The electrical characteristics of dc superconducting cables of two power ratings were studied: 3 GW and 500 MW. Two designs were considered for each of the two power ratings. In the first design, the SUPPLY stream of the cryogen is surrounded by the high-voltage high-temperature superconductor cylinder. The RETURN stream of the cryogen is on the grounded side of the system. In the second design, both the SUPPLY and the RETURN streams of the cryogen are on the grounded side of the cable. Two electrical characteristics of these cables were studied: 1) fault currents and 2) current harmonics. It was concluded that neither the fault currents nor the current harmonics pose any problems in the operation of the dc superconducting cables.

http://www.w2agz.com/Library/Superconductivity/Cable%20Archives/09-15-05%20Chowdhuri,%20et%20al,%20paper1rev6.pdf

Feasibility of electric power transmission by DC superconducting cables

Silver-sheathed multifilamentary BiPbSrCaCuO 2223 superconducting wires with long length and high Jc of over 10 4 A/cm 2 (77.3K, OT) were developed by using the powder-in-tube method. A scaling law, which can be adopted in a wide temperature and magnetic field range, was found. Using this scaling law, we can estimate Jc at any temperature and magnetic field by using the wire performance at 77K without external field. Low AC loss wires and high strength wires were also developed for future applications. High electrical resistivity of the matrix and the use of twisted filaments are effective for reducing the AC losses. Good stress and strain tolerant characteristics were obtained for silver alloy sheathed wires. As a result of the progress in wire technology, we were able to fabricate many application prototypes. In high amperage conductor applications, current leads, bus bars and cable conductors were developed. In magnet applications, pancake magnets cooled by a GM refrigerator and solid nitrogen, as well as a layer wound magnet for high magnetic field NMR application at 4.2K, were developed.

Development of Ag-sheathed Bi2223 superconducting wires and their applications

In recent decades, extensive research has been conducted on the electrification of commercial aircraft to reduce the dependence on mechanical, hydraulic, and pneumatic systems and replace them with electrical systems. A primary goal of this path is to make the power density of the more-/all-electric aircraft (MEA/AEA) closer to that of conventional aircraft. While current commercial aircraft operate at voltages below 1 kV, it is widely accepted that higher operating voltage is necessary for MEA/AEA. NASA has envisaged a voltage level of at least 6 kV for MEA. In the language of electrical insulation technology, higher voltage levels translate into higher electric tension on the insulation system. A serious challenge stems from the fact that, at high altitudes, high-voltage insulation design strategies are not necessarily as efficient as at sea level due to differences in environmental conditions, including lower pressure, higher moisture level, microgravity, and plasma radiation. In this article, challenges associated with the electrical insulation design of future aircraft are reviewed. These challenges extend to almost any part of the electric power system in an aircraft, such as electric machines, power converters, cables, and printed circuit boards (PCBs). An overview of the aging factors, such as internal discharges, arc tracking, and thermal degradation, is accompanied by a discussion of the potential of novel insulating material and the ways to reinforce the current commercial dielectric materials. Finally, considerations for testing at simulated high-altitude conditions and the existing standards and their deficits are investigated.

Insulation Materials and Systems for More- and All-Electric Aircraft: A Review Identifying Challenges and Future Research Needs

Studies on developing an HTS (High-Temperature Superconducting) power cable with high transmission capacity and less loss are actively being performed worldwide. In Korea, an HTS power cable is being developed which applies cold dielectric type that a cable core wrapped by insulating papers is impregnated in liquid nitrogen. The insulating paper used in cold dielectric type is LPP (Laminated Polypropylene Paper) which has less dielectric loss and a superior dielectric property. In this paper, AC and lightning impulse breakdown strength and V-t characteristics with mini-model cables which were manufactured as the same structure with an HTS power cable were researched. Also, a thickness of insulation layer for a 154 kV class HTS power cable was designed as a result.

A Study on Insulation Characteristics of Laminated Polypropylene Paper for an HTS Cable

The 500-m high temperature superconducting (HTS) cable has been constructed in the Yokosuka area, CRIEPI, by CRIEPI, The Furukawa Electric Co. and Super-GM. Its design voltage is 77 kV and the thickness of the electrical insulation layer should be 8 mm made of semi-synthetic paper (polypropylene laminated paper). During cooling, the capacitance and dielectric loss tangent were measured periodically. After cooling, which means that the HTS cable was fully filled with liquid nitrogen (LN/sub 2/), the initial voltage withstand test was carried out. This paper describes the design method of the electrical insulation layer including determination of the testing voltage and the result of the initial voltage withstand test, and the permittivity calculated from the capacitance, and dielectric loss tangent.

Dielectric properties of 500 m long HTS power cable

For the optimization of electrical insulation design for high temperature superconducting (HTS) cable, evaluation of electrical insulation characteristics especially for butt gap of LN/sub 2/ impregnated cold dielectric (CD) which consists of the wrapped tape insulation impregnated with LN/sub 2/ plays an important role. This paper presents partial discharge (PD) inception and breakdown characteristics in LN/sub 2/ impregnated butt gap model which modeled a weak point of the wrapped tape insulation impregnated with LN/sub 2/ and cable model with short length with polypropylene laminated paper (PPLP/sup /spl reg//), Nomex/sup /spl reg// paper and cellulose paper. PD current pulse was found to have a steep rise time of /spl sim/ ns and amplitude of /spl sim/ tens /spl mu/A at PD inception voltage region. Little dependency of breakdown stress on the insulating material is found. PD inception stress is almost independent of insulation thickness of 1 to 3 mm. The requirement insulation thickness for 66 kV class HTS cable is estimated to be /spl sim/ 5 mm under PD-free condition from viewpoint of long-term reliability.

T. Takahashi

Papers

Electrical insulation characteristics of cold dielectric high temperature superconducting cable