Study on the breakdown characteristics of flowing insulating oil

The inner environment of a power transformer depends on the operating condition and the atmosphere of the installation area. Even though the static characteristics of insulating oil are well known, there are many factors which make it very difficult to predict the physical and electrical characteristics of transformer oil in real operating conditions. One of these, the breakdown characteristics of insulating oil in the static condition would be changed by flow speed in the duct, temperature and streaming electrification. The authors have charged insulating oil and circulated it with different velocity and temperature. And then they tested the breakdown strength for each different condition. First, they measured the breakdown voltage of non-charged insulating oil and then they compared it with the breakdown voltage of charged oil. The breakdown voltage of insulating oil that was charged was lower than that of non-charged oil. The temperature and velocity effect on the breakdown voltage were more complex when the insulating oil was charged. Also the breakdown voltage decreased with the increase of charged particles by the applied DC electric field and it was dependent of oil temperature and velocity.