Abstract
Space charges tend to accumulate on the surface and at the interface of ethylene–propylene–diene terpolymer (EPDM), serving as high voltage direct current (HVDC) cable accessory insulation, which likely induces electrical field distortion and dielectric breakdown. Direct fluorination is an effective method to modify the surface characteristics of the EPDM without altering the bulk properties too much. In this paper, the surface morphology, hydrophobic properties, relative permittivity, and DC conductivity of the EPDM before and after fluorination treatment were tested. Furthermore, the surface and interface charge behaviors in the HVDC cable accessory were investigated by the pulsed electroacoustic (PEA) method, and explained from the point of view of trap distribution. The results show that fluorination helps the EPDM polymer obtain lower surface energy and relative permittivity, which is beneficial to the interface match in composite insulation systems. The lowest degree of space charge accumulation occurs in EPDM with 30 min of fluorination. After analyzing the results of the 3D potentials and the density of states (DOS) behaviors in EPDM before and after fluorination, it can be found that fluorination treatment introduces shallower electron traps, and the special electrostatic potential after fluorination can significantly suppress the space charge accumulation at the interface in the HVDC cable accessory.
Highlights
Polymer dielectrics are always preferred in the high voltage direct current (HVDC) power cable insulation system, considering their excellent mechanical and electrical properties [1,2,3]
Results show that the fluorine element content in the red frame of the surface layer increases with the treatment time for both the ethylene–propylene–diene terpolymer (EPDM) and low density polyethylene (LDPE)
scanning electron microscope (SEM) and EDAX results have proven that fluorinated EPDM samples have a surface layer containing fluorine atoms which are formed on the smoother surface
Summary
Polymer dielectrics are always preferred in the HVDC power cable insulation system, considering their excellent mechanical and electrical properties [1,2,3]. Space charges are inclined to accumulate at the interface in the composite insulation system consisting of different dielectrics, like the HVDC cable accessory, which will distort the partial electrical field, cause discharge along the interface, and induce dielectric breakdown in the HVDC cable system [5,6]. Vu et al considered that the interface charge was produced by the Maxwell–Wagner polarization in the bilayer insulation [7]. A theoretical model that includes the multi-factors of interface charge behaviors and methods for their effective suppression are urgently needed to support the reliability and safety of the HVDC cable accessory There have been many papers reporting that the surface state and interface barrier have strong correlation with the accumulation of the interface charge [8,9].
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