Measurement of acoustic emission velocity in natural ester

Paper presents velocity measurement results of acoustic emission (AE) signal propagating in natural ester. The velocity of AE wave is crucial especially in methods used for partial discharges (PD) localization and its value may influence the location, which is calculated based on arrival time. Experimental works were performed using piezoelectric transducer for AE signal generation (transmitter T) and hydrophone for AE detection (receiver R) immersed in an elongated tank filled with liquid dielectric at various distances d between T and R. The velocity was calculated based on time of arrival (ToA) of the AE signals propagating from T to R and distance d. The transmitted AE signal was modulated using a frequency range from 40 Hz to 400 Hz what enabled to determine the velocity values within the analyzed spectrum. Based on the gathered results it was stated that velocity of AE signal propagating in the considered oil decreases while increasing the distance between T and R. Furthermore the calculated values depend strongly from the frequency of the AE signal. For an exact calculation of location of PD occurring in this type of dielectric the appropriate value of velocity should be considered. It is also recommended that a correction factor related to distance between PD and AE sensor is taken into account.