Harmonics in transformers can have a significant impact on audible noise. Harmonics are multiples of the fundamental frequency and can be caused by nonlinear loads, such as power electronic devices and non-linear magnetic properties of transformer core materials. When harmonics are present in the transformer's operation, several effects on audible noise can be observed:
Increased core losses: Harmonics in the voltage and current waveforms can cause additional eddy current and hysteresis losses in the transformer core. These increased losses result in higher temperatures, leading to the expansion and contraction of core laminations. The magnetostriction effect caused by these fluctuations generates audible vibrations and noise.
Magnetostriction noise: Magnetostriction is the phenomenon where the magnetic properties of the core material change slightly as the magnetic field varies. This leads to physical movement and vibration of the transformer core. The vibration produces audible noise, especially when the frequency of the harmonic matches the core's resonant frequency.
Electromagnetic forces: Harmonic currents in the windings can create additional electromagnetic forces within the transformer. These forces can cause mechanical vibrations and audible noise.
Resonance effects: Harmonics can lead to resonant conditions in the transformer winding or core. Resonance amplifies the vibrations and noise, making it more audible.
Noise due to cooling fans: Transformers may have cooling fans that are sensitive to harmonic frequencies. Harmonics can cause fluctuations in fan speed, resulting in additional noise.
To mitigate the effects of harmonics and reduce audible noise in transformers, several measures can be taken:
Proper transformer design and selection of core materials with lower hysteresis and eddy current losses.
Shielding the transformer to reduce electromagnetic interference.
Installing line reactors or harmonic filters to limit the flow of harmonics into the transformer.
Implementing harmonic mitigation techniques in the power system to reduce the levels of harmonics generated by nonlinear loads.
Ensuring the transformer operates below its resonant frequency to minimize resonance effects.
It is important to consider these factors during the design and operation of transformers, especially when dealing with non-linear loads in the power system, to maintain acceptable levels of audible noise and ensure the transformer's reliability and longevity.