Audible Noise Analysis And Control Of Power Capacitor

Power capacitor is the important equipment of High Voltage Alternating/Direct Current Transmission System. It can improve the voltage quality of power system and increase power transmission capability of transmission lines. There are lots of AC filters and shunt capacitor banks in Converter Station. This kind of capacitor element has the characteristics of large quantities, big capacity, high stack etc. The noise of those capacitor devices under ultrahigh voltage and super power is especially prominent and has come to be the main noise equipment in converter station. The noise emitted by the capacitor devices in converter station is very difficult to control because of the large amount, big capacity, high density and been exposed on the high capacitor stack. After other noise equipment has been adopted corresponding effective noise reduction measures the power capacitor noise becomes more and more significant.For the existing problem in power capacitor noise analysis, test, prediction and control etc. This paper starts with the internal structural analysis of power capacitor, expounds the mechanism of the capacitor-radiated noise; The properties of the capacitor’s noise spectrum are obtained by the acoustic-vibration coherent separation technology; Through the analysis of the natural vibration characteristics of the aluminum foil and shell of power capacitor the Multi-frequency Noise Jumping phenomenon is pointed out and analyzed; Based on the whole condition bridge loaded circuit of noise measurement on power capacitor the noise test platform is established in labrotery; The sound power level experimental method of power capacitor audible noise is determined and its measurement uncertainty is analyzed; The noise of capacitor unit as well as the noise of the capacitor stacks in convert station are calculated through the noise radiation efficiency; Based on the theory of combine micro-perforated panel, the low noise capacitor with broad band sound absorption structure is designed. The main contens are as follows:1) The development of power capacitor noise and the present research status with its main problems are introduced. The task and significance are discussed;2) Based on the internal structural analysis of power capacitor, the mechanism of capacitor-radiated noise is expounded. The capacitor-radiated noise is tested in lab conditions as well as converter station and the noise emitted by the power capacitor in converter station is separated with the acoustic-vibration coherent separation technology. The properties of the capacitor’s noise spectrum are analyzed, which has established the foundation for the research and control of capacitor noise;3) The method of variable separation is applied and the forced vibration equations of the aluminum foil and shell of power capacitor are established and solved. The natural vibration characteristics of the aluminum foil and shell of power capacitor are studied. And the Multi-frequency Noise Jumping Phenomenon is pointed out and analyzed, which provides a basis for the noise control of power capacitor.4) The deficiencies of present noise test loaded circuits for power capacitor are studied. According to the noise spectrum properties and the actual working condition that several frequencies loads are loaded simultaneously, the whole condition bridge loaded circuit of noise measurement on power capacitor is proposed. The loaded circuit can simulate the actual working conditions and realize fundamental and any number harmonics currents apply on the capacitor at a time. Based on the circuit the noise test platform is established, which creates the condition of noise test of power capacitor in laboratory.5) For the present chaotic situations of the test method and test specifications of power capacitor noise, the factors influence of the power capacitor-radiated noise is researched and the sound power level test method of power capacitor audible noise is determined. And further more, the measurement uncertainty is analyzed.6) The formula for calculating noise radiation efficiency is derived and the test method- vibration & acoustic transfer function method of noise radiation efficiency which can be adapted for experimenting in lab is obtained. The noise radiation efficiency curve of a power capacitor each surface is tested by the method and the noise of the capacitor unit as well as the noise of the capacitor stacks in convert station are calculated. The comparison between experimental and calculating results demonstrates the calculation achieves high accuracy.7) The noise reduction technology is studied, and according to the properties of the capacitor noise, based on the theory of combine micro-perforated panels, the low noise capacitor with broad band sound absorption structure is designed. The results of the contrast experiments of both low noise capacitor and ordinary capacitor prove that the effect of its noise reduction is obviously;8) In the end, the important outcome and conclusions of this dissertation are summarized and the main contribution of this paper is listed, and the future researches in this field are suggested.