Characterization of EPDM/micro-Silica/micro-Silicon Carbide (SiC)/nano-hBN Composites for HVDC Insulation
This study demonstrates that incorporating surface-modified nano-hBN into an EPDM/micro-SiC composite significantly enhances thermal conductivity and maximizes HVDC and HVAC breakdown strength, achieving peak electrical performance with a 20 phr nano-hBN loading.
Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer
High-voltage direct current power lines are the silent arteries of the modern grid, carrying massive amounts of electricity over vast distances with remarkable efficiency. Unlike the alternating current that powers most homes, which constantly reverses direction, direct current flows in a single, steady stream. This steady flow creates a unique challenge for the insulating materials that wrap around the cables: it causes invisible electrical charges to get stuck, or accumulate, within the material. Over time, these trapped charges distort the electric field, creating weak spots that can lead to catastrophic failure. To keep the grid running safely, engineers need insulators that can not only block electricity but also manage these trapped charges and shed the heat generated by the high-voltage current. The material of choice for many of these applications is a tough rubber called EPDM, known for its durability and resistance to weather, but on its own, it struggles to handle the intense heat and charge buildup of modern high-voltage systems.
Researchers at Joongbu University and the Hong Kong University of Science and Technology set out to improve this rubber by mixing it with two very different types of powder. They added microscopic grains of silicon carbide, a material that conducts electricity just enough to help spread out those trapped charges evenly, preventing them from clumping together. To tackle the heat problem, they introduced nano-sized particles of hexagonal boron nitride, a substance often called "white graphite" because its atoms are arranged in flat sheets similar to pencil lead, yet it acts as a perfect electrical insulator while conducting heat exceptionally well. The challenge was getting these tiny particles to mix evenly into the rubber without clumping, so the team chemically treated the surface of the particles to make them friendly to the rubber, then rolled the mixture together and baked it into a solid sheet.
The results of this mixing process were striking. When the researchers tested the new composite material, they found that adding the heat-conducting particles made a significant difference in how the material handled electrical stress. The best performance came when they added a specific amount of the nano-sized boron nitride—20 grams for every 100 grams of rubber. At this level, the material withstood direct current voltages up to 95.4 kilovolts per millimeter in a positive polarity test, a notable improvement over the unmodified rubber which failed at 87.3 kilovolts per millimeter. The improvement was even more pronounced in negative polarity tests, where the new material held up to 98.2 kilovolts per millimeter compared to the original 89.3. This suggests that the combination of the two powders creates a material that is better at both dispersing electrical charges and dissipating heat, two critical factors for preventing insulation failure.
Beyond electrical strength, the material showed a clear ability to move heat away from the source. As the researchers increased the amount of the heat-conducting boron nitride, the material's ability to transfer heat rose steadily. With the highest amount of boron nitride tested, the material conducted heat 1.55 times better than the rubber containing only the silicon carbide. This improved thermal performance is vital because it helps prevent the rubber from degrading under the high temperatures generated by the power lines. The material also maintained its physical strength; in fact, the tensile strength, or the force required to pull the material apart, increased slightly as more boron nitride was added, rising from 4.30 megapascals in the base mixture to 4.58 megapascals in the optimized blend. While the material became slightly less stretchy, it remained robust enough for practical use.
The study confirms that by carefully balancing the amount of these two additives, it is possible to create a superior insulating material for high-voltage direct current systems. The team found that adding too much of the nano-sized boron nitride actually reduced the electrical strength, indicating that there is a precise limit to how much can be added before the benefits diminish. The optimal mix, containing 20 grams of the nano-particles per 100 grams of rubber, emerged as the most effective formulation, offering a balanced improvement in electrical breakdown resistance, thermal management, and mechanical durability. This work provides a concrete path forward for developing insulation that can withstand the demanding conditions of future high-capacity power transmission networks.
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