Why Do Transformers Hum?

We recently talked about transformers. Not the robots, but the electrical ones. In a follow up to that, we’re going to look at why transformers are noisy. We’re pretty sure everyone has experienced this noise at some point or other. You’ll find yourself next to an electrical room and hear a loud humming or whining sound. It’s not like the sound of a motor exactly. It’s just this constant, low sound.

For those unfamiliar, we found a good recording on Soundcloud below:


What Am I Hearing?

Let’s establish what actually makes the sound. Electricity itself doesn’t exactly make noise afterall, it’s just the conduction of energy through metal. Sure, lightning makes a good boom, but that’s totally different. When we talked about transformers, we mentioned that they’re pretty much solid parts, nothing inside moves. There’s no axles, hinges, shafts, or anything noisy. What part of that transformer are you hearing?

It turns out, the coils move. In most cases, the coils are too small to make a notable sound or the current going through them isn’t enough to make a loud noise. The transformers powering your HVAC equipment or converting high voltage AC current to your building’s 110 VAC however, are more than sufficient to make lots of sounds. It comes down to just how much material there is and how much energy is making it move.

As an aside.. If you put enough power into a transformer, it will probably end up exploding. We’re not talking about that much power.


Why Is Solid Metal Moving?

The freaky thing is that your transformer is made of mostly solid metal. We don’t often think of metal as something that ‘moves’ like a tree branch or a cloud. It’s a solid substance, so therefore it shouldn’t move unless we pick it up and move it. This all comes back to those pesky electromagnetic fields that our whole transformer relies on to actually do its job.

The power goes inside, the field forms, and then is converted back into electricity.  There’s two other factors here: magnetic things like to push things with other charges around and AC power causes lots of changing charges. We create the magnetic field, it’s going to want to push or pull the metals apart. We put in AC Power, which is constantly oscillating in charge and we allow that field to change direction 50-60 times per second. The metal is being forced to move and vibrate microscopic amounts by the fields around them.

The vibrating metal creates the humming sound. It works pretty much exactly the same as the strings on a violin or a harp. The instrument vibrates, disturbs the air, and creates a sound wave for you to hear. Given that power is well regulated and controlled, it’ll always be that 50-60hz oscillation and therefore, always that same hum when the transformer is on.

You can hear a raw 60hz frequency from Soundcloud below:

Your transformer of course, is subject to so many other factors. Impurities in the metal, minute changes in power, and even other local magnetic fields cause your transformer’s hum to be more unique than a pure input signal.

The Wrap Up

So, did we get something wrong? Is there something you want us to cover? Let us know in the comments below!



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