about transformers humming

[turkoman]

pls tell me if there is a difference between dry and oil type transformers in sight of transformer humming
and is it true that as the load increases the humming decreases and if dry type is worse than oil type with regard to this point. Also i wonder if there is a relation between harmonics and humming.. greetings

 

[dpc]

The hum is caused by vibration of the core (magnetostriction).

Dry type will generally be louder than oil filled of the same size. ANSI and NEMA have noise standards for transformers.

Harmonics could change the pitch and perceived loudness of the transformer hum.

Load current should not have too much effect, since the net flux in the core does not change much with load.

"The more the universe seems comprehensible, the more it also seems pointless." -- Steven Weinberg

 

[turkoman]

so pls tell me why dry types are louder tha oil types greetings friend

 

[rcw retired EE]

Oil dampens the sound. Dry type cores are exposed to the air. Oil-filled cores are inside a steel tank flooded with transformer oil.

The sheet metal enclosures on dry type transformers can also pick up the core vibrations and hum away.

 

[trosepe]

Dry type transformers with a temperature rise rating of 150 deg.C are louder than those with 115 deg. or 85 deg.C rise; 85 deg.C being the quietest. The lower temerature rise means more steel, more copper and less flux densities resulting in less noise.

 

[turkoman]

dry types work in higher temperatures than oil type_?