Sergio Spreafico

Long length manufacturing of high performance BSCCO-2223 tape for the Detroit Edison Power Cable Project

American Superconductor has manufactured the BSCCO-2223 tapes for the Detroit Edison Power Cable Project. Pirelli Cables and Systems, along with Detroit Edison, Lotepro, EPRI, and Los Alamos National Lab, are developing, manufacturing, and installing the worlds first HTS cable system in an electric utility network. Partially funded by the DOE-SPI program, the project goal is to fabricate, install, and test a 3-phase, 120-meter long, 100 MVA HTS cable system rated at 2400 A and 24 kV in Detroit Edisons Frisbie Station. Significant advances in HTS tape technology have been made in the past year, with average engineering critical current performance above 115 A at 77 K. We discuss the distribution of critical current as well as mechanical and environmental tests of more than 25 km of BSCCO tape manufactured for the Detroit Edison project. The environmental tests have been designed to simulate the behavior of HTS tapes under the actual operating conditions for an underground power cable.

Manufacturing and commissioning of 24 kV superconducting cable in Detroit

Abstract The development of power transmission system based on high temperature superconducting material is reaching an important goal with the ongoing Detroit Edison HTS Cable Project in Detroit, Michigan. AMSC, DOE, EPRI, LANL, Lotepro are the project partners. The system consist into designed 24 kV, 100 MVA three phase superconducting warm dielectric cables, compact terminations, one joint, refrigeration and control/monitoring system. Nine conventional cables in duct have been substituted with only three HTS cables operating at the same voltage and overall current. In this paper we present the status of the project.

Critical current versus field behaviour in Ag/BSCCO-2223 tapes with different critical currents

Abstract The dependence of J c upon applied magnetic field has been analysed in BSCCO-2223 tapes with different geometrical structures of the superconducting core. The samples, prepared by the PIT method, and rolled down to tapes of different thickness, were annealed up to three times with intermediate mechanical working. All measurements were carried out at 77 K, in magnetic field up to l T, applied both parallel and perpendicular with respect to the transport current. Several samples with the same J c and different I c and superconducting core thickness were measured and compared. All samples showed a qualitatively similar “memory effect”, with higher values of J c measured with decreasing magnetic field, but remarkable differences in the low fields regime, where thinner tapes (lower I c ) showed a faster decay of J c with B compared with the thicker ones. A simple semi-quantitative explanation, taking into account the self field of tapes, was well supported by tests carried out in a special experimental arrangement so designed as to allow to characterize the “true” zero self-field behaviour of the material.

Numerical modeling of a HTS cable

The finite element method has been employed in order to simulate the behavior of a HTS cable for transport current applications. The E-J model includes an anisotropic dependence of the critical current density J/sub c/ and power index n on the local magnetic field, whose magnitude is nonnegligible and determines the effective critical current of the cable. The cable consists of four electrically insulated layers, each of them composed by 20 superconducting tapes, providing a total critical current of about 4 kA. In order to obtain a uniform repartition of the current among the layers, a sufficiently high contact resistance has been inserted in the electric circuit. The ac losses and the field distribution have been computed. A comparison is also made with a simple electric model of a HTS cable.

Numerical analysis of the effects of the magnetic self-field on the transport properties of a multilayer HTS cable

In this paper, the effects of the magnetic self-field on the transport properties of a multilayer high-T/sub c/ superconducting (HTS) cable are investigated by means of two-dimensional finite-element method (FEM) simulations. Analyzed is a three-layer HTS cable, but the developed methods can be used for a different number of layers. The superconductor is described by the nonlinear power-law relation E=E/sub c/(J/J/sub c/)/sup n/, where the parameters J/sub c/ and n depend on the magnetic field experienced by the material. This dependence decreases the global transport capacity of the superconductor, enhancing its AC losses. It is shown that, especially at high transport currents, the AC losses are considerably higher than in the case where the dependence on the magnetic field is neglected. A simple electrical model, considering the cable from macroscopic point of view, has been proposed for finding the optimal winding pitches, leading to a uniform current repartition. The use of this electrical model allows to overcome the difficulties of direct three-dimensional FEM computations. In addition, the rapidity of solutions by the electric model gives the possibility of testing quickly many geometrical configurations in order to find the ones leading to an even current repartition. This optimization process would not be possible with detailed FEM simulations.

Measurement of DC critical current in superconducting cable with non-uniformities

We investigated the effect of nonuniform current distribution on the critical current experimentally determined on a superconducting cable. In theoretical model, the cable is considered as a set of parallel current paths, each containing one single tape. Critical currents, n-factors and contact resistances between each tape and current termination are the input data of the model. Spread in these parameters results in a nonuniform distribution of DC current among tapes. Then, the voltages on different tapes would vary, and the determination of cables critical current by a standard procedure becomes difficult. This was shown on a single-layer cable model, manufactured by placing 16 straight Bi-2223/Ag tapes in parallel on a cylindrical epoxy fiberglass mandrel. With the help of brass shunts connected in series with each tape, the currents in all the tapes can be measured simultaneously. Experimental signals registered on different tapes were in excellent agreement with theoretical predictions. We found the spread in contact resistances to be rather critical issue for our 1 m long model.

Status of warm dielectric cable installation at Detroit Edison

Abstract In response to the combined effects of growing energy demand and the impact of de-regulation of the electrical energy industry, pro-active utilities are ensuring flexibility and robustness of their networks, by upgrading or installed capacity in both transmission and distribution. In this regard, high-temperature superconducting (HTS) cable systems offer advantages where space, thermal capability and environmental conditions constrain capacity. To facilitate the transition of HTS cable technology from the laboratory to the field, Pirelli Cables and Systems, EPRI, Detroit Edison, a DTE Energy Company, ASC, and the US DOE have undertaken a program which will result in the demonstration of a HTS power cable to deliver electricity in a utility network. This program will demonstrate a retrofit upgrade application of the Warm Dielectric HTS cable design in the Detroit Edison utility network, and involve the design, engineering, installation, test and routine operation of a 24-kV, 100 MVA, 3-phase cable system. The original circuit, comprised of three parallel circuits of conventional cables, will be replaced by a single circuit of HTS cables which will provide the same power capacity. Each HTS cable will carry 2400 A RMS , a level triple the capacity of original cables powering this circuit. This paper addresses the issues relating to the field application of HTS cables in the context of the demonstration program.