Comparison of the sensitivity of an acoustical and electrical PD-measurement on transformers in the laboratory and on site

Recently developed monitoring-systems, which measure electrically the occuring partial discharges (p.d.) in transformers, show the need for online- and offline-onsite-diagnostics. The limit in sensitivity which is reached using filters for sinusoidal disturbances and compensation for corona impulses is still not satisfactory. The acoustic p.d.-measurement is also a well known and reliable method often used by transformer manufacturers in testing. Laboratory setups have already shown a gain in sensitivity of the acoustic measurements in comparison to the electrical p.d. measurements. Taking into consideration the mechanical properties of a specimen, an improvement in the on site online sensitivity level can be achieved.