Research On The Propagation Mechanism And Inhibition Method Of Electrical Tree In Silicone Rubber

Silicone rubber has been widely used in high-voltage cross-linked polyethylene（XLPE） power cables as stress cone and main insulation of prefabricated attachmentsfor its excellent thermal, mechanical and insulation properties. The existence of stressconcentration is inevitable in the cable attachments due to its complicated structure,and defects will be produced or introduced during the process of production andinstallation. All these factors mentioned above will accelerate the deterioration ofsilicone rubber in long-term running, and causing the appearance of electrical tree,which eventually leads to insulation failure. Therefore, the research on thephenomenon of electrical tree in silicone rubber has a very important theoretical andpractical value.The phenomenon of electrical tree in silicon rubber is investigated by using thetypical needle-plate electrode, both pure and nano-structured silicone rubberspecimens were prepared to study the effect of ambient temperature, power frequency,and SiO₂nano particles on the treeing characteristics. Combined with the molecularstructure and physical properties of silicone rubber, the action mechanism of eachfactor is explained. Main conclusions are as follows:The influence of ambient temperature on the treeing characteristics in roomtemperature vulcanizing silicone rubber was studied. It is found that all the electricaltrees in silicon rubber are white dendritic channel. There are four typical electricaltree structures, namely branch-like, bush-like, pine-like and bush-pine mixed. Theappearance probability of different structures is obviously affected by the ambienttemperature, in which the proportion of bush-like tree increases with ambienttemperature gradually. The initiation time of the electrical tree increases with theambient temperature, while the cumulative probability of treeing breakdowndecreases with it.A variable frequency power supply was employed to study the influence ofpower frequency on the characteristics of electrical tree in silicone rubber. Obtainedresults show that a new structure bine-like tree appears at high frequencies （≥2kHz）,its growth rate is greater than other types. The initiation time decreases with theincrease of power frequency, and the average fractal dimension of dominant structure at each frequency, which varies in the range of1.2¹.8, shows a linear increasingtrend with the increase of frequency. The cumulative breakdown probability increaseswith frequency, which is related to the increase of frequency of bothelectro-mechanical stress nearby the tip and the discharge in tree channel.In order to investigate the inhibition mechanism of SiO₂nanoparticles onelectrical tree in silicon rubber, specimens with different quality of SiO₂particles isprepared. With the increase content of nanoparticles, the cumulative initiationprobability within the same applying time decrease obviously, and the width of branchchannel also reduce with it. In the range of0to3%, the number of branch channels,the average fractal dimension both increase with the nanoparticle content, accordingly,the cumulative breakdown probability decrease with it. Nano-SiO₂particles canimprove the trap depth of silicone rubber, thus inhibiting the injection of the electronsfrom the needle electrode, the interaction with the Si-O bond will increase theelasticity modulus of silicone rubber, moreover, the resistance performance todischarge of nanoparticles also plays an important role in obstructing the developmentof electrical trees, all the above reasons have relation to the inhibitory effect on theelectrical tree in nano-structured silicon rubber.