PP/PP-HI/silica nanocomposites for HVDC cable insulation: Are silica clusters beneficial for space charge accumulation?

Xiaozhen He,Ilkka Rytöluoto,Paolo Seri,Rafal Anyszka,Amirhossein Mahtabani,Hadi Naderiallaf,Minna Niittymäki,Eetta Saarimäki,Christelle Mazel,Gabriele Perego,Kari Lahti,Mika Paajanen,Wilma Dierkes,Anke Blume

doi:10.1016/j.polymertesting.2021.107186

Abstract

New potential High Voltage Direct Current (HVDC) cable insulation materials based on nanocomposites are developed in this study. The nanocomposites are produced by blending of polypropylene (PP), propylene-ethylene copolymer (PP–HI) and a modified fumed silica (A-silica) in a concentration of 1 and 2 wt %. The A-silica is successfully modified with (3-aminopropyl)triethoxysilane (APTES) via a solvent-free method, as proven by infrared spectroscopy, thermogravimetry and transmission electron microscope mapping.A-silica in the polymer matrix acts as a nucleating agent resulting in an increase of the crystallization temperature of the polymers and a smaller crystal size. Moreover, the silica addition modified the crystals morphology of the unfilled PP/PP-HI blend. The composite containing A-silica with 2 wt% contains bigger-size silica clusters than the composite filled with 1 wt%. The composite with the higher A-silica concentration shows lower space charge accumulation and a lower charge current value. Besides, much deeper traps and lower trap density are observed in the composite with 2 wt% A-silica addition compared to the one with a lower concentration. Surprisingly, the presence of silica clusters with dimensions of more than 200 nm exhibit a positive effect on reducing the space charge accumulation. However, the real cause of this improvement might be due to change of the electron distribution stemming from the amine-amine hydrogen bond formation, or the change of the chain mobility due to the presence of occluded polymer macromolecules constrained inside the high structure silica clusters. Both phenomena may lead to a higher energetic barrier of charge de-trapping, thus increasing the depth of the charge traps.

Highlights

The development of the High Voltage Direct Current (HVDC) tech nology did grow rapidly in the recent decades, owing to its lower cost and lower loss over long distance power transmission than High Voltage Alternating Current (HVAC) technology
One of the most promising approaches in the insulation material field is the development of dielectric nanocomposites, in which the electrical properties are tuned by addition of selected nano-sized fillers
The development of an HVDC insulation material based on PP/PP-HI/A-silica nanocomposites was presented

Summary

Introduction

The development of the High Voltage Direct Current (HVDC) tech nology did grow rapidly in the recent decades, owing to its lower cost and lower loss over long distance power transmission than High Voltage Alternating Current (HVAC) technology. This makes the HVDC profit able for integrating it in the remote renewable energy sources network such as wind or solar energy, and for efficiently transmitting electricity to the regions of demand. Most charge trapping sites are located at the interfacial zone, which has a significant influence on the charge-transport behavior and the space charge accumu lation of the nanocomposites [5]

Methods

Results

Conclusion