Enhanced Dielectric
Breakdown Property of Polypropylene
Based on Mesoscopic Structure Modulation by Crystal Phase Transformation
for High Voltage Power Cable Insulation
posted on 2024-02-28, 07:15authored byYou Wu, Zhonglei Li, Heyu Wang, Zhong Zheng, Boxue Du
As an environmentally friendly polymer material, isotactic
polypropylene
(pp), possesses excellent dielectric properties while it can be recycled,
so it is regarded as having promising application prospects in the
field of high voltage power cable insulation. However, the increasing
operating voltage rating also puts higher demands on its insulation
reliability. In this study, an intrinsic modulation method for pp
insulation based on mesoscopic structure modulation by crystal phase
transformation is proposed, which not only effectively improved the
dielectric properties but also enhanced the mechanical toughness synergistically.
The transformation of the crystal phase from the α-crystal to
β-crystal within the PP/β-NA samples was successfully
achieved by the solution blending method. The crystallization efficiency
is greatly promoted, and the crystal structure is further improved
at the same time. As the proportion of β-crystal gradually increases,
the elongation at break could be raised to 451% at maximum. The difference
in dielectric parameters between the crystal and amorphous regions
is caused by the variation in the molecular chain density and arrangement,
which is also the main reason for further triggering the high-intensity
partial discharges and large-area electrical tree degradation in the
amorphous region between the spherocrystal boundary at the mesoscopic
scale. Compared with the premodification, the introduction of β-crystal
effectively alleviated the problem of electric field distortion. Among
them, the modified PP-β-0.2 sample had 16.8 kV/mm lower maximum
electric field, 2258 fewer total partial discharges, 420 μm2 less electrical tree cumulative damage area, and 28% higher
breakdown strength. Accordingly, it also has promising applications
in the manufacturing of high-voltage power cable insulation.