Research On Grounded DC Tree Inhibition Method In XLPE Insulation Materials

Cross-linked polyethylene?XLPE?is the first-choice material for the high voltage DC power cable insulation.To improve the DC insulation properties of XLPE is the key for the independent research and development of high voltage DC cable materials in our country.When the cable core suffers a short circuit instantaneously,grounded DC tree phenomenon will occur in DC cable insulation layer,which is a threat to the safe operation of the cable.Therefore,to inhibit the grounded DC tree through modification of material is of great significance to further improve the voltage level of XLPE insulation for high-voltage DC cable,but also meaningful to promote the domestic manufacture of high voltage DC cable materials.In order to obtain modification methods which can effectively inhibit the electrical tree in XLPE material,the voltage stabilizer modified XLPE was prepared firstly,the influences of voltage stabilizer on the resistance to grounded DC tree of XLPE at different voltages and different temperatures were tested by taking commercial DC cable material and pure XLPE as references.The results show that the initiation rate and growth rate of grounded DC tree increase with the test voltage.Adding voltage stabilizer can obviously improve the performance of inhibiting grounded DC tree of the material at room temperature,and inhibit the initiation and growth of grounded DC tree.Its effect is similar to the commercial XLPE cable material.With the increase of the content of voltage stabilizer,the resistance of grounded DC tree increases.Under 30?,50?and 70?,the resistance of grounded DC tree of XLPE material are all the worst.Under 30?,the electrical tree inhibition ability of the commercial cable material is better than that of voltage stabilizer modified materials.Under 50?,their effects are almost equal.Under 70?,the electrical tree inhibition ability of voltage stabilizer modified material is significantly better than that of the commercial cable material.The higher the temperature is,the more obvious the effect of voltage stabilizer on the resistance of grounded DC tree of XLPE is.In addition,the effects of 1wt%nano-SiO₂ doping on the resistance to AC electrical tree and grounded DC tree as well as AC and DC breakdown strength of XLPE were also studied.The experimental results show that with the increase of test voltage,the grounded DC tree in XLPE,nano-modified XLPE and commercial cable materials all become easier to initiate and propagation,and the inhibition effect of nano-modified XLPE composite on the growth of grounded DC tree increases with the test voltage.Under power frequency AC voltage,the AC breakdown strength and AC electrical tree initiation voltage of nanocomposite are higher than those of XLPE.However,the inhibition of AC electrical tree growth by the nano-SiO₂ modified composite are merely limited in the early stage of electrical tree growth.After the tree reach a certain length,its electrical tree grows at a faster rate than XLPE.In this study,it was confirmed that the addition of voltage stabilizer and nano-SiO₂ can effectively improve the resistance of XLPE to the grounded DC tree,and the inhibition effect of nano-SiO₂ modification on grounded DC tree is better than that on AC electrical tree.