Is the transformer noise normal?

Today the topic we will address is about something very common to see, but that leaves us in doubt: After all, why does the transformer snore? Was my equipment badly sized?

To answer these questions we need to understand the effects that occur on the transformer and that result in this phenomenon.

When the subject is “noise”, the first step is to understand the levels that the equipment can emit, for this there is a table (ABNT) that classifies the maximum noise level according to its power.

See below:

For small equipment there is a limit of 58 dB of noise that the equipment can emit.

Why does the transformer snore?

The reality is that every transformer emits noise as if it were snoring, what happens is that some equipment is designed with a very low noise level, (below 20 dB) that makes it inaudible to the human ear.

How does this effect occur?

Transformer noise is linked to three main factors:

1) Type of sheet used in the core:

When we define the type of sheet used in our project, we can choose the OG (oriented grains) and NOG (non-oriented grains) sheet, we have already talked about the subject of plates here on the blog, and as we know, NOG sheets support less induction than those OG, therefore we must respect the maximum induction limits that each type supports, the closer we get to the point of magnetic hysteresis of the sheet, the greater the noise emitted.

2) Induction used in the project:

The induction factor is a fundamental point in noise control so we have to be very attentive to the maximum induction levels supported by each type of plate to be able to adapt the equipment to levels tolerable by the standard.

3) Core tightening and stacking:

Equipment that has a non-uniform grip or a stacking without a precise fit in the transposition of the plates tend to show an increase of this effect.

See the picture below:

If we magnify the view to a microscopic level, logically, we will not see the magnetic flux, but, rather, we will see a small space between the sheets through which the magnetic flux acts, causing the sheets to be attracted against each other, generating noise effect.

As the magnetic flux travels through the sheet, it causes a slight attraction movement between them, generating a wave (and vibration) movement that causes noise in the transformer.

In addition to the natural effect of approximation between the sheets (caused by the magnetic flux) that causes a noise – similar when we hit with a ruler on the table – we also have another effect, caused by the friction between the sheets in the join point. That is why is so important to have a very linear cut, to fit the sheets better with a small microscopic space contact area between the grooves. This will significantly reduce the noise caused.

Was my equipment poorly designed?

This question is very interesting and generates a lot of doubt about the designing of transformer, but the answer is quite simple: if your equipment is noisy within the scale established by the standard, the answer is “No! Your equipment is not badly designed (from the perspective of noise)! ”

On the other hand, if you don’t have a tool capable of predicting such effects, you are at serious risk!

But how can I predict the level of noise that my equipment will have?

To predict this effect, you need to have a tool capable of crossing all the data related to induction, stacking, cutting of the plate and type of plate, to present the calculated noise.

This way you can have visibility in advance and not be surprised after the equipment is assembled.

As the image above shows, by calculating the noise level already in the design phase, it is easy for the designer to identify if the project is in agreement with the technical requirements or not.

How to measure?

The measurement process is currently defined according to distance and equipment.

The measurement must be carried out at a distance between 2 to 3 meters from the equipment, with a device called a decibel meter approved by the national standards board to make sure of the results obtained.


There are numerous variables that can influence the noise that the transformer causes. When it comes to production always having the machines with the revised setup, the process of assembling the monitored cores can significantly reduce the causes of noise in your equipment.

However, the biggest challenge is for the designer to be able to predict in advance the noise level that his project may have, and, through that, to make the decision on what to modify in the project to achieve the needs.

The good news is that there are more and more evolved technologies that make very difficult tasks easier and easier, making this unpleasant headache look like a beautiful and peaceful walk in the park on a sunny day!

see you soon!


  • William  Prange Theobald
  • ILTECH Operational Director with 10 years of experience in developing solutions for the Engineering area

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