Shrinkback Phenomenon in High-Temperature Medium-Voltage Cables With Fluorinated Ethylene Propylene Insulation

The article describes the problem of insulation shrinkback in cables with fluorinated ethylene propylene (FEP) insulation. The shrinkback effect occurs when the insulating material is subjected to an increased temperature and then cooled down to ambient temperature. This effect has been widely described for standard cross-linked polyethylene (XLPE) insulation; however, it was not tested for FEP cables, which are designed to be operated at much higher temperatures than XLPE ones. The article describes the experiment in which various cable samples were exposed to cycling thermal tests with different test temperatures, cooling time, and number of cycles. It was found that the shrinkback effect occurs in all groups and cable sizes above 90 °C and it increased at higher temperatures. Cables with FEP insulation can operate at temperatures up to 200 °C, and therefore this effect will have a direct impact on all cable terminations that are prepared at ambient temperature. The solution to reduce the effect is to preheat the cable to a higher temperature than its intended operation temperature. A single heating cycle can remove approximately 50% of the relaxation phenomenon. The novelty of this work lies in the study of medium- and high-voltage (MV/HV) cables with FEP insulation, shedding light on the shrinkback effect and its implications for cable performance and reliability.