Special Operational Requirements
McCall noted that HTS cable requires certain operational considerations that aren’t necessary with conventional cables. A utility will need to provide regular substation access to the cryo-cooling system supplier for periodic maintenance of the system. If fault current limiting HTS cable is used, the resulting alternate low-impedance/high-impedance characteristics of the cable may require more careful attention when setting up protective relay schemes. Conversely, an HTS cable requires no derating based on load levels, placement, or ambient temperature.
He emphasized that HTS cables can be used anywhere in the transmission grid. HTS cable systems consist of the cables, their terminations, and the cryo-cooling (refrigeration) system and its associated controls. In general, the cables should terminate in substations, as the cable terminations are larger than conventional terminations. The substation environment also needs to provide space for the required cryo-cooling equipment.
Cost Considerations
"The production cost of HTS wire is presently more expensive than that of copper, primarily due to the relatively small quantity of HTS wire currently being produced," McCall said. "The industry projects the latest HTS wire technology, referred to as 2G, will be no more expensive, and should ultimately be less expensive, than copper on a cost per kilo-amp-meter basis (price/performance ratio) once it enters large-scale production."
The cost of HTS cable systems must be considered in light of the overall solution they provide, he pointed out. For example, if a single cable can replace a bank of eight conventional cables, avoid extensive street work, and eliminate the need to upgrade dozens of circuit breakers, then that total benefit must be considered. As more HTS cables are installed and manufacturing capacity is scaled up, the cost of HTS wire, cooling systems, and so on will also drop, increasing the system’s economic value.
"Initial applications for HTS cables will be very high-value ones," he said. "HTS cables will initially be most cost competitive in urban, high-power, limited right-of-way applications. As manufacturing costs decrease, their financial competitiveness in a much wider variety of applications will grow as well, including the short- to medium-distance transmission applications where higher-voltage underground cables are currently deployed."
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