Harmonics in transformers can have several effects on audible noise, especially at high frequencies. Audible noise in transformers is primarily caused by magnetostriction and electromagnetic forces acting on the transformer's core and windings. Harmonics can exacerbate these effects and lead to increased audible noise levels. Let's delve into some of the effects:
Increased Core Losses: Harmonics, especially odd-order harmonics, can lead to increased core losses in the transformer. These losses cause the core to expand and contract rapidly, leading to magnetostriction—a phenomenon where the core material experiences mechanical vibrations. These vibrations can generate audible noise, which becomes more prominent at higher frequencies.
Winding Vibrations: Harmonics in the input voltage or load current can cause increased electromagnetic forces on the transformer windings. This can induce vibrations in the windings, which contribute to audible noise generation. Higher frequency harmonics can result in higher-frequency vibrations, leading to noise at frequencies that may be more perceptible to human ears.
Resonance Effects: Harmonics can excite resonant frequencies of the transformer's mechanical structure, such as the core, windings, or support structure. When these components resonate, they can vibrate more intensely, causing additional audible noise.
Sound Level Modulation: The presence of harmonics can modulate the audible noise level of the transformer. Depending on the harmonic frequencies and their interactions, the noise may become more or less pronounced at certain frequencies or time intervals.
Cooling System Noise: High-frequency harmonics can also affect the cooling system of the transformer. Cooling fans or pumps may generate additional noise when they respond to the harmonic frequencies, contributing to the overall audible noise.
To mitigate the effects of harmonics on transformer audible noise, various measures can be taken:
Filtering the input power to reduce harmonics.
Using low-noise transformer designs and materials.
Applying mechanical dampening to the transformer's core and windings.
Opting for specialized coatings or insulation to reduce magnetostriction effects.
Implementing advanced transformer design techniques to minimize vibration and audible noise.
It's important to note that transformer design, load characteristics, operating conditions, and maintenance practices all play a role in determining the level of audible noise. Addressing harmonics and their effects is just one aspect of ensuring low-noise transformer operation.