Why does the transformer make a humming sound?

The reason why the transformer makes a humming sound is closely related to the complex electromagnetic processes and physical phenomena inside it.

‌Magnetostrictive effect‌: The core material will undergo a slight mechanical deformation under the action of a magnetic field, and the frequency of this deformation is usually associated with the grid frequency (such as 50Hz or 60Hz). Since the magnetic flux in the transformer core is alternating, the core will be periodically affected by the magnetic force and expand and contract, thereby generating periodic vibration and noise. This is the main source of the humming sound.

‌Electromagnetic force‌: When current passes through the transformer windings, it generates a magnetic field around the windings. This magnetic field interacts with the magnetic flux in the core, generating an electromagnetic force on the windings. This electromagnetic force changes constantly with the current, causing the windings to vibrate slightly. These vibrations also travel through the air to create a humming sound.

‌Eddy current loss‌: In the transformer core, eddy currents are generated due to electromagnetic induction. When eddy currents flow in the core, they generate heat, which is called eddy current loss. Eddy current loss causes the core temperature to rise, causing thermal expansion and tiny vibrations of the core. These vibrations also spread through the air, forming a buzzing sound.

‌Internal core vibration‌: The tiny displacement of the core inside the transformer in the magnetic circuit causes vibration, which produces a buzzing sound‌.

‌Vibration transmitted by the shell ‌: The fixing bolts on the transformer shell tend to loosen after long-term use, which can cause the shell to vibrate, thus generating a humming sound‌.

‌Coil pollution ‌: When the transformer coil is contaminated, it is easy to generate electrical noise, thus generating a humming sound‌.

dry-type-transformer

By listening to the sound of the transformer, its fault state can be preliminarily judged:

1. Normal state: When the transformer is operating normally, the humming sound should be stable and uniform. If the transformer load changes, the volume of the sound may change, but the tone and frequency generally do not change.

2. Abnormal sound:

-Increased sound: If the humming sound of the transformer suddenly increases, it may be due to excessive load or overheating, or loose internal parts.

- Sharp or harsh sound: This sound may indicate partial discharge or insulation damage inside the transformer.

- Intermittent sound: If the sound becomes unstable or intermittent noise occurs, it may be due to problems such as poor contact, loose core or loose winding.

- Abnormal sound (such as popping): If you hear popping or other unusual sounds, it may be that a serious fault has occurred inside the transformer, such as a short circuit or insulation breakdown.

Through the above methods, you can preliminarily judge whether the operating status of the transformer is normal. If an abnormal sound is found, it should be stopped and checked in time to avoid further damage or safety accidents. Regular maintenance and inspection are also important measures to ensure the long-term stable operation of the transformer.