Why Do Transformers Hum?

A transformer has no moving parts, so why does it make a humming sound?

There are actually multiple causes of transformer noise. The main one is the Magnetostriction Effect. This is when the current that flows through the transformer’s coils creates a magnetic field. The magnetic field then changes the dimensions of the transformer’s iron core. The core expands and contracts with the alternating current, which causes a humming sound.

As the transformer ages, the layers within the core of the transformer begin to break apart and separate from one another. This causes the vibrations to get louder.

Transformer Noise Standards and Monitoring

Transformer noise levels are regulated by industry standards, with typical sound ratings ranging from 45 to 65 decibels depending on the unit's size and capacity. Commercial and industrial facilities must consider these ratings during equipment selection, especially when transformers are located near occupied workspaces or residential areas. Local noise ordinances often impose stricter limits than equipment specifications, making proper transformer placement a compliance issue rather than just a comfort consideration. Facilities that expand operations or add new transformers may find themselves violating noise regulations they previously met, triggering complaints and potential fines.

Excessive humming can signal developing problems before they cause transformer failure. A sudden increase in noise level often indicates loose laminations, failing core insulation, or deteriorating mounting hardware, issues that worsen rapidly under load. In critical operations like data centers, manufacturing plants, and hospitals where transformer failure means costly downtime, acoustic monitoring has become part of preventive maintenance programs. Maintenance teams use sound level meters and vibration analysis to establish baseline readings, then track changes over time to schedule repairs during planned outages rather than waiting for emergency failures.

Harmonic distortion from variable frequency drives, LED lighting systems, and other non-linear loads creates additional transformer noise beyond normal magnetostriction. These harmonics cause the transformer core to vibrate at multiple frequencies simultaneously, producing a more irritating buzzing sound than the standard 60Hz hum. Facilities with heavy electronic loads may need K-rated transformers specifically designed to handle harmonic currents without excessive noise or overheating.

How can you lower the volume?

• Unfortunately, you won’t be able to completely eliminate the sound your transformer makes, but you can minimize it. The most obvious way is to have your transformer installed in a low traffic area where it won’t annoy the people working for you.

• Install the unit on a solid surface of reinforced concrete which weighs at least 10 times as much as the transformer. Avoid mounting it in the corner, stairwell, or narrow corridor of your structure. These areas reflect and amplify noise.

• Try to have a 10-foot clearance on all sides of the transformer (except the ground).

• Tighten any loose bolts or screws which will add to the vibration if left loose. Also, mounting bolts for vibration dampeners should be removed after installation.

• Use noise dampening material such as acoustic tile to cover the walls of the transformer room. Oil barriers and cushion padding can help to insulate the transformer’s noise from the people working in the area.

Fan Noise

Fans are used to remove heat from the transformer. These fans add to the noise level. The more fans you use, the louder the noise will be. Other factors that affect the noise level are tip speed, blade design, and the arrangement of the radiators.

Are you having transformer issues, or any other electrical needs? Contact Landmark Electric today!