Improving the DC Dielectric Properties of XLPE with Appropriate Content of Dicumyl Peroxide for HVDC Cables Insulation

In this research, crosslinked polyethylene (XLPE) is developed with selective content of dicumyl peroxide (DCP), and the influence of microstructural properties and chemical composition on the mechanical and direct current (DC) dielectric properties are investigated. The measurements for the microstructural analysis are taken by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), gel content test and Fourier transform infrared (FTIR). The mechanical properties of XLPE are evaluated by hot-set test. The results of microstructural and chemical composition show that the increase in DCP content increases the crosslinking degree from 74.3% to 81.6%, reduces the crystallinity/lamella thickness from 36.8% to 35.5%/7.6-7.1 nm, reduces the average molecular weight between two crosslinks by 0.01 kg/mol and reduces the oxidation level/carbonyl index. The increase in DCP in XLPE samples decreases the permanent elongation from 2.2% to 0% and elongation rate from 300% to 80% of the cable insulation. The rise in DCP content increases the crosslinking degree due to which the DC resistivity and activation energy is increased. The DC breakdown strength at 30-90 degrees C is increased due to the increase in crosslinking degree and reduction in carbonyl index/oxidation level. The space charge accumulation is measured at 30 degrees C under 20-60 kV/mm, resulting in less homo-charges and hetero-charges with the increase in DCP. It is proven that the role of appropriate DCP content is vital in increasing the DC dielectric performance, internal material characteristics and mechanical performance of XLPE.

Automated summary

In this research, crosslinked polyethylene (XLPE) with selective content of dicumyl peroxide (DCP) was developed, and the influence of microstructural properties and chemical composition on the mechanical and direct current (DC) dielectric properties were investigated. The results showed that the increase in DCP content increased the crosslinking degree, reduced the crystallinity/lamella thickness, average molecular weight between two crosslinks, and oxidation level/carbonyl index. The increase in DCP in XLPE samples decreased the permanent elongation and elongation rate. The rise in DCP content increased the crosslinking degree which improved the DC resistivity and activation energy, and increased the DC breakdown strength. The space charge accumulation measurement showed that the increase in DCP reduced the homo-charges and hetero-charges. It was proven that the appropriate DCP content played a vital role in enhancing the DC dielectric performance, internal material characteristics, and mechanical performance of XLPE.