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Join Date: Oct 2013
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Instrument Transformer (CT/PT)

10/27/2013 1:02 AM

can anybody tell the reason for the humming sound from 110kv potential transformer..(it is not a CVT, Checked the primary and secondary earthing and found healthy,checked the tan delta value -1.3)

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#1

Re: instrument transformer(CT/PT)

10/27/2013 1:56 AM

Humming mostly occurs in the core. Some gap between the iron may cause that. Also the same when the windings are a bit loose. (almost nothing) Humming is still OK, vibrating is worse. A third reason can be that the core is close to saturation. You can check this with less load on the transformer.

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#2
In reply to #1

Re: instrument transformer(CT/PT)

10/27/2013 6:25 AM

its just a bus PT in a 110kv bus, so a slight loading only always, and no other pt's having this sound,

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#3

Re: instrument transformer(CT/PT)

10/27/2013 2:48 PM

It's humming because it's happy.

You give no usable information and expect an answer, dream on!

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#4

Re: Instrument Transformer (CT/PT)

10/27/2013 11:01 PM

It does not know the words.

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#5

Re: Instrument Transformer (CT/PT)

10/28/2013 12:54 AM

when it's humming, it's ok... when you hear La,LaLaLaLa, La,La,La!

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#6

Re: Instrument Transformer (CT/PT)

10/28/2013 8:34 AM

Typically humming noises from transformer are caused by loose laminates. The frequency of which should be close to the line or operating frequency of the device. This laminates may have loosened up during transport or when ever it was unnecessarily exposed to some strong vibrations.

Re-tightening all fasteners / bolts used may solve the humming problem. Putting some non-electrically conducting wedges in-between spaces or gaps may also help minimize the noise. The last thing you may try, if the transformer is mounted close to some other unit(s) is to re-position or re-orient its mounting.. at times by re-positioning the device, there is a tendency for those stray energies to cancel each other electromagnetically. You may have to do all the above when the power is OFF!

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#7

Re: Instrument Transformer (CT/PT)

10/28/2013 9:07 AM

I take it that the humming is the only problem since you have not noted any harmonics or faulty voltage transients. I assume it is with the frequency of the system. Some transformers are just noisy and that could be from faulty manufacture, shipping damage, or handling damage. It is usually a resonance or direct core noise due to looseness or a mechanical stress that is putting pressure on the core. If the PT is withing warranty, call the manufacturer. If it is out of warranty and is providing a clean signal on the secondary, then you will have to decide whether you can live with the sound. If you cannot, consider purchase of a replacement and keep this one for a spare. Repair of a PT is not usually possible and when possible is not usually cost effective. If an outage is in the future and you want to be sure, swap the PT with one from one of the other phases which doesn't make noise. ( I am assuming that it is a single phase PT on a 3 phase system) If it is a 3 phase PT, which is very rare, then the noise could be coming from a harmonic which would be usually 3 or 5 times the frequency of the system. If that is the case then look at the loads. Solid state drives with unbalanced phases are frequent causes. Single phase loads will cause third harmonics. Three phase PT's are usually repairable, but as I said are extremely rare. If you do have a three phase PT, consider a short outage, (minutes) in which the loads on the system are dropped. If the noise stays the same it probably will not mean an outright failure of the PT. If the noise stops, the problem is not in the transformer, but in the load. That is if you are correct and it is a humming sound. If it is a spitting or arcing sound run away from it now and de-energize.

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#8

Re: Instrument Transformer (CT/PT)

10/28/2013 3:32 PM

Aside from tightening loose coils and laminate with wedges and by tightening screws...if it can be removed or turned off while drying, I've often cured this problem with 'glyptol', a high solids varnish used for insulation in motors and transformers.

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