Space Charge And Conductivity Property Of Ultraviolet Cross Linked Polyethylene

It has been confirmed that UV cross-linked polyethylene has better waterproof tree-performance, lower partial discharge and higher production efficiency, which is suitable for large length of the submarine cable manufacturing. In order to ensure the efficiency of cross-linking, UV cross-linked polyethylene is often cross linked with linear low density polyethylene(LLDPE).This is due to that linear low density polyethylene has a higher degree of crystalline, and much more excellent electrical properties. In this essay, we are trying to research the feasibility about the UV cross as the DC-linked polyethylene cable insulation material.Linear low density polyethylene(LLDPE) has a higher degree of crystalline and breakdown strength, therefore in this essay,we can consider whether to replace LDPE using LLDPE as a DC current of the main insulation material or not.In order for comparison performance of space charge and conductivity properties using different polyethylene and further analyzing the effect by using different antioxidants, we use low-density polyethylene(LD200GH) and two kinds of linear low density polyethylene(LL3910AA, DFDA7042) as a base material with four different antioxidants(anti300, anti1010, anti1035, anti1076) in the experiment.Additionally, by UV-irradiation cross linking with LLDPE and LDPE carried peroxide chemical cross linking respectively to compare the performance of space charge distribution and conductivity properties and further analyze the reason. The conclusions are following:(1)The results of DSC and XRD show that the crystalline of LDPE,LLDPE7042 and LLDPE3910 is 34.48%, 36.39% and 51.82% respectively.Compared with LDPE, another two kinds of linear low density polyethylene having higher crystalline and melting temperature, whereas, LLDPE3910 has the highest crystalline with minimal electrical conductivity, and smaller change of conductivity with temperature increase, an anti-oxidant has nearly no effect on the performance ofelectrical conductivity. In conclusion, this phenomenon is due to the crystalline of LLDPE3910 reached 51.82%, which reduce free volume and make low carrier mobility.(2)Testing space charge showed that, the performance of space charge under LDPE and LLDPE7042 are different polarity charge, while there is no obvious space charge under LLDPE3910. At the same time, the experiment reveals that higher crystalline of LLDPE3910 inhibit directional migration of impurity ions in an electric field. The obvious phenomenon of space charge injection of LDPE is produced by adding antioxidants, which implied antioxidants promote the charge injection. For LLDPE3910, there are no obvious change for space charge after adding antioxidants. Because there is lack of long chain branching for LLDPE3910 molecule, narrower distribution of molecular weight, higher degree of internal structured lower defect density of electrode and material at the interface, which make lower injection of charge.(3) Experiment results of LLDPE3910 were UV radiation cross-linked by arranging two initiators and cross-linking agent in a groups show that space charge of different polarity of XL-LLDPE3910 BP using of small molecule initiators and crosslinking agent is much more than using of macromolecules initiator and cross-linking agent. The reason is that there is a large amount of cross-linking by-products during cross-linking, wherein cross-linking by products molecules are smaller and mobility are higher which are generated by cross linking small molecule initiator and a crosslinking agent. Cross-linked polyethylene has no obvious charge injection phenomenon by comparing with UV cross-linking of cross-linked polyethylene.This is due to that there is high crystalline for LLDPE3910 and high regularity of molecular chains segment.