HVDC Cable Accessory Insulation

Introduction

HVDC cables have shown great advantages as they combine features of the lower energy losses with the same current, lower line costs, unique practical feasibility and the transmission capability for long-distance, high-power underground or underwater transmission. Polymer insulated HVDC cables have demonstrated many advantages as they combine traits of the material and the transmission capability for long-distance, high-power underground or underwater transmission (Y. Zhou et al.,2015; M. Marzinotto and G. Mazzanti,2015; G. Chen et al.,2015; W. Long and S. Nilsson,2007). The performance of cable accessories, as an essential part of the HVDC networks, is of great concern to the reliability of the system, due to the electrical, thermal and mechanical designs of these structures coupled with high risks in environmental pollution and installs errors. However, under high DC electric stress, it is likely to accumulate charges at the interface of materials with different conductivity and permittivity, which will lead to accelerated degradation of insulation systems under various stress conditions, particularly after polarity reversal, leading to material degradation and possibly premature failure (S. Delpino et al.,2008; B. X. Du et al.,2016; M. L. Fu et al.,2008). The interface charge behavior and its impact become much more unpredictable considering the complex geometry, doping of fillers, etc.

Ethylene-propylene-diene Terpolymer (EPDM) composites are used extensively in the cable accessories and provide a better performance compared to traditional materials, which can reduce the physical size of HVDC cable components and the production costs. Besides, EVA composites are also used in the cable accessories for making heat shrinkable insulation, semi-conductive insulation jackets and cable accessory insulation, due to its ability to accept high filler proportions without embrittlement or loss of mechanical integrity, and the ease of crosslinking. Cable accessories can be made by incorporation of specific conductive additives, nonlinear resistive fillers, etc. (L. Donzel et al.,2011; I. Tamayo et al.,2011; L. Gao et al.,2016), which are used in cable accessories to uniform electric field and prevent interface flashover or breakdown. However, the cable accessories have to confront the problem of interface charge accumulation.