noise (hum) vibration in high current switchboards 1

[rodelec]

We have installed numerous Switchboards in a telephone exchange with ratings from 1000 amps up to 6000 amps. Some of these switchboards as well as other existing switchboards "hum" when under load. The hum appears to be a low frequency so we assume it is at supply frequency (50Hz). Harmonics doesnt appear to be an issue. The vibration is being transmitted through the Switchboard and submains. Whilst it is not unusual for humming, this project seems to have more of a problem than what we have come across in the past. The supply transformers are also very loud. Sub Switchboards (1000 amps at 50% load) over 100 mts from supply also have the problem.
Any comments or suggestions about the possible reasons and solutions would be greatly appreciated.

 

[electricpete]

Some of these switchboards as well as other existing switchboards "hum"... Any comments or suggestions about the possible reasons..

Because they don't know the words?

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[itsmoked]

The materials are driven by the magnetic fields that are sinusoidally varying. The loudness will be a function of the local metal structures and other field generating conductors. How the cables are routed, how they are anchored, and 'what' they are anchored to.

Several of these aspects can be because 'X' brand panels are shaped or mounted so as to be easily acoustically driven at the line frequencies. Also the building can have wall designs that provide no acoustic damping or in fact can and do actually increase the acoustic coupling to the air.

These are some of the reasons one facility may be noisier than the next.

There might be higher current loading then previously experienced in other installations.

Especially noisy transformers can be due to different brands and looser windings or laminations.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[DaveScott]

//Especially noisy transformers can be due to different brands and looser windings or laminations.//
I agree, together with the metallurgical properties of the silicon steel in the laminations, and I suspect that loose windings and laminations may (but I have absolutely no prior experience or evidence of this) contribute to the generation of harmonics in the secondary side.
Maybe some other members might comment on this.

 

[TheBlacksmith]

Because they don't know the words?

I've been dying to post this several times - thanks electricpete

 

[Snoball]

Watch your "Sawdust" piles under things.