T&D World Magazine

Program on Technology Innovation: A Superconducting DC Cable

Shortly after the beginning of the 20th century, DC power transmission was replaced by AC in order to achieve efficient transmission of electric power over long distances with available conductors and at safe distribution voltages. However, DC power was not completely abandoned, and the advent of solid-state power electronic AC-to-DC conversion equipment has reinvigorated its application. High-voltage DC power is more desirable for long-range transmission than AC in many ways: DC uses two wires rather than three, uses a simpler conductor, eliminates capacitive elements to cancel inherent inductive behavior, and can use the earth as one of the currentcarrying elements. When justified by a lower cost per kilometer, DC transmission is now used for long-distance, high-power transmission lines as well as for interconnecting asynchronous ac systems.

This report describes the design of an interregional, superconducting DC cable system that is intended to achieve 10 GW power capacity with a nominal current and voltage of 100 kA and 100 kV. When installed, it will enhance the safety, reliability, and efficiency of the existing AC power grid and enable a level of bulk power transfer that is not conceivable with today’s conventional technology. Superconducting DC cable systems are inherently suitable for long-distance, high-power, bulk energy transfer without the disadvantages of either high-voltage DC or extrahigh-voltage AC systems. The superconducting DC cable is projected to have greater reliability and security, substantially lower losses, a smaller right-of-way footprint, fewer siting restrictions, and the ability to be terminated at distribution voltages in or near load centers. An underground superconducting DC cable system could transport many gigawatts of power from remote energy farms (wind, hydropower, coal, or nuclear facilities) to urban load centers with minimal impact on the environment. The superconducting DC cable will serve multiple, distributed generators and loads, using voltage source converter–based technology for the power on and off ramps....

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