Research On The Effects Of Voltage Stabilizers On The Insulation Properties Of EPDM And Their Mechanisms

High-voltage cable accessories are limited by the particularity of the materials and structure,there is a multi-layer structure at the connection with the cable,which is easy to distort the electric field,accelerate aging of the insulation,and even cause insulation breakdown in severe cases.In-depth research on the electrical resistance of ethylene propylene diene monomer(EPDM)insulation materials will help promote the development of high-voltage cable accessories.In order to obtain EPDM insulation materials with excellent electrical properties,four voltage stabilizers were selected to modify EPDM such as dibenzylideneacetone(RBBT)、2’-Hydroxychalcone(RQCT)、 4-propenoxy-2-hydroxybenzophenone(AOHBP)、2-propenyl-4,6-bibenzoylresorcinol(ADR).The effects of four voltage stabilizers on EPDM’s AC electrical tree resistance performance,AC and DC breakdown strength were systematically studied.The results shows that all four voltage stabilizers can increase the initial voltage of the EPDM’s AC electrical tree,change the EPDM electrical tree morphology from a mixed shape to a clump,and inhibit the growth of the electrical tree;Among the four voltage stabilizers,Only when the addition amount of voltage stabilizers RBBT and AOHBP is 0.25 phr,it have a positive effect on the improvement of the AC breakdown strength of EPDM;All four voltage stabilizers can effectively improve the DC breakdown strength of EPDM.In order to explore the anti-migration properties of the four voltage stabilizers and the long-term effectiveness of improving the DC breakdown strength of EPDM,the four modified EPDM samples with the highest DC breakdown strength among various voltage stabilizers are selected and placed in a vacuum drying oven at 80°C for vacuum heat treatment for 100 days,the DC breakdown strength and dielectric spectra of the materias before and after degassing have been compared.The results show that the four voltage stabilizers can further improve the DC breakdown strength of EPDM,and the dispersibility of data is also less than the date of pure EPDM material,which proves that the voltage stabilizers has excellent anti-migration properties and the long-term effectiveness of improving the DC breakdown strength of EPDM;the introduction of voltage stabilizer into EPDM will increase the relative permittivity and dielectric loss tangent,the relative permittivity and the dielectric loss tangent of the sample after vacuum heat treatment further increases.Infrared spectrum analysis have verified that all four voltage stabilizers may be grafted to EPDM macromolecules through radical addition reaction during the cross-linking process,ensureing that they can exist stably in EPDM,exhibiting anti-migration properties and long-term of the voltage stabilizers.The heat flow curve of the EPDM cross-linking process was tested by differential scanning calorimetry(DSC),and it was found that the reaction enthalpy change of the modified material added with four voltage stabilizers was significantly higher than that of EPDM,indicating that the four voltage stabilizers can participate in and intensify the cross-linking reactiion process of EPDM.In order to explore the influence of voltage stabilizer on the DC breakdown strength under pressure and surface breakdown voltage,pressure device and surface breakdown device were designed.The DC breakdown experiment under pressure shows that the DC breakdown strength of EPDM first increase and than decreases with the increase of pressure,and the DC breakdown strength of the modified EPDM material with voltage stabilizer decreases;The results of surface breakdown experiment shows that the four voltage stabilizers has a certain positive effect on the improvement of surface breakdown voltage,and the improvement of the breakdown voltage of the EPDM/XLPE double-layer dielectric interface is more significant.