Testing of three high temperature superconducting power cables installed at Detroit Edison's Frisbie substation in a joint industry-government demonstration project has led to the conclusion that only one of the 400 foot cables is suitable for energising. First commercial testing will probably not now take place before the end of the year.
Pirelli reported in July to the DOE Peer Review on Superconductivity that it had completed its analysis of the HTS cables following the discovery in January, during cooling of the cables prior to energising and beginning tests, that the cable was leaking. The breach, a so-called vacuum leak, turned out to be in the cryostat, the thermal insulation system, although the exact cause is as yet unknown.
Subsequent testing of the cryostat has persuaded manufacturer and project co-sponsor Pirelli that only one of the cables should be energised. The other two cables are to be replaced with six copper cables, a new liquid nitrogen return path will be installed, and system tests will be conducted using the third cable. Pirelli considers that this will accomplish almost completely the performance evaluation of the superconducting components as that expected from three-cable tests.
Pirelli could nonetheless report some success from its experience to date on this pioneering project, the first installation of an underground HTS cable in a US utility network. The cable packaging test has produced information considered to be equal in importance to the superconductivity test itself, and the American Superconductor HTS wires exceeded their performance specifications.
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