Power transmission by submarine cable plays an important role in the construction of cross-sea network.The basic characteristics of the semi-conductive shielding material and the electrical as well as thermal properties of the semi-conductive layer/insulating layer directly affect the overall insulation performance of the cable.In the paper

the physical and chemical properties of semi-conductive shielding material for submarine cables are characterized from the basic physical and chemical properties of the semi-conductive material

and the thermal properties and breakdown characteristics of the semi-conductive layer/insulating layer are studied.The thermal conductivity coefficient analysis shows that the thermal conductivity coefficient of the semi-conductive layer of submarine cable

due to a large of CB particle

is high and is about twice that of the insulation layer.With the increase of temperature

the thermal conductivity coefficient for both of them shows gradual increase trend.The thermal conductivity coefficient of the semi-conductive layer increases from 0.68 W/（m·K） at 25℃to 0.83 W/（m·K） at 80℃.The thermal expansion characteristic analysis shows that with the increase of temperature

the thermal expansion coefficient of the insulation layer of the submarine cable is about 1.5 times higher than that of the semi-conductive layer.Generally

the deformation of above two kinds of materials is not significant due to influence of temperature and the relative deformation is 2.47%and 1.28%at 90℃respectively.The breakdown test of the submarine cable shows that with the increase of temperature

the breakdown field strength of insulation layer of submarine cable decreases gradually from 125.2 kV/mm at 25℃down to 92.5 kV/mm at 90℃.Compared to the insulation layer

the breakdown field strength drop of semi conductive layer/insulation composite structure is not evident

indicating that both of them have good compatibility and maintain excellent breakdown performance in high temperature in particular.This work has important reference significance for the insulation performance improvement of submarine cable and the analysis of breakdown fault.