sound.

A transformer’s core is magnetic steel made with many laminations. These laminations are grouped into one and stacked on a frame. They tend to work based on the principle of electromagnetic induction. The transformer’s core functions for laminations allowing the magnetic flux that is passing through it. The magnetic flux makes it vibrate leading to the humming sound. Abnormally, the loud, humming sound might be because of a loose interaction with the laminations. The magnetic field will make the movement of the windings and laminations inside the transformer at the rate of the power line which is 60 Hertz.

Actually, a perfect transformer will not produce a humming sound. The transformer coils are joined with each other through metal plates which pass the magnetic field. The poles of the alternating current change the direction, and the magnetic field also will change the direction. This might probably allow the plates to wobble which is the same as the clock rate of the alternating current.  The transformers do hum, but some are very loud and abnormal. The reasons might be due to an insecure mounting on the resonant surface or a loose lamination due to a poor design or possibly the presence of old parts and the development of rust in-between the core laminations that makes the noise when the laminations vibrate on one another.


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