The electrical properties and processing characteristic of the cross-linked polyethylene based insulation for high-voltage direct current cables

The doping of nanofillers is considered to be an effective method to effectively suppress the space charge of the cross-linked polyethylene (XLPE) insulating materials used for high-voltage direct current (HVDC) cables. For the large cross section of HVDC cables, the very high cleanliness standard of the XLPE materials is demanded. During the extrusion process of cables, the XLPE insulation is usually filtered the impurities by passing through one precision filter with more than 500 meshes for a long time. Besides, the long-term processing stability of insulating materials is of great importance. Therefore, the nanofillers need to be uniformly dispersed when they are added into the polyethylene (LDPE) matrix, ensuring that no agglomeration and impurities are introduced. In our research, the nano-sized aluminum oxide (Al
₂
O
₃
) particles are selected and dispersed in the LDPE matrix to prepare the master-batches. The Al
₂
O
₃
modified XLPE insulating materials for HVDC cables was prepared by melting blending the pure LDPE and the achieved the master-batches after the crosslinking process. The dispersion characteristics of Al
₂
O
₃
were investigated using the scanning electron microscope (SEM) and single-screw extruder. It was found that the nano-Al
₂
O
₃
, modified XLPE materials indicated stable processing properties. Their torsion variation was almost the same as that of pure XLPE through the filter screen with 500 meshes during extrusion process. Besides, their space charge distribution behavior was investigated by pulsed electro-acoustic (PEA) technique. The results show that the addition of Al
₂
O
₃
could effectively inhibit the generation and accumulation of space charge.