Directivity of acoustic signals from partial discharges in oil

For partial discharges in oil, the relationship between apparent discharge magnitude, electrically measured in pC, and the acoustic signal amplitude from the same discharge, shows large variations. If the acoustic signal is detected with several detectors simultaneously, it is found that the acoustic amplitudes are correlated in a relatively narrow angle range only. For larger angular separation, the acoustic amplitudes are uncorrelated and not anti-correlated. From this observation and some theoretical considerations, some physical aspects of streamers in oil are illuminated. The streamer velocity may, for example, be estimated