Simultaneous Effect of Thermal Aging and Phase Separation on Insulation Properties of 500-kV DC XLPE Blends With Voltage Stabilizers

Thermal aging degrades the insulating layer and shortens the service life of the power cable. In this article, pure XLPE and four XLPE/voltage stabilizer samples were prepared using 500-kV dc XLPE raw pellets and aged at 135 °C for 168 h. Various mechanical and electrical tests were performed to characterize the insulation properties of the samples. The results show that after aging, the mechanical and breakdown strengths of all the samples decrease, the conductivity increases, and the space charge accumulation increases. Besides, the aging process also makes the modification effect of the voltage stabilizers on the XLPE no longer obvious. The trap characteristics indicate that the deep energy level traps cause space charge accumulation and electric field distortion, which decreases the insulation performance of all the samples. The molecular dynamic simulation illustrates that the phase separation of the XLPE and the voltage stabilizers leads to the uneven dispersion of the voltage stabilizers, which will form the weak point of insulation and lead to the failure of the voltage stabilizers.