high temperature superconductors

HIGH TEMPERATURE SUPERCONDUCTOR (HTS) CABLES AND
POWER INFRASTUCTURE REVOLUTION DREAMS IN INDIA

An ageing and inadequate power grid is now widely seen as among the greatest obstacles to efforts to restructure power markets in the India. In light of new and intensifying pressures on the nation’s power infrastructure, industry and policy leaders are looking to new technology solutions to increase the capacity and flexibility of the grid without further raising system voltages. High Temperature Superconductor (HTS) cable is regarded as one of the most promising new technologies to address these issues. Among HTS cable designs, one in particular – shielded cold dielectric cable – offers performance advantages particularly well suited to today’s siting, reliability and performance challenges.

Shielded cold dielectric HTS transmission cables feature very close spacing between the conductor and shield layers of wire in a coaxial cable. This close spacing results in several advantages: lower electrical losses; the virtual elimination of stray EMF; and significantly lower impedance than conventional cables and lines. Triaxial cables suited for distribution-voltage, high-current applications exhibit similar benefits. Of particular importance, the very low impedance (VLI) inherent in cables of coaxial or triaxial design makes it possible to control power flows over VLI circuits. These circuits inherently attract power flows, offloading adjacent, higher-impedance conventional circuits. Thus, for example, VLI superconductor cable (“VLI cable”) offers a means of “pulling” power away from heavily-loaded lines onto high-capacity pathways that flow directly into congested urban centers. This approach offers compelling advantages compared to the traditional strategy of “pushing” power into load centers using multiple, large overhead circuits with higher impedance ratings. In addition, variable impedance may be cost-effectively added to VLI circuits with relatively small, conventional phase angle regulators. Thus, VLI circuits can function like fully controllable DC circuits, but without the expense and complexity associated with AC-DC terminal stations.

The introduction of VLI cable enables new approaches to important challenges in grid
management. The strategic insertion of relatively short segments of VLI cable to bridge
bottlenecks can offload flows from overburdened conventional circuits, thereby expanding grid capacity, extending the useful life of conventional network elements, and raising overall asset utilization. Important economic, environmental and policy benefits include the following:
• VLI cable users will pay less to solve power flow problems with shorter lengths of cable, at lower voltage ratings, and with greater controllability. Siting options for new
generators will be expanded, and grid bottlenecks will be eased, improving overall power
system efficiency and lowering total system costs.
• Adoption of VLI cable will lead to enhanced system fuel efficiency and reduced air emissions, the elimination of stray EMF, and a much smaller physical footprint for grid
expansion projects, because VLI cable can be routed underground within a variety of
existing rights-of-way.
• Unobtrusive VLI cable offers a new way to achieve several important objectives. It can help to break the logjam over transmission siting; improve overall power system reliability; enhance power market competitiveness; attract merchant transmission investment; and advance environmental objectives.

Initial VLI superconductor cable projects now underway provide an opportunity to develop a reliability record and resolve system integration and other implementation issues. However, to speed the commercialization cycle for VLI cable, it is urgent to expand the range of demonstration projects and identify early commercial opportunities. With power markets in turmoil and transmission increasingly the center of attention, VLI cable is a breakthrough technology with great potential to solve many of the industry’s most pressing problems.