Long-term and Short-term AC Treeing Breakdown of Epoxy/Micro-Silica/Nano-Silicate Composite in Needle-Plate Electrodes

In order to characterize insulation properties of epoxy/micro-silica/nano-silicate composite (EMNC), long-termand short-term AC treeing tests were carried out undr non-uniform electric field generated between needle-plateelectrodes. In a long-term test, a 10 kV (60 Hz) electrical field was applied to the specimen positioned between theelectrodes with a distance of 2.7 mm in an insulating oil bath at 30℃, and a typical branch type electrical tree wasobserved in the neat epoxy resin and breakdown took place at 1,042 min after applying the 10 kVelectrical field.Meanwhile, the spherical tree with the tree length of 237 μm was seen in EMNC-65-0.3 at 52,380 min (36.4 day) andthen the test was stopped because the tree propagation rate was too low. In the short-term test, an electrial field wasapplied to a 3.5 mm-thick specimen at an increasing voltage rate of 0.5 kV/s until breakdown in insulating oil bathat 30℃ and 130℃, and the data was estimated by Weibull statistical analysis. The electrical insulation breakdownstrength for neat epoxy resin was 1,763 kV/mm at 30℃, while that for EMNC-65-0.3 was 2,604 kV/mm, which was amodified value of 47%. As was expected, the breakdown strength decreased at higher test temperatures.