The Relation between Arc Resistance and Chemical Structure of Organic Insulating Materials

In view of the fact that synthetic resin is extensively used as materials for making electric apparatuses and instruments, the important problem in this connection is about arc resistance, when arc takes place in that part of the apparatuses and instruments where the resin is used, or in those parts adjacent to such. Accordingly theoretical studies were made of initiation of arc with respect to chemical structure of insulating materials, and of the means of strengthening arc resistance by loading it with fillers from the standpoint of correlation between deteriorativity and molecular structure. In the theoretical studies the method used by D.J. Parr et al. to appreciate the tendency of tracking deterioration was adopted. It was thought that the tendency of carbonization or formation of organic semi-conductor was then expressed as the ratio of the sum of bond energies tending to produce carbon or organic semi-conductor to the total amount of energy in the molecule, ΔHc/ΔHs. According to this method arc resistance is found in experimental result to be nearly in proportion to ΔHc/ΔHs, the proportional constant standing in minus. It is to be noticed that the coefficient in correlation of arc resistance and ΔHc/ΔHs stood at -0.978. It is observed in this way that the assumption of possibility for arc resistance in resins in their chemical structure is justified to a certain degree. It is to be added that for measurement of arc resistance ASTM D 495-61 standard test method was adopted, and that for test materials such thermosetting resin and thermoplastic resin were used, as phenol resin, epoxy resin, polyester resin, polyvinyl chloride, etc. It is shown also, and is mechanically proved in the light of correlation between deteriorativity and molecular structure, that synthetic resin can be used to advantage by reinforcing it by loading it with fillers, to promote its arc resistance about three times as strong. It is not whatever kind of resin, however, that has property of arc resistance that can be strengthened by loading it with diluent fillers, no matter in what large quantity.