Synthesis of a novel semi-conductive composites doping with La_0.8Sr_0.2MnO₃ for excellent electric performance for HVDC cable

The semi-conductive layer located between the wire core and the insulation layer in high voltage direct current (HVDC) cable plays a vital role in uniform electric field and affecting space charges behaviors. In this work, the research idea of adding ionic conductive particles to semi-conductive materials to improve the conductive network and reduce the energy of the moving charge inside it and to suppress charge injection was proposed. Semi-conductive composites doped with different La_0.8Sr_0.2MnO₃ (LSM) contents were prepared. Resistivity at different temperatures was measured to investigate the positive temperature coe°Cient (PTC) effect. Pulse electro-acoustic (PEA) method and thermal-stimulation depolarization currents (TSDC) tests of the insulation layers were carried out. From the results, space charge distribution and TSDC currents in the insulation samples were analyzed to evaluate the inhibitory effect on space charge injection. When LSM content is 6 wt. %, the experimental results show that the PTC effect of the specimen and charge injection are both being suppressed significantly. The maximum resistivity of it is decreased by 53.3% and the insulation sample has the smallest charge amount, 1.85 x 10^-7 C under 10 kV/mm-decreased by 40%, 3.6 x 10^-7 C under 20 kV/mm-decreased by 45%, and 6.42 x 10^-7 C under 30 kV/mm-decreased by 26%. When the LSM content reaches 10 wt. %, the suppression effect on the PTC effect and the charge injection are both weakened, owing to the agglomeration of the conductive particles inside the composites which leads to the interface electric field distortion and results in charge injection enhancement.