Changes of thermoplastic PE cable insulation properties caused by the overload current

Experiments were conducted to determine structural changes (degree of crystallinity) of PE (polyethylene), the development of treeing (velocity, shape), and changes of tan delta and breakdown strength as a result of thermal aging. The results show that thermal aging causes increased separation of spherulites. Overheating leads to the appearance of amorphous regions with dimensions exceeding the diameter of the neighboring spherulites. It is shown that the treeing channels develop faster in amorphous thermoplastic PE insulation than in a partially crystalline one and that tan delta increases, but the breakdown decreases with the time of thermal aging.>