Abstract
Power capacitors are widely used in power transmission systems. During their operation, an electric force acting on the electrodes of the power capacitors actuates mechanical vibrations and radiates an audible noise. Considering a power capacitor as a general system, the frequency response with the electric force as the input and mechanical vibration as the output have been measured by engineers in recent years and used to evaluate the acoustic and mechanical features of products. Accidentally, it was found that the frequency of the capacitor vibration was not consistent with its excitation due to electro-mechanical coupling. This electro-mechanical coupling had not been considered in previous vibration models of power capacitors. Therefore, a new vibration model of power capacitors was built up in this paper and a so-called multi-frequency vibration characteristic was revealed. A theoretical analysis showed that the electric force and mechanical vibration of the power capacitors were coupled, which resulted in the multi-frequency vibration. The vibration frequency response was measured and the result was consistent with the vibration model proposed in this paper. Once the frequency of the electric force was near half the natural frequency of the power capacitor, a predominant multi-frequency vibration was triggered and the power capacitor was in a superharmonic resonance.
Highlights
The audible noise of power capacitors originates from mechanical vibration, which is excited by an alternating electric force inside the capacitor cores [1–3]
When the electric force angular frequency ω E approached the natural frequency of the capacitor structure, i.e., cos(kl) = 0, Equation (10) became infinity and the power capacitor was in mechanical primary resonance with a series of natural frequencies as: c π ωn = ( + iπ ) i = 0, 1, 2, 3
A significant peak appeared in the vibration measured natural frequency of 1180 Hz, a significant peak appeared in the vibration frefrequency response curve, indicating superharmonic resonance excited
Summary
The audible noise of power capacitors originates from mechanical vibration, which is excited by an alternating electric force inside the capacitor cores [1–3]. The right hand side of the partial differential equation demonstrates that there was a coupling between the mechanical vibration and the electric field of the capacitor core, which could be regarded as a time-dependent elastic modulus of the capacitor core structure. This coupling could generate the capacitor to produce more high-frequency components of the mechanical vibration and cause the frequency spectrum to become more complex
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