Study On Electrical Tree Growth Characteristics Of Polypropylene/Elastomer Blends Under AC Voltage

Polymer materials are widely used in high-voltage cable insulation materials,because of their low cost,high breakdown strength,low dielectric constant,low dielectric loss,et al.Polypropylene(PP)has excellent electrical properties and recyclability,which is in line with the future development trend of power cable insulation and is expected to be a substitute for cross-linked polyethylene(XLPE).Electrical tree is the most common electrical aging phenomenon in polymers.It is generally considered to be precursors to the breakdown of insulation,which seriously threatens the safe operation of power systems.Therefore,it is necessary to target the growth characteristics of electrical tree in polymers.The purpose of this work is to investigate the electrical treeing behaviour in toughened PP,and discuss the effects of temperature and trap distribution on the growth characteristics of electric tree in PP/elastomer blends.The specific work is as follows,Two elastomers(propylene-based elastomer PBE and octene ethylene elastomer POE)were used to toughen the isotactic polypropylene(iPP).The physical and chemical properties and electrical properties of the blends under different elastomer contents were investigated,and the effects of elastomer content and type on the electrical treeing behaviour were studied.The results showed that as the elastomer content increases from 0% to 30%,the compatibility of the elastomer and the iPP matrix deteriorates,and the crystallinity of the blend decreases.The addition of the elastomer reduces the insulation properties of the blends,such as an increase in relative dielectric constant and a decrease in volume resistivity and breakdown strength.In addition,the resistance to electrical tree of the PP/elastomer blend decreases with the increases of elastomer content.Since the compatibility of PBE and iPP matrix is better than that of POE and iPP matrix,the growth rate of electrical tree in PP/PBE blends is relatively low.The effect of temperature on the growth characteristics of electrical tree was investigated by controlling the experimental temperature,and the correlation between trap distribution characteristics and electric treeing behaviour was discussed.The results showed that the effect of temperature on the growth rate of tree shows a non-monotonic change.As the temperature increases from 20? to 60?,the growth rate of the electrical tree increases with the increase of the elastomer content;as the temperature reaches 80?,the shape of the electrical tree changes from branch to pine,and the growth rate becomes slow;as the temperature is 100?,the growth rate continuously increases.In addition,the growth rate of the electrical tree shows a significant dependence on the trap level.The shallow trap helps to increase the growth rate of the electrical tree,and the deep trap can inhibit the growth of the electrical tree.The higher the trap level of PP/elastomer blends is,the stronger its resistance to electrical tree is.