The Effect of Geometrical Forms of Samples on Arc Resistance of Electrical Insulating Materials

Abstract

It is generally considered that the materials for electrical insulation get their arc resistance differently effected according to the kinds of the insulating materials and to their respective nature. The differentiation in the effective resistance of the materials is due also to the geometrical forms of the samples. It is considered that the latter give rise to somewhat divergent processes and forms of deterioration, and so affect the arc resistance of the electrical insulation materials considerably. The experiments were carried out accordingly about the effect of the geometrical forms of the samples on their arc resistance. To the experiments was adapted the method of ASTM D 495-61. Since it was required that the samples of insulating materials were to be of various forms, such materials as epoxy resin and polyester resin were preferred for the experiments as fit for being cast readily into required shapes. The following results were obtained from these experiments.(1) Considerable effect was given by the geometrical forms of the samples on the arc resistance of the insulating materials. The arc resistance in the case of columnar samples of from 10 to 15mm in diameter showed its drop to from 84 to 90%, even to from 60 to 68% of the arc resistance in the case of plates. Then there is larger rate of drop of arc resistance in the case of epoxy resin than that in the case of polyester resin.(2) No obvious effect to save the drop of arc resistance due to variation in diameter in the case of columnar samples was seen by reinforcing the fillers with such materials as CaCO3, SiO2, TiO2, mica and talcum.(3) The same effect of the forms of the samples on the arc resistance of the electrical insulating materials is observed in conic samples as in those columnar.(4) When the columnar samples had pleats and trenches, no obvious effect to save the drop of arc resistance due to variation in diameter in the case of columnar samples was seen, so long as the variation in the diameter due to the presence of the pleat or the trench is about from 0.55 to 1.30 times as large as that of the columnar samples without pleat or trench.