Enhanced High-Temperature DC Dielectric Performance of Crosslinked Polyethylene with a Polystyrene Pinning Structure

Abstract

In this paper, we propose a method on improving direct current (DC) dielectric performance by designing a polystyrene (PS) pinning crosslinked polyethylene (XLPE) for the application of insulation materials on high voltage direct current (HVDC) extruded cable. Electrical experimental results show that the addition of PS (1–5 phr, parts per hundreds of resin) can significantly reduce DC conductivity and increase DC breakdown strength of XLPE in the test temperature range of 30–90 °C. Microstructure investigation shows PS distributed as particles could participate in the formation of a crosslinking network with the help of a crosslinking agent, thus forming a polymer pinning structure at the interface between XLPE and PS. It is believed that such a special design strengthens the structure of XLPE, which leads to the improved DC dielectric performance at elevated temperatures. Our findings may contribute a new solution for developing HVDC cable insulation materials.

Crosslinking Dependence of Direct Current Breakdown Performance for XLPE-PS Composites at Different Temperatures

“…Bulges in the matrix caused by fracture disappear or cannot be distinguished in crosslinked samples, which reveals that crosslinking process enhances the interactions between that molecular chains for polyethylene. Instead of cavities in LDPE/PS as shown in Figure 5 b, PS particles in XLPE-PS 3# crack along the cross section, which has been ascribed to the crosslinking between PS and polyethylene [ 10 ].…”

“…In the amorphous area, there exist impurities, crosslinking points and cavities. Due to the incompatibility of PS and polyethylene, PS would be located in the amorphous area [ 10 ]. The role of dispersed PS particles in XLPE-PS composites may be embodied in two aspects.…”

“…Firstly, pellets of LDPE and PS as well as antioxidant were mixed using a twin-screw extruder at 170 °C with a rotation speed of 60 r/min in which only 1 part per hundred of resin (phr) of PS was employed [ 10 ]. Then a series of DCP contents including 0.8, 1, 1.3 and 2 phr were added into pellets of the blends by soaking at 70 °C for 24 h. Finally, samples with different dimensions were obtained by hot-pressing.…”

“…To develop polyethylene-based materials with more stable DC breakdown behaviors, our previous study proposed a method of deliberately introducing polystyrene (PS) to enhance the high-temperature DC dielectric performance of XLPE and it is considered that the enhancement of DC dielectric performance may mainly rely on the formation of pinning structures, in which the crosslinking process plays a vitally important role [ 10 ]. For pure XLPE, the crosslinking process can change the morphology, thus affecting the DC breakdown strength.…”

Dielectric Surface Flashover under Long-Term Repetitive Microsecond Pulses in Compressed Gas Environment

“…Conventionally, for a dielectric/gas composite insulation system between a couple of parallel-plane electrodes, insulation failures are mostly caused by surface flashover instead of bulk breakdown, since the interface is always the weakest part under RMPs. In previous investigations, factors affecting surface flashover, mainly in gas-insulated switchgears (GISs), were systematically studied [ 3 , 4 , 5 ] and various methods have been developed to improve bulk and surface insulation strengths under AC and DC conditions [ 6 , 7 , 8 ]. When it comes to pulsed flashovers, the physical processes and mechanisms of solid-vacuum surface flashovers have been discussed in detail in pulsed power systems [ 9 , 10 ].…”