Harmonics in a transformer can have a significant impact on its audible noise. Audible noise in transformers is primarily caused by magnetostriction and the electromagnetic forces acting on the transformer's core and windings. These forces cause physical vibrations in the transformer, which result in the production of sound waves that can be heard as noise.
When harmonics are present in the transformer's operating conditions, they can exacerbate the audible noise for several reasons:
Increased Core Flux Density: Harmonic currents, which are multiples of the fundamental frequency, can lead to increased core flux density. Higher flux densities in the transformer core can intensify magnetostriction, a phenomenon where the core material changes shape slightly with each AC cycle, generating audible vibrations and noise.
Additional Copper Losses: Harmonic currents flowing through the transformer windings cause additional copper losses. These losses lead to higher temperatures, which can affect the mechanical properties of the transformer's components and increase the magnitude of vibrations, hence contributing to audible noise.
Resonance Effects: Harmonics can cause the transformer's mechanical components to vibrate at specific frequencies, leading to resonance effects. Resonance amplifies the vibrations and noise, making it more noticeable and potentially damaging to the transformer.
Structural Vibrations: Higher harmonic frequencies can induce additional structural vibrations within the transformer. These vibrations can resonate with other components of the transformer, such as the tank or the winding supports, creating further noise.
Winding Vibration: Harmonic currents can induce vibrations in the transformer windings due to the skin effect and proximity effect. These vibrations can contribute to the overall audible noise level.
To mitigate the impact of harmonics on audible noise in transformers, engineers may take several measures:
Using low-noise core materials with reduced magnetostrictive properties.
Employing dampening techniques to absorb and dissipate mechanical vibrations.
Implementing proper grounding and filtering to reduce the flow of harmonics in the transformer.
Designing transformers to handle harmonics, considering factors such as winding construction and cooling methods.
Ensuring that the transformer is operating within specified limits for harmonics and load conditions.
Overall, harmonics in transformers can be a significant factor contributing to audible noise, and careful consideration is necessary during the design and operation phases to minimize their impact.