Why Do Transformers Hum?
A transformer hum should be low and consistent. Learn the natural causes for a transformer hum as well as noises that may prompt further investigation.
How To's
A transformer hum is usually normal. Most transformers produce a low, steady humming sound caused by magnetostriction in the core and natural vibration of surrounding components. However, sudden increases in noise, rattling, popping, or irregular buzzing may indicate overload, loose components, or internal faults that require investigation.
Understanding the difference between normal transformer sounds and concerning ones can help you identify potential issues early and maintain reliable operation. Let's take a closer look at why transformers hum and what certain noises may be trying to tell you.
What Causes Transformer Humming?
Transformers hum primarily because of magnetostriction and natural resonance. Magnetostriction causes the transformer core to expand and contract as the magnetic field changes. Natural resonance occurs when these vibrations transfer to surrounding structures, amplifying the sound.
A healthy transformer hum should be low, consistent, and relatively calm.
Magnetostriction
Magnetostriction is a natural occurrence in transformers. (It’s also a clunky word that we don’t recommend attempting before morning coffee…)
During operation, a magnetic field activates as electrical current flows between the transformer coils. At the same time, the transformer’s metal core expands and contracts, creating a humming sound. This phenomenon is called magnetostriction. Learn more about how transformers work.
The surrounding components of the core also vibrate, adding their noise to the mix. The combined buzzing or droning sound makes up the transformer’s hum. A healthy transformer hum should be low, consistent, and calm.
Natural Resonance
A second reason transformers hum is natural resonance.
Transformers are typically installed on concrete pads, utility poles, steel structures, or inside buildings. As the transformer vibrates during operation, those connected structures can vibrate as well.
When these components vibrate at similar frequencies, the sound can become more noticeable. This effect is known as natural resonance.
Although the hum may seem louder, natural resonance alone is not necessarily a cause for concern.
Is Transformer Humming Normal?
Yes. A low, steady hum is a normal part of transformer operation.
Various organizations have published industry standards for transformer noise levels. Take a look at the NEMA and IEEE industry standards for transformer noise.
NEMA Standards for Liquid-Filled Transformers
These are industry sound levels for liquid filled transformers like padmounts, substations, and polemounts.
One thing to keep in mind here: unless otherwise specified, transformer NEMA sound levels are established at no load. This means that if you measure the unit’s sound while the transformer is both energized and under load, you may find the sound louder.
IEEE Standards for Dry-Type Transformers
Here are the IEEE standards for low voltage and medium voltage dry-type transformers.
Transformer sound levels are typically measured in A-weighted decibels, or dB(A), which reflect how the human ear perceives sound.
For comparison:
- A quiet office is approximately 40 to 50 dB(A).
- Normal conversation averages around 60 dB(A).
- Many distribution transformers operate within the 56 to 68 dB(A) range defined by NEMA standards.
What are Ways to Reduce Normal Transformer Noise?
Even if your transformer produces humming sounds within the standards listed above, the noise can still be a lot to handle. Especially if your transformer is indoors. Below are a few ways to reduce the amount of sound your transformer produces.
Add Walls
You can surround the transformers with thick walls or even put the unit in its own room. Many offices or manufacturing buildings have a dedicated electrical room where they store and protect their equipment. The additional insulation from these walls will reduce the sound you hear.
Install Anti-Vibration Pads
Some types of transformers can sit on anti-vibration pads. These pads create a gap between the transformer and the ground. They also absorb the vibration of the transformer itself. Both of these factors decrease the overall level of sound.
What Transformer Sounds Should Raise Concern?
Maddox Field Insight
In our experience evaluating transformers, the most concerning situations are not necessarily the loudest ones.
Any sudden change in transformer noise deserves attention.
If transformer noise exceeds expected levels or shifts from its normal operating pattern, investigate the cause. Some sounds may indicate minor maintenance issues, while others could point to serious internal problems.
In particular, irregular buzzing, crackling, popping, or noises resembling internal arcing (this will sometimes sound like a weed whacker inside your transformer) should never be ignored.
Several conditions can cause a transformer to become louder than normal:
Core Saturation
Core saturation occurs when the transformer’s core can no longer efficiently handle the magnetic field. Overvoltage conditions or excessive loading can contribute to saturation, increasing vibration and noise levels.
Transformer Overload
When a transformer carries more current than it was designed to handle, the windings and core can overheat. This additional stress can alter normal vibration patterns and create a louder or less consistent hum.
Loose Components or Mounting Hardware
Loose components, mounting hardware, or structural connections can create rattling and amplify vibration.
Routine maintenance inspections should include checks for loose hardware and signs of excessive movement.
Wear and Aging
Over time, normal wear can affect the transformer's structural integrity. Aging components may contribute to changes in sound characteristics that warrant closer evaluation.
Transformer Sounds: What’s Normal and What Isn’t
What Should You Do If The Noise Changes?
If Transformer Noise Changes Unexpectedly:
- Check for signs of overheating.
- Inspect mounting hardware for looseness.
- Verify that loading remains within design limits.
- Review whether protective devices have operated.
- De-energize the transformer if you hear popping, crackling, or suspected arcing.
- Consult a qualified transformer technician if concerns persist.
Conclusion
We hope the reasons for transformer noise are now a little clearer. Understanding transformer sounds along with routine transformer maintenance will tell you if a unit should be repaired or replaced.
If you’re unsure of whether a transformer noise is normal, you can always reach out to us. Maddox can tell you what to expect. We can also help you investigate anything that doesn’t sound quite right. And, we can help you with any needed repairs.
If you have concerns about your transformer’s noise, fill out the form below!
