Effect of Electrical Aging On PPLP Insulation Characteristics in LN2

The high-temperature superconductivity (HTS) DC cable has brought huge economic benefits and has been widely used in the system with its low line loss. The Polypropylene laminated paper (PPLP) tape is wrapped around the core due to its excellent insulation properties, which produces butt gaps. Since cables in HTS DC transmission system often withstand DC and AC composite voltage, these gaps make partial discharge (PD) easier to occur. Meanwhile, degradation occurs in PPLP under long-term electrical stress, which could threaten the safe operation of the power system. Therefore, this article conducted an electrical aging test in liquid nitrogen (LN
₂
) to simulate the actual operating environment of PPLP, and also measured the conductivity, relative permittivity, PD, and breakdown strength of PPLP with different aging times in LN
₂
. The results show that the conductivity basically increases with the increase of aging time and relative permittivity has a significant increase at the end of the aging stage. As the aging time increases, the PD activity of PPLP becomes more intense and the DC breakdown strength shows a downward trend. The reason for the deterioration of PPLP insulation performance after aging was analyzed. Besides, the effect of different alternating components on PD was studied in the case of constant effective voltage. When the alternating component decreases, the number of PD is significantly reduced.