抄録
A study on arc resistance of insulating materials at low temperatures is considered important in the insulation design of various electric apparatus, especially at terminal parts of electric apparatus, where cryogenic temperature liquid is used as the electric insulating material.
In this paper, the arc resistance tests of synthetic resins at low temperatures were carried out in air and in liquid nitrogen and the effect of low temperature on arc resistance was investigated. The low temperature effect on the process of arc deteriorations were also discussed.
As the test method, ASTM D495 standard test method was followed closely. Since the firing potential becomes high in air at low temperatures, the applied voltage was fixed at 28kV. In liquid nitrogen, it was fixed at 45kV, because the firing potential is still higher.
It was found that the arc resistance generally increased in air at low temperatures compared with that at room temperature. In liquid nitrogen, however, there were two cases; the one with increasing arc resistance and the other with decreasing arc resistance.
When the temperature was changed from low temperatures to room temperature in the air, the change of arc resistance showed different patterns, such as a slowly decreasing curve with temperature or an abruptly decreasing curve, depending upon the species of resins. The carbonization did not take place in liquid nitrogen in Epoxy-unfilled, phenolic paper-filled, PVC resin, etc. but the erosion took place in those resins, indicating the change in form of arc deterioration.
When the electrodes were placed not on the same plane of sample but on the upper and side surface of polyester-glass laminate, Melamine-glass laminate and Silicone-glass laminate in liquid nitrogen, the arc resistance decreased occasionally by the dielectric breakdown of the specimen which took place at the tip and the other part of upper electrode.
