High voltage insulation materials based on functional polymer nanocomposites – compounding, structure, stability

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Project abstract

The objective of this project was to establish relationships between processing parameters, nanoparticle dispersion and breakdown strength in LDPE nanocomposites and to investigate whether carbon-based filler materials can be used in field grading materials for use in HVDC cable accessories.

A general tendency has been that insulation systems in high voltage equipment become exposed to higher electric, thermal, mechanical and environmental stresses. Nanostructured polymeric materials provide a great number of opportunities in this context thanks to their high specific interfacial area, which can be used to utilize for trapping charge carriers as well as serving as scattering sites for hot electrons preceding electrical breakdown. It is important to study the influence of nanoparticle dispersion on the dielectric properties. This was done on nanocomposites of the extruded HVDC material LDPE. The effect of processing temperature, screw rotation velocity and processing time on particle dispersion and breakdown strength was assessed. It was shown that nanocomposites could be obtained that were essentially free of agglomerates. Furthermore, it was shown that nanocomposites that contained smaller agglomerates (< 3 µm) had no negative impact of the agglomerates, whereas composites with larger agglomerates showed a moderate depression in breakdown strength (maximum by 16 %). Silicone rubber filled with 3 wt.% graphene oxide exhibited a non-liunear resistivity when exposed to an increasing DC field. It is believed that the percolated structured of the lamellar shaped filler particles was responsible for this performance. The resistivity decreased gradually from 10¹⁴ to 10¹¹ ohm m as the electric field increased from 0.2 to 6 kV/mm. The resistivity could be tailored by reducing the graphene oxide (i.e. by removing oxygen from the filler). Polymer composites filled with reduced graphene oxide have potential applications as field grading materials in HVDC cable accessories.

Summary of work

A homogenous dispersion of metal oxide nanoparticles in polyolefin's (EBA or PE) using a mini-extruder has been achieved. Various ways to define particle dispersion have been tested. Influence of processing parameters on particle dispersion has then been evaluated using multivariate analysis. The influence of dispersion on electric breakdown test has been investigated. Graphene oxide filled silicone rubber samples have been prepared and electrical characterized, e.g. resistivity measurements, dielectric measurements. The long term stability is also studied.

2015. A silicone rubber filled with low amounts (3 wt.%) of Graphene Oxide has been prepared which exhibits similar non-linear resistivity as a commercial field grading material for HVDC applications.

Event log

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Project reference-group

Professor Ulf W. Gedde,  KTH Fibre and Polymer Technology
Adjunct Prof. Henrik Hillborg,  ABB Cooperate Research

Publications by this researcher

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Structure and Electrical Properties of Silicone Rubber Filled with Thermally Reduced Graphene Oxide
Wangshu Li,   Ulf W. Gedde,   Henrik Hillborg.
2016,   IEEE transactions on dielectrics and electrical insulation, vol. 23(2)

LDPE/AI203 Nanocomposites and Reduced Graphene Oxide Filled PDMS used as Insulating and Electric Field Grading Materials in HVDC Cable Systems
Wangshu Li.
2015,   Thesis (Licentiate), KTH Royal Institute of Technology, TRITA-CHE-Report 2015:30

Influence of Process Conditions and Particle Dispersion on the AC Breakdown Strength of Polyethylene-aluminium Oxide Nanocomposites
Wangshu Li,   Henrik Hillborg,   Ulf W. Gedde.
2015,   IEEE transactions on dielectrics and electrical insulation, vol. 22(6)

Publication list last updated from DiVA on 2024-08-22 22:58.

Page started: 2012-11-01
Last generated: 2024-08-22