In school years, physics classes gave us the concept of magnetostriction. Not everyone, however, then it was interesting. Let us try now to return to the topic and briefly outline the essence of the process. First, let's recall how a transformer works.
The figure shows the simplest device consisting of a primary winding (A), a secondary winding (B) and a core (C) - a magnetic core assembled from metal plates or from a material having ferromagnetic properties.
When an alternating voltage is applied to the primary winding (A), a current begins to flow in it, under the influence of which a magnetic flux (Ф) is formed in the core (C), which induces a current in the secondary coil (B), to which the load is connected. A voltage conversion takes place, the value of which at the output will depend on the ratio of the number of turns of the primary and secondary windings. The frequency will remain unchanged.
Magnetostriction is a physical process of changing the volume and size of a body under the influence of a magnetic flux passing through this body. Subject to change are materials with pronounced magnetic properties, from which cores for transformers are produced.
The figure shows the frequency of the process of compression and extension of the core per cycle of magnetic flux change. Changes in the size of the magnetic circuit lead to air vibrations. Waves are formed having a frequency in the sound range (50 Hz). This is the very buzz that accompanies the normal operation of power transformers. In IIP (switching power supplies), such noise is absent, since the frequency of waves generated in the process of oscillations is not included in the range audible by a person.
Factors Affecting the Level of Hum
How much the transformer is noisy depends on:
- degree of workload;
- overall dimensions;
- physical characteristics of the material of which the magnetic circuit is made.
An overloaded transformer will buzz louder than operating at rated load. And the characteristic noise arising from the operation of large power converters in substations is normal.
Causes of side sounds in the transformer:
- When the winding of the coil is loose, under the influence of magnetic flux, which tends to shift the windings of the device relative to the core, vibration occurs, accompanied by a hum.
- In the process, with poor fitting of the core plates and the formation of gaps between them, vibration occurs, accompanied by a metallic ringing, subsequently noise.
- In case of violation of the integrity of the wires of the winding coil can spark. The process is accompanied by claps. With powerful discharges, the sound is more intense.
- A loose transformer and its parts also vibrate and hum.