Electrical Tree Propagation in XLPE Containing Untreated and Treated Silica Nanofiller

Electrical treeing is one of the main failure phenomena in cross-linked polyethylene (XLPE) cable insulation. Once the tree initiates in cable insulation, it starts to growth and finally leads to cable breakdown. To date, the silica nanofiller in XLPE was limited to the study of permittivity, dielectric loss, space charge, AC and impulse breakdown strength and partial discharge. The results from these cooperative tests show an improvement in dielectric and insulation properties over the pure XLPE cable insulation. However, the electrical tree properties in XLPE containing silica nanofiller are still uncertain. Therefore, this paper presents the investigation of electrical treeing propagation characteristic in XLPE with the inclusion of untreated and treated silica nanofiller. The silica nanofiller was treated with KH550. The concentration of untreated and treated silica nanofillers in XLPE was 0.5 wt%, 1.0 wt% and 1.5 wt%. The untreated and treated silica nanofillers has 96%-99% purity. The size of the untreated and treated nanofiller is within 20-30 nm and the shape is spherical. The test sample was prepared in rectangular slab with dimensions of 15mm x 25mm x 2mm. The XLPE and silica nanofiller was blended using Haake internal mixer and formed by hot press machine. The needle-plane electrodes were used and the gap between the needle tip and plane electrodes is 2mm. The electrical tree propagation was investigated by ramp up the applied voltage with the rate of 1 kV/sec until the electrical tree inception voltage (TIV) was observed. Then the applied voltage was kept constant at TIV for each sample to investigate the propagation of electrical tree growth. The electrical tree propagation and TIV in XLPE containing treated and untreated silica nanofillers were compared with the pure XLPE composite.