R.C. Niemann

High-temperature superconducting current leads for micro-SMES application

SMES is being applied on a microscale (1-10 MJ stored energy) to improve electrical power quality. A major portion of the SMES refrigeration load is for cooling conventional (copper, vapor-cooled) current leads that transfer energy between the magnet and the power-conditioning equipment. The lead refrigeration load can be reduced significantly by the use of high-temperature superconductors (HTSs). An HTS current lead suitable for micro-SMES application has been designed. The lower stage of the lead employs HTSs. A transition between the lower stage and the conventional upper-stage lead is heat-intercepted by a cryocooler. Details of the design are presented. Construction and operating experiences are discussed. >

Design of a high-temperature superconductor current lead for electric utility SMES

Current leads that rely on high-temperature superconductors (HTSs) to deliver power to devices operating at liquid helium temperature have the potential to reduce refrigeration requirements to levels significantly below achievable with conventional leads. The design of HTS current leads suitable for use in near-term superconducting magnetic energy storage (SMES) is in progress. The SMES system has an 0.5 MWh energy capacity and a discharge power of 30 MW. Lead-design considerations include safety and reliability, electrical and thermal performance, structural integrity, manufacturability, and cost. Available details of the design, including materials, configuration, performance predictions, are presented.<<ETX>>

Prediction of burnout of a conduction-cooled BSCCO current lead

A one-dimensional heat conduction model is employed to predict burnout of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8/ current lead. The upper end of the lead is assumed to be at 77 K and the lower end is at 4 K. The results show that burnout always occurs at the warmer end of the lead. The lead reaches its burnout temperature in two distinct stages. Initially, the temperature rises slowly when part of the lead is in flux-flow state. As the local temperature reaches the critical temperature, it begins to increase sharply. Burnout time depends strongly on flux-flow resistivity.

Design and performance of low-thermal-resistance, high-electrical-isolation heat intercept connections

Electrical conductors often require the removal of heat produced by normal operation. The heat can be removed by mechanical connection of the conductor to a refrigeration source. Such connections require both effective heat removal (low thermal resistance) and effective electrical isolation (high electrical resistance and high dielectric strength). Fabrication of these connections should be straightforward, and performance must be reliable and independent of operating temperature. The connection method described here involves clamping (by thermal interference fit) an electrically insulating cylinder between an outer metallic ring and an inner metallic disc. Material candidates for insulating cylinders include composites, e.g. epoxy/fibreglass, and ceramics, e.g. alumina. Design factors, including geometry, materials and thermal contact resistance are discussed. The design, construction experience and performance measurements of a heat intercept connection in a high-temperature superconducting lead assembly is presented.

Engineering Design of A High-Temperature Superconductor Current Lead

As part of the U.S. Department of Energy’s Superconductivity Pilot Center Program, Argonne National Laboratory and Superconductivity, Inc., are developing high-temperature superconductor (HTS) current leads suitable for application to superconducting magnetic energy storage systems.

Characterization of high-current, high-temperature superconductor current lead elements

A conductor element consisting of laminated stack of high temperature superconductor (HTS) powder-in-tube (PIT) tapes is suitable for incorporation into current leads. The details of an application of such conductor elements to a current lead for a SMES system are presented. The fabrication of the laminated-conductor elements made with BSCCO 2223 PIT tapes is described. The critical current measurement method and results for two such conductor elements are presented. Performance was evaluated with variable temperatures and with variable applied fields.

Ultimate Strength, Low-Stress Creep Characteristics and Thermal Intercept Methods for an Epoxy-Fiberglass Tension Member Support

Superconducting magnet cryostats require low-heat-leak, structurally sound supports. A suitable geometry is that of a tension member support, which supports the cold mass of the magnet relative to the structure of the insulating vacuum vessel. This geometry permits configurations that can resist dynamic loading and can result in a support system whose preloading is independent of temperature.

An Epoxy Fiberglass Tension Member Support for Superconducting Magnets

As the state of the art of superconducting magnet system design advances, an accompanying challenge is the minimization of the heat leak to the magnet cold mass. Accordingly, a criterion to be applied is to achieve the condition where the heat transfer by the supports, thermal radiation, and penetrations produces only the amount of gas flow required to cool the magnet current leads. This paper describes one component of the solution to the problem, a low-heat-leak structural support system.

Performance evaluation of high-temperature superconducting current leads for electric utility SMES systems

As part of the U.S. Department of Energy`s Superconductivity Technology Program, Argonne National Laboratory and Babcock & Wilcox are developing high-temperature super-conductor (HTS) current leads for application to electric utility superconducting magnetic energy storage systems. A 16,000-A HTS lead has been designed and is being constructed. An evaluation program for component performance was conducted to confirm performance predictions and/or to qualify the design features for construction. Performance of the current lead assemblies will be evaluated in a test program that includes assembly procedures, tooling, and quality assurance; thermal and electrical performance; and flow and mechanical characteristics. Results of the evaluations to date are presented.

Thermal Resistance Across a Copper/Kapton/Copper Interface at Cryogenic Temperatures

The high-{Tc} superconductor current lead heat intercept connection, which is utilized as a thermal intercept to remove the Joule heat from the upper stage lead to a heat sink operating at 50--77 K, consists of a structure where a 152-{micro}m film is sandwiched between two concentric copper cylinders. The material chosen for the insulating film is Kapton MT, a composite film which has a relatively low thermal resistance, but yet a high voltage standoff capability. Here, the measured thermal conductance of a copper/Kapton MT/copper junction in a flat-plate geometry is compared to the results obtained from the actual heat intercept connection. Increasing the contact pressure reduces the thermal resistance to a minimum value determined by the film conduction resistance. A comparison between the resistance of the copper/Kapton MT/copper junction and a copper/G-10/copper junction demonstrates that the Kapton MT layer yields a lower thermal resistance while still providing adequate electrical isolation.