279 / 2022-03-15 00:06:03

Grafting Modification Improving Electric Treeing of Polypropylene and Its Mechanisms

Polypropylene cable,grafting modification,Electric tree,environmental friendly

Purpose/Aim

With the development of the civilization and industrialization, the severer demand of larger capacity and higher level of voltage transmission appear. As the shortage of land resource becomes more concerning nowadays, cables draw more attention. Although the traditional insulation of cables is Cross-linked Polyethylene whose electrical properties are outstanding, its weakness in thermal stability prevents it in enlarging the capacity of Cross-linked Polyethylene Cables. And what’s more, it can’t be recycled which is in the opposite direction to the environment policy. Polypropylene is considered to be one of the most possible materials to replace Cross-linked Polyethylene, as it shows great electrical properties and it has higher operating temperature when using as cable insulation and at the same time, it can be recycled when retired. Yet, to prevent the decrease of electrical properties of Polypropylene when improving its mechanical properties, the grafting modification is used in the study. And electrical treeing is one of the most dangerous phenomena before the breakdown of the insulation. Thus, studying the electrical treeing of grafting modified Polypropylene insulated cables in the radial direction is important to the development and application of Polypropylene cables.

Experimental/Modeling methods

Experimental samples of Polypropylene electrical treeing test were prepared by putting two needles vertically together with Polypropylene pellets. 2cm distance is kept between the needles. The pellets together with the needles were melting at 200℃ and 15MPa for 15min and then cooled to 20℃. After the samples were ready, one of the needles was grounded and the other one was operated as high voltage. The high voltage was output by a generator and an amplifier. The experiment temperature was 25℃ and the voltage was ±20kV and 50Hz.

Results/discussion

Grafting modification can significantly improve the electric tree properties of Polypropylene. TSDC results show that grafting modification can invite more deep traps which can limit the movement of space charge and thus making the inception of the electric trees in grafted Polypropylene difficult. DSC and SEM results show that the crystallinity of grafted Polypropylene better, which makes the growth of the trees slower.

Conclusions

The grafting modification can significantly improve the inception time of the tree in Polypropylene and it can stall the growing of the trees in grated polypropylene. The more monomers grafting to the Polypropylene, the more difficult for the trees to be incepted and the slower the trees to grow.

Appendix (Figure, table, image…)

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