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The intensity of acoustic cavitation noise in thermally aged insulating oils

The paper presents some observations of ultrasound induced cavitation phenomenon in mineral insulating oil. The acoustic cavitation phenomenon was generated at different signal frequencies and rms voltage value supplied to round piezoelectric transducers. Used transducers have created a high energy acoustic field in prepared insulating oil samples. The acoustic emission signal contains a broadband noise and a fundamental frequency component and its harmonics, produced by the direct driving acoustic field. The paper presents the spectral analysis of acoustic emission signal observed during acoustic cavitation in insulating oils with different aging times. To emphasize the changes in acoustic cavitation intensity a series of thermally aged insulation oil samples was prepared. The main application expected with created cavitation measurement system is to develop a diagnostic tool for the aging of oil, based on the hypothesis that the measured cavitation intensity and spectrum could be affected by aging. Previous published measurements showed some relationship between insulating oil aging process and changes of acoustic emission of cavitation. The paper introduces a method of evaluation of the relationship between the changes of used acoustic cavitation intensity factors and the insulation oil aging time.