Nexans has completed successfully the test of the world's first high-voltage direct-current (HVDC) high-temperature superconductor (HTS) power transmission cable designed for 200 kV. This result constitutes an important step in demonstrating the capability of underground HVDC HTS cables to transfer bulk power at the gigawatt levels required by proposed supergrid projects, such as the Tres Amigas renewable energy market hub in the United States.

The voltage tests were performed at the Nexans high-voltage laboratory in Hanover, Germany. A prototype HVDC HTS cable together with a termination was subjected to a series of tests according to CIGRÉ test recommendations. They included testing at a voltage of 360 kV, representing 1.8 times the 200-kV operating voltage, during several hours. In addition, the system was successfully submitted to superimposed overvoltages such as the ones occurring during lightning or switching events.

The HVDC HTS cable is based on a similar configuration to the 138-kV ac HTS cable currently operating in Long Island, New York, U.S. The key design challenges addressed by Nexans have concerned the termination (connecting the cable to the electrical network), which is completely different from that used in ac systems.

The next step is for Nexans to adapt this HTS cable system to the very high currents (up to 12,500 A) required to transfer several gigawatts of power in order to take full advantage of the low-loss power transmission capabilities of HTS cables. Nexans also will develop suitable joints to enable the installation of long lengths of HTS cable as well as for repairs.

The Tres Amigas project would create the first renewable energy market hub in the United States to enable faster adoption of renewable energy and increase the reliability of the U.S. grid. For the first time, the project in Clovis, New Mexico, would unite the three U.S. power grids — the Eastern Interconnection, the Western Interconnection and the Texas Interconnection.

The three grids would be connected by Superconducting Electricity Pipelines, comprising HVDC power cables and voltage source converter ac/dc power converters. The Tres Amigas renewable energy market hub would be a 9.6-km (6-mile) triangular electricity circuit capable of transferring and balancing many gigawatts of renewable power between the grids.

HVDC HTS cables contained in underground pipelines would transfer gigawatts of power with nearly 100% efficiency between each of the hub's three converter stations. HTS cables are more efficient than other transmission options, and they offer a significantly greater power density, so that more power can be transferred within a smaller footprint on the ground.

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