Directivity of acoustic signals from partial discharges in oil

For partial discharges in oil, the relationship between the apparent discharge magnitude, electrically measured in picocoulombs, 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 angular range. For larger angular separation, the acoustic amplitudes are uncorrelated and not anticorrelated. Some physical aspects of streamers in oil are illuminated by this observation and some theoretical considerations. The streamer velocity may, for example, be estimated