New insulation material boosts HVDC cable performance
Researchers from Chalmers University of Technology, University of Bologna, Lund University and Borealis AB found that adding a material usually used for flexible electronics to existing insulation could improve performance by a factor of three.
This allows more efficient high voltage DC (HVDC) cables that can be buried underground or laid on the seabed, allowing for considerable expansion of networks. Many projects are currently underway to connect different parts of the world. In Europe, for instance, the NordLink project will connect southern Norway and Germany, and HVDC cable projects form a significant part of Germany’s energy plans
“For us to handle the rapidly increasing global demand for electricity, efficient and safe HVDC cables are an essential component. The supply of renewable energy can fluctuate, so being able to transport electricity through long distance networks is a necessity for ensuring a steady and reliable distribution,” saod Christian Müller, leader of the research and Professor at the Department of Chemistry and Chemical Engineering at Chalmers University of Technology.
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One way to reduce transmission losses is by increasing the direct current voltage level, but this puts more pressure on the insulation. “An increase in the transmission voltage adversely affects the insulation of an HVDC cable,” said Xiangdong Xu, research specialist at Chalmers. “The resulting higher electric field stresses could be handled if the electrical conductivity of the insulation material was reduced sufficiently.”
The basis of the new material is polyethylene, which is already used for insulation in existing HVDC cables. Now, by adding very small amounts – 5 parts per million – of the conjugated polymer known as poly(3-hexylthiophene), the researchers were able to lower the electrical conductivity by up to three times.
The additive, also known as P3HT, is a widely studied material for flexible and printed electronics. However, this is the first time they have been used and tested as an additive to modify the properties of a commodity plastic. The manufacture of a 100 km long HVDC cable with a 6 cm wide conducting core surrounded by a 3 cm thick insulation layer would require about 4 kg of P3HT, which would in due time considerably boost the availability of the conjugated polymer.
Given the tiny amounts required, this opens up new possibilities for manufacturers. Other possible substances that have previously been used to reduce the conductivity are nanoparticles of various metal oxides and other polyolefins, but these require significantly higher quantities. Repurposing conjugated polymers as an additive for cable insulation, rather than employing them as the active material in optoelectronic devices, may considerably enhance the use of the material.
“In materials science, we strive to use additives in as small quantities as possible, in order to increase the potential for them to be used in industry and for better recycling potential. The fact that only a very small amount of this additive is required to achieve the effect is a big advantage,” said Müller. “Our hope is that this study can really open up a new field of research, inspiring other researchers to look into designing and optimising plastics with advanced electrical properties for energy transport and storage applications,” he said.
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