Acoustic emission measurements of ultrasound induced cavitation bubbles in aged insulating oils

The paper presents the behavior of ultrasound induced cavitation voids and bubbles in mineral insulating oils with different aging properties. At suitable values of signal amplitude and frequency many of cavitation bubbles were observed. Collapsing bubbles were responsible for broadband noise included in acoustic emission signal spectra. To represent the cavitation intensity a cavitation indicator based on power spectral densities of acoustic emission signal was proposed.