Donald T. Hackworth

Structural considerations and analysis results for a large superconducting magnetic energy storage device

A description of the conceptual design for the magnet structure of a large superconducting magnetic energy storage (SMES) device is presented. This work is part of a program to select the best design for a 21-MWh unit. The coil structure is a four-layer solenoid design with a mean radius of 219 ft and carries a current of 50000 A. The structure design selected and the tradeoffs among different geometries are described. The results of a parametric finite-element and closed-form stress analysis are given in order to compare different rippled coil geometries in terms of structure stresses and cyclic conductor strain. The effects of ripple radius and strut spacing are given for the cooldown, normal operation, and quench conditions.

Design and construction of the 4 Tesla background coil for the navy SMES cable test apparatus

The design and construction of a background coil being built by Westinghouse STC for the Navy SMES cable test apparatus are presented. One objective of the Navy SMES development program is to develop and test improved superconductors for SMES use. The background coil generates a 4 Tesla field on a 1.85 meter diameter SMES conductor sample. The coil stores 49.4 MJ, and has an inner diameter of 2.13 meters. The background coil and SMES conductor sample are housed in separate, concentric cryostats so that the SMES conductor samples can be changed without warming the background coil. The background coil is a pancake style winding, utilizing a Rutherford cable conductor cowound with a stainless steel strap and mylar insulation.

Designs of pulsed power cryogenic transformers

The design of three pulsed-power cryogenic transformers for the Los Alamos National Laboratory is summarized. The design uses two-layer air core, solenoid-type pulse transformers. Cooling will be accomplished through pool boiling in a liquid-nitrogen bath, with heat-transfer surfaces sized to accommodate the required repetition rate. These transformers are configured to transfer their stored energy sequentially to an electro-magnetic launcher and form a three-stage power supply. The pulse transformers will act as two-winding energy-storage solenoids which provide a high current and energy pulse compression by transforming a 50-kA power supply into a megamp-level power supply more appropriate for the electromagnetic launcher duty. This system differs from traditional transformer applications in that significant current levels do not exist simultaneously in the two windings of the pulse transformer. >

Advantages of the distributed structure concept of the Westinghouse LCP coil design-II

The forced flow Nb 3 Sn magnet concept developed by Westinghouse in cooperation with the Oak Ridge National Laboratory offers the fusion program the option of a reactor size superconducting toroidal field coil which has the capability of achieving peak fields of 12 tesla. The Westinghouse LCP coil concept offers a number of advantages besides high field capability. The coil is fabricated by winding stainless-steel-jacketed conductors into machined slots in the structural plates. This configuration provides positive conductor support and prevents accumulation of magnetic loading on individual conductors. Another advantage of this concept is the distribution of the conductors which results in more uniform current density in the overall coil cross-section. This distributed winding approach also provides higher fields on the plasma axis for given peak fields on the conductor. The distributed structure uniformly distributes eddy current losses and has lower losses than lumped structure concepts when subjected to the pulsed poloidal fields. The higher current densities possible, due to more efficient utilization of space coupled with the use of materials with good radiation properties (materials used for the Westinghouse LCP coil), allows for reduction in reactor size, which can be a substantial cost advantage. The modular concept of the Westinghouse coil allows for parallel manufacturing operations. The maintainability and repairability aspects of the coil are also discussed.

Design of a 400-kJ Pulsed Energy Storage Coil

The design of the conductor for the 400-kJ, 25-kA pulsed energy storage coil [1], being built by Westinghouse for the Los Alamos Scientific Laboratory, differs significantly from the conductor fabricated previously for a 300-kJ coil [2] because of the low-loss requirements and fast pulse rate. As a consequence of the short discharge interval and low-loss requirements, the conductor in this application has a low copper-to-superconductor ratio.

Winding of the Navy SMES background coil

The Navy SMES background coil was made by stacking 18 double pancakes and connecting them in series to form a superconducting magnet capable of storing 48 MJ of energy. Each double pancake was wound starting in the middle of the conductor and winding outward for each layer. Insulators were placed between each pancake layer which were also used for lifting support. Instruments for the coil protection system control and magnetic field monitoring were attached after final assembly.

High voltage breakdown measurements of a large area SMES-ETM mockup in gaseous helium and air

Breakdown voltage measurements of a SMES-ETM (superconducting magnet energy storage-engineering test model) mockup are presented for gaseous helium and air at room temperature. The mockup dimensions are 1.35 m long by 0.15 m high. Four critical configurations are simulated (layer-to-layer, dewar-to-layer, coil-to-dewar and turn-to-turn) under four pressure conditions (0.25, 0.5, 0.75 and 1.0 atmospheres). The experimental results for the first three configurations are in rough accord with published data of breakdown voltages in air and helium (Paschen curve). The thin G-10 insulation layer of the fourth configuration provides an excellent insulation capability. Experimental breakdown voltages are compared to worst-case design specifications at one atmosphere. All worst-case safety factors exceed 10. The results indicate that design voltage specifications are adequate for operation in a worst-case quench scenario at one atmosphere helium.<<ETX>>

DESIGN AND ANALYSIS OF SMES-ETM ELECTRICAL INSULATION

The mechanical design and the electrical field analysis of the Ebasco/Westinghouse SMES-ETM coil electrical insulation system are presented. The electrical insulation design of the coil includes the turn to turn, layer to layer, and between the coil to the wall of the liquid helium vessel of the cryostat. A finite element analysis code (WEMAP) was used to obtain detailed electrical field plots of the high electrically stressed regions of the coil. These analytical results were used in conjunction with the experimental data of dielectric breakdown, available in the literature or obtained by in-house testing, to determine the optimum configuration and materials of the insulation spacers. An adequate design safety factor between the insulation capability and the maximum operating electrical stress was adopted to ensure the design integrity under all operating conditions and to allow for the uncertainties of the experimental dielectric breakdown data.

Pulsed HTS Coil Performance

HTS coils designed to carry pulsed currents have been built and tested demonstrating fast charge and discharge times on the order of a second. Gaseous Helium from 40 to 80 K is used as a coolant. Losses due to ac, hysteresis, and transport currents associated with current entry into and exiting from HTS are small and do not produce thermal transients that induce current sharing or normal transitions for reasonable margins and operating temperatures. Short lengths of HTS and small coils show current sharing before normal transitions, whereas current sharing voltages are not identified in large coils since current sharing voltages are small compared to inductive and resistive voltages. Pulse shape, duration, and frequency are varied with no degradation in performance.

Design of a Monolithic 15 kA Superconductor for SMES

The configuration and projected performance of a 15 kA monolithic superconductor designed for 0.36 to 72 GJ (0.1 to 20 MW-hr) SMES use for the Naval Surface Warfare Center is described. The conductor operates at 4.2 K and 1 atmosphere in a peak magnetic field of 5 T at 70% along the load line, which corresponds to a temperature margin of 1.7 K. The conductor consists of a Nb-Ti copper composite Rutherford cable soldered into a high purity aluminum stabilizer that has a nominal RRR of 1500. The conductor is cryogenically stable at the operating point. Pulsed devices and energy storage systems using superconductors require conductors with low AC losses. Internal eddy current barriers limit AC losses during a discharge. Extrapolation of the conductor configuration to further reduce AC losses is considered. A possible test configuration for the conductor is described as it is related to design specifications.