Breakdown features in electric cables with polymeric insulation

Abstract

Compositions based on polyvinylchloride (PVC), which is sensitive to thermal aging, are used for the majority of electric cables as polymeric insulation. It is shown for the first time by the example of the most widespread polymeric insulation, which is made of polyvinylchloride preliminarily subjected to partial ther molysis, imitating its faster aging, that electrical conductivity of PVC can acquire an anomalous (not follow ing the Ohm law) character due to aging. Transitions of PVC from a state with usual (low) conductivity into a state with anomalously high conductivity that have a spontaneous uncontrollable character are observed in this case. It is especially noteworthy that the character of these variations is large scale, which makes it pos sible to easily transform PVC from the state of typical dielectric into the class of conductors. It is noted that the method of removal of a fire hazard (by maximally possible removal of short circuits caused by thermal aging of polymeric insulation) should have a preventive character, being the most efficient, simplest, and most convenient.

Principles of Thermal Degradation

“…189 This may cause deterioration of insulating properties in PVC due to its chemical decomposition. 190 Transition of PVC from a state with usual (low) conductivity into a state with anomalously high conductivity was observed. 189 Electrical conductivity of PVC can acquire an anomalous character due to aging.…”

“…189 The heat treatment above 150 o C degrades the breakdown properties of PVC cables working in temperatures from room temperature to 90 o C due to previous thermal decomposition accompanied by dehydrochlorination of PVC. 190 4.1.10 ADDITIVES Additives are always present in PVC to modify its properties. 190 Transition of PVC from a state with usual (low) conductivity into a state with anomalously high conductivity was observed.…”