Effect of Nanoporous Molecular Sieves TS-1 on Electrical Properties of Crosslinked Polyethylene Nanocomposites

Abstract

Crosslinked polyethylene (XLPE) is an important polyethylene modification material which is widely used in high-voltage direct current (HVDC) transmission systems. Low-density polyethylene (LDPE) was used as a matrix to improve the thermal and electrical properties of XLPE composites through the synergistic effect of a crosslinking agent and nanopore structure molecular sieve, TS-1. It was found that the electrical and thermal properties of the matrices were different due to the crosslinking degree and crosslinking efficiency, and the introduction of TS-1 enhanced the dielectric constants of the two matrices to 2.53 and 2.54, and the direct current (DC) resistivities were increased to 3 × 10¹² and 4 × 10¹² Ω·m, with the enhancement of the thermal conductivity at different temperatures. As the applied voltage increases, the DC breakdown field strength is enhanced from 318 to 363 kV/mm and 330 to 356 kV/mm. The unique nanopore structure of TS-1 itself can inhibit the injection and accumulation in the internal space of crosslinked polyethylene composites, and the pore size effect of the filler can limit the development of electron impact ionization, inhibit the electron avalanche breakdown, and improve the strength of the external applied electric field (breakdown field) that TS-1/XLPE nanocomposites can withstand. This provides a new method for the preparation of nanocomposite insulating dielectric materials for HVDC transmission systems with better performance.

Keywords: aperture structure; breakdown field strength; crosslinked polyethylene composites; space charge; thermal conductivity.

Figure 1

Reaction mechanism diagram of LDPE with crosslinking additives. (a) BIPB and LDPE; (b) DCP and LDPE.

Figure 2

Schematic diagram of molecular structure changes during crosslinking process.

Figure 3

TEM images of TS-1 at different magnifications. (a) TEM image at a scale of 50 nm, (b) TEM image at a scale of 100 nm.

Figure 4

Cross-section SEM images of TS-1/XLPE-1 nanocomposites. (a) The 0.5 wt.% TS-1/XLPE-1 nanocomposite; (b) 1.0 wt.% TS-1/XLPE-1 nanocomposite; (c) 1.5 wt.% TS-1/XLPE-1 nanocomposite; (d) 2.0 wt.% TS-1/XLPE-1 nanocomposite; (e) 0.5 wt.% TS-1/XLPE-2 nanocomposites; (f) 1.0 wt.% TS-1/XLPE-2 nanocomposites; (g) 1.5 wt.% TS-1/XLPE-2 nanocomposites; (h) 2.0 wt.% TS-1/XLPE-2 nanocomposites.

Figure 5

Thermal conductivity TS-1/XLPE-1 and TS-1/XLPE-2 nanocomposites. (a) TS-1/XLPE-1 nanocomposites; (b) TS-1/XLPE-2 nanocomposites.

Figure 6

Line graph of thermal conductivity of TS-1/XLPE nanocomposites with filler content at different temperatures. (a) Thermal conductivity trend at 30 °C, (b) thermal conductivity trend at 50 °C, (c) thermal conductivity trend at 70 °C, (d) thermal conductivity trend at 90 °C.

Figure 7

Breakdown field diagrams of crosslinked polyethylene and LDPE prepared by adding different crosslinking additives. (a) Breakdown field strength of DCP/LDPE; (b) BIPB/LDPEDCP/LDPE.

Figure 8

Breakdown strength of TS-1/XLPE nanocomposites with different TS-1 concentrations, (a) TS-1/XLPE-1 nanocomposites, (b) XLPE-2 nanocomposites, (c) comparative histogram of breakdown field strength.

Figure 9

Schematic diagram of the mechanism of enhancement of breakdown field strength. (a) Schematic diagram of electron impact ionization conduction; (b) schematic diagram of the blocking effect of TS-1 on charge injection and transfer in XLPE matrix.

Figure 10

Volume resistivity of TS-1/XLPE nanocomposites with different TS-1 content.

Figure 11

Dielectric constant with frequency curves of XLPE/TS-1 nanocomposites. (a) XLPE-1/TS-1 nanocomposites; (b) XLPE-2/TS-1 nanocomposites; curves of dielectric loss versus frequency for XLPE/TS-1 nanocomposites. (c) XLPE-1/TS-1 nanocomposite; (d) XLPE-2/TS-1 nanocomposite.

Figure 12

The space charge density of XLPE and TS-1/XLPE nanocomposites: (a) XLPE-1, (b) XLPE-2, (c) XLPE-1/1.5 wt.% TS-1, (d) XLPE-2/1.5 wt.% TS-1.