Transformer Humming
Transformer Humming
(OP)
Hi All,
This is just a curiously question more than anything.
I often hear much older and experienced engineers refer to the transformer humming as a 120Hz sound (on 60Hz system) or 100Hz sound on a 50Hz system which makes sense but in most cases these transformers are 3-phase units which in my mind would be a 360Hz or 300Hz sound. What am I missing?
This is just a curiously question more than anything.
I often hear much older and experienced engineers refer to the transformer humming as a 120Hz sound (on 60Hz system) or 100Hz sound on a 50Hz system which makes sense but in most cases these transformers are 3-phase units which in my mind would be a 360Hz or 300Hz sound. What am I missing?
"Throughout space there is energy. Is this energy static or kinetic! If static our hopes are in vain; if kinetic — and this we know it is, for certain — then it is a mere question of time when men will succeed in attaching their machinery to the very wheelwork of nature". – Nikola Tesla






RE: Transformer Humming
RE: Transformer Humming
To answer VTer's question: If you have three sound sources that each emit a 100 (or 120) Hz tone, then all you will hear is the sum of those tones. And that is still a 100/120 Hz tone.
Another situation is when you run, say, a DC motor from a thyristor controlled rectifier that is connected to a three-phase trasformer. Your armature current then contains 300 (or 360) Hz components (because of the six-pulse rectification) that emit the typical "thyristor sound".
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Transformer Humming
http://en.wikipedia.org/wiki/Magnetostriction
David Castor
www.cvoes.com
RE: Transformer Humming
RE: Transformer Humming
Also, the audible sound produced by fan-assist cooled (FAC) transformers is partially due to the energizing of the core by the alternating voltage applied to the windings and also by the fans forcing air through the coils. The noise generated by the core, and whose fundamental frequency is twice the frequency of the applied voltage, will create audible sound will be present even under no load conditions. The vibrations producing audible sound can occur in the core, coil, mounting, housing, and in the conduit. The transmission of sound from the transformer can be by various media such as air, metal, concrete, wood or any combination. Amplification of audible sound can occur in a given area due to the presence of reflecting surfaces.
Transformer hum also arises through the vibration caused when the load current passes through the windings, interacting with the leakage flux it generates. This "load noise" level is determined by the size of the load current.
In IEEE C57.94, Recommended Practice for Installation, Application, Operation, and Maintenance of Dry-Type General Purpose Distribution and Power Transformers, they tell us that the audible sound produced by transformers is due to energizing of the core by the alternating voltage applied to the windings. This creates vibrations whose fundamental frequency is twice the frequency of the applied voltage. The vibrations producing audible sound can occur in the core, coil, mounting and in the housing. The transmission of sound from the transformer can be by various media such as air, metal, concrete, wood or any combination. Amplification of audible sound can occur in a given area due to the presence of reflecting surfaces.
RE: Transformer Humming
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...