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Reduction of flexible cable vibrations has been one of the key engineering focuses for magnetic disk drives to meet subnanometer recording precision requirement. Common approach to reduce the vibrations is to adopt additional polyimide-like damping layer on underlying homogeneous flexible cable, adding in homogeneity long the cable's dynamic loop. This paper investigates the effect of inhomogeneous composition along the cable's dynamic loop on the cable's vibration modes. The cable's profiles are obtained by experimental image processing and used in the proposed finite element model. It is found that placement and design of the inhomogeneous composition such as the damping layer for passive vibration control or piezoelectric layer for active vibration control can significantly alter the cable's modal responses, which potentially can be used to reduce transmission of the cable's vibrations onto the rotary actuator.

The first tests of a superconducting power cable within the power grid of a public utility were conducted at the Steweag power plant in Arnstein, Austria, in 1979. The cable (conceived by Klaudy [1],[2] and manufactured by ATF and Kabelmetal) is 50 m long and consists of seven concentric, longitudinally welded corrugated tubes using the "Wellmantel" technology. The fully flexible cable was shipped on a reel by conventional rail and road transportation means. It was easily installed by technicians familiar with conventional cable laying methods. No problem developed during the evacuation and cooling by liquid helium to about 6.5 K. The shield was cooled by liquid nitrogen to about 77 K. The cable was designed for 110 kV and 1.6 kA. Although transmitting the entire available power output of the station, the full rating of the cable was not attained during the tests. The conductor for these first trials was made of copper-stabilized niobium. The tests were concluded without any problems and all components performed in accordance with their design expectations under actual field conditions.

Following an extensive study of cryogenic power transmission systems under development in this country and abroad it was concluded at Brookhaven that a flexible superconducting ac cable appeared to be the best choice for an economical high-capacity underground system with superior technical characteristics. A form of niobium-tin has been developed for this application with an intrinsic low-loss performance at 60 Hz. In addition, it has been determined that the ac characteristics of many commercial forms of Nb 3 Sn are degraded by additives, these effects are described. A flexible cable will require a lapped plastic insulation which must possess necessary properties both at room temperature and at the operating temperature, these are listed together with a summary of test results. Several designs for the cryogenic envelope to contain the cable are under development, the design options and trade-offs are discussed. Using performance data based on present knowledge of helium-cooled cables, systems were designed for an actual utility company transmission corridor 43 miles long rated at 4800 MVA. These designs are costed and compared to conventional transmission facilities.

To demonstrate the technical feasibility and capability of superconducting ac cables a 35 m long ac single phase test cable for 110 kV and 10 kA is under construction at present. The rigid cryogenic envelope has already been assembled. Good experience was gained with the applied mounting technique which is described. Wires consisting of a high purity Al-core enclosed by a thin layer of Nb are used as cable conductors. They were fabricated in lengths of several thousand meters under large scale conditions and exhibited excellent electrical behaviour. After manufacturing some dummies with pure Al-wires, a 50 m long originally sized flexible cable core consisting of superconducting wires and wrapped HDPE tape insulation was fabricated on conventional cable machinery in our cable works. Dielectric measurements at 4.2 K and 2.5 bar on originally sized and large scale fabricated cable core pieces yielded breakdown voltages, partial discharge inception voltages and dissipation factors which are compatible with cable standards. Two one phase 110 kV - 10 kA cable terminations have been constructed and tested. They showed satisfying behaviour with respect to stress and current loads.