Light emission study in transformer oil and along oil/cellulose interface using a spark-gap system

Interfaces between oil and oil-impregnated-pressboard are known to weaken insulation system strength. The work here describes differences in the observed discharges in transformer oils and along oil/oil-impregnated-pressboard interfaces. Oil breakdown in a uniform electric field was initiated by triggering a spark gap either at the anode or at the cathode using a liquid trigatron. Light emission during the breakdown processes was detected using a photomultiplier tube. Breakdown voltage, time to breakdown, streamer propagation speed and polarity effect were seen to differ in a transformer oil and along an oil/oil-impregnated pressboard interface.