Transformer Noise


Thread Starter


Our company faced a problem on a 4160 to 600 volt dry type transformer 1000 kva wye/delta solidly grounded on the primary. the problem is big noise which can be heard outside even with all the doors closed in the sub. the noise is like 2 seconds off 4 seconds on, which is way lower than 60 cycle. is not humming noise. Any body who has experience in this matter please answer.
Can you check the 600 V 3 phase lines and ground with a clamp on amp meter? Does the noise change with any current change in the wire?

The next idea is the sheet metal of the cabinet my be too close to the core of the transformer. The sheet metal acts just like a speaker cone.

William Hinton Sr. Electrical Engineer @

We have had noise and excess heating in the DELTA secondary from 2 causes:
1) High harmonic current circulating in the secondary safely being converted to heat. Two things have caused this:
a) A voltage imbalance on the primary
b) High harmonic distortion in the load on the secondary (greater than 5%)

2) Dynamic breaking when decelerating an AC motor with an adjustible speed or soft start motor drive. Some drives use single phase power for dynamic breaking (Allen Bradley's SMC does this)

The cause of our noise was evaluated by the transformer manufacturer for many days with no ill effects so we stopped being concerned bith it. Our transformer is still running just fine 5 years later.

I hope this helps.
Are you near an older telephone building. These systems use a brush type ringing current generator and the frequency of ring on/off is what you are hearing. They may be unbalancing the primary from another sub.

Bob Peterson

Sounds like maybe its overheating, or you may have some intermittant load causing the noise. A good electrician should be able to run it down. i concur with the response above and suggest consultation with someone competent in such things.
The problem is the noise does not present when they are here. It was heard once last year and once this year. As soon as I deenergise it and reenergize it again the noise gone. I am still waiting for another one.
We performed the transient study on the secondry

we got 3.5 % hormonic voltage distortion and 1.5 % current distortion. whenn we take off the load the frequency of the noise will change not the ammplitude.
Dry type transformers of this size have insulation stacks, spacers and the insulation surrounding the windings under fairly high pressure. In turn the steel rods applying this pressure are under high tension. Here it comes most likely down to one of two things: The support for the transformer core is not substantial enough, allowing a very low resonance frequency to build, or the unit has experienced a high load (or even mechanical) shock resulting in loosening of the above mentioned compression stackup. The advice you got before stands, you need professional help from someone familiar with that size equipment and apparatus repair shop methods.


Matthew Hyatt

Since this is not happening on a regular basis, you may want to geta power analyzer, monitor the load current for a while and when it does happen gather as much data as possible. Otherwise, I would not worry about it unless you are observing secondary voltage probelsm, or other related problems with equipment.