Site: ABB Corporate Research U.S. Contact: ABB-TTI Baden-Daetwil 1021 Main Campus Drive Switzerland Raleigh, NC 27607 Date Visited: 13 June 1996 WTEC Attendees: R.D. Blaugher (report author), D. Larbalestier Hosts: Ove Albertsson, Manager, Department of Power Engineering, Vasteras, Sweden Willi Paul, Head of Applied Physics Group, Baden-Daetwil Harry Zueger, Research and Development Engineer, Transformers, ABB Secheron, Ltd. Jacob Rhyner, Computer Engineering Department, Baden-Daetwil
The ABB Group was formed in 1988, primarily from the merger of Asea (Sweden) and Brown-Boveri (Switzerland). ABB now operates a number of "independent" business units throughout the world, principally in Switzerland, Sweden, Germany, and the United States, engaged in the research, development, and manufacture of a wide range of electric-power-related components (e.g., switchgear, transformers, generators, overhead and underground transmission cables, and power conditioning for motors and transmission system stability). As a result of the promising business outlook for superconducting electric power components, the ABB group has supported R&D on superconductivity for many years in both LTS and HTS. Past research primarily focused on energy storage (SMES), SC generators, transformers, and fault-current limiters. Even though ABB is a major supplier of both overhead and underground transmission cables, it has not pursued SC transmission. ABB previously studied both dc and ac SC transmission and concluded that their economics combined with their refrigeration requirements made them unattractive.
ABB is following SC cable development and would consider future efforts in this area, dependent on progress in its current programs. Energy storage, strongly followed by ABB in the past, is considered an important area. At the time of the WTEC team's visit, ABB had been developing a major SMES system for the Swiss railroad, but this was terminated due to the realization of an alternate, less costly, solution. ABB has no current plans for storage but will continue to evaluate the technology. The support for superconductivity technology within ABB is fairly strong and represents support from upper management from both the research side and the business units. ABB will continue to support R&D on SC technology to provide "core" capability within the research and business units in the event that commercialization of SC power devices is demonstrated to be feasible. In that regard, the WTEC team's hosts at ABB indicated that the company's eventual commercialization of HTS power devices will be completely dependent on the realization of a satisfactory HTS conductor with acceptable performance and cost.
ABB's major research effort at the time of the team's visit was focused on development of HTS transformers and fault-current limiters, with essentially equivalent interest devoted to these two activities. ABB had considered SC transformers for some time and earlier had constructed an LTS prototype for evaluation and for developing practical experience. This early effort encouraged pursuit of the program directed at eventual development of a mid-range 100 MVA (220 kV/15 kV) transformer using HTS windings and operating at 77 K with liquid nitrogen. ABB researchers feel that realization of HTS transformers at 100 MVA, which is typical for Switzerland, would show a significant reduction in weight (approximately 50%) and electrical losses (approximately 70%) and offer a marked capital cost advantage of nearly 20% over conventional transformers. The ABB approach assumes realization of an HTS conductor with Je = 104 A/cm2 at 0.1-0.2 T and specific ac losses of 0.25 mW/Am. ABB is currently working on a joint project to demonstrate a 630 kVA, three-phase transformer with HTS windings. This joint effort involves ABB Baden-Daetwil, the ABB Secheron transformer facility located in Geneva, Switzerland, Electricité de France, SIG (the electrical utility for Geneva, Switzerland), the Swiss Federal Office of Energy (BEW), the Swiss Electric Association (VSE, PSEL), other Swiss utilities (CREE), and also American Superconductor Corp. (U.S.), which is supplying the HTS conductor. Table ABB.1 presents the design specifications for the 630 kVA transformer.
HTS Transformer Specifications
The other major program underway at ABB-Daetwil is directed at use of HTS materials for demonstration of a fault-current limiter. The ABB interest in superconducting fault-current limiters (SCFCL) is driven by the high mechanical and thermal stresses imposed on the switchgear and transformers due to short-circuit (Isc) transient conditions on interconnected electrical systems. The objective is to reduce these stresses, proportional to Isc2, to a level where the fault current doesn't exceed 10 times the normal current. The SCFCL should have these primary features:
ABB has built and tested several prototypes of an SCFCL based on a design referred to as the "shielded iron core concept." The ABB device consists of a warm iron core, which under normal operation is shielded by a superconducting cylinder enclosed in a fiberglass liquid-nitrogen-cooled Dewar. A normal conducting (Cu) coil, connected in series with the line, is wound external to the Dewar/SC cylinder. Under normal operation the SC cylinder isolates, i.e., "shields," the copper coil from the inner Fe, resulting in a low impedance, similar to an air-core reactor. Under fault conditions, the field induced in the copper coil is sufficient to "normalize" the SC cylinder, allowing flux penetration, thus linking the Fe core to the copper coil with a resultant increase in impedance and an immediate lowering of the fault current. ABB constructed and tested a 100 kW prototype using a stack of four Bi-2212 rings, 8 cm long, 20 cm diameter, wall thickness d = 1.8 mm, that were individually melt-processed in a rotating Ag mold. The total height of the stack was 35 cm. Tests were conducted at 480 V with fault-currents of 8 kA at different phase angles of the source voltage. For the two extreme phase angle conditions at peak source voltage and at zero source voltage, the fault current was limited to a peak value of ~900 A or ~5x the normal current. ABB researchers feel the shielded core device can be scaled to MVA values, which would allow test and possible installation in electric systems with high faults and low operating currents, e.g., in the excitation, auxiliary, and startup branches of power stations. A new ABB three-phase 1.2 MW FCL is now in operation in a power station in Löntsch, Switzerland.