O. R. Christianson

Transient Electromechanical Modeling for Short Secondary Linear Induction Machines

Linear induction motors are under development for a variety of demanding applications including aircraft launchers and magnetically levitating trains. These applications require machines that can produce large forces, operate at high speeds, and can be controlled precisely to meet performance requirements. The design and implementation of these systems require fast and accurate techniques for performing system simulation and control system design. We present techniques for modeling and controlling linear induction machines based on a direct and quadrature (DQ) representation of the system dynamics. Simulation results using the DQ representation of the machine dynamics are presented and compared to test data from a Subscale Integration Test Bed developed for the U.S. Navys Electromagnetic Aircraft Launch System program.

Steady-state Hall losses in composite cryogenic conductors

Abstract Three distinct numerical methods are developed and evaluated for predicting the transverse Hall currents in long composite cryogenic conductors. These methods are applied to three different conductor geometries; a double-strip, a square-jacketed and a round-jacketed conductor. The double-strip geometry is used as a simple example to illustrate the Hall effect in composite conductors and to compare results from the three calculational methods. Earlier experimental results on the anomalous magnetoresistance of square-jacketed Al-Al alloy composite conductors are reanalysed using the present accurate numerical approaches. Improved agreement is obtained between experiment and theory compared with the earlier simplified models. Calculations and experimental data are shown for cases where the applied magnetic field is oriented at an angle with respect to the conductor. The calculated resistance variation with angle is shown to have the same form as the measured data. Good agreement is also obtained between the predictions of the closed-form analytical formulae of Kaneko and Yangai and the present finite element calculations for the Hall currents in Al-Cu round-jacketed composite conductors.

Conductor Selection for SMES Applications

The rationale for selection of a stabilized conductor for large scale superconducting magnetic energy storage applications (SMES) is discussed in this paper. Areas discussed are 1) stability, 2) AC losses, 3) manufacturability, 4) cooldown and warm-up, 5) protection, and 6) reliability for utility applications. It is concluded that a monolithic aluminum stabilized superconductor cooled in a bath of 1.8 K helium is the optimal choice.

Power loss in SSC dipole magnets during a current ramp

The instantaneous power and cyclic loss during current ramp of SSC dipole magnets are determined by a new procedure. The instantaneous power loss is calculated from the measured voltage times the current during a current ramp. An experimental procedure eliminates the inductive voltage component from the measured voltages by comparing voltages during a ramp up with voltages during a ramp down. Integral or cyclic power loss is found by integrating the instantaneous power loss over a cycle. A power loss due to decaying eddy currents is observed when the ramp stops and the magnet current is constant. Comparisons to integral or cyclic power loss without inductive voltage component compensation and theoretical calculations are made.

Design and Issues Associated with the HDM Electrical Insulation System

The Westinghouse Electric Corporation (WEC) is under contract to design and build the High Energy Booster dipole magnets (HDM’s) for the SSCL through low rate initial production (LRIP). The first phase of the HDM program is the fabrication and test of short 1.8 m HDM model magnets designed by the SSCL. This technology transfer phase is well underway with the delivery of the first WMSD built HDM model magnet, DSB701 to the SSCL and the completion of the test program conducted at the SSCL Superconducting Cable and Magnet Test Laboratory (SMCTL) in April of this year. This paper presents a summary of reverse engineering analyses of the HDM model magnet electrical insulation system performed by the WEC. The electrical stresses in the 2-D magnet cross section are estimated under rated voltage conditions for Hipot tests in air. A transient voltage analysis is presented for the ringer circuit Results of an analysis of quench voltage behavior as a function of protection circuit parameters is also presented. The lumped quench circuit model predicts the terminal and splice voltages, coil resistance, hot spot temperature, and MIITS. Deficiencies in the electrical insulation HDM model magnet design are addressed.

Thermal Analyses of the SMES ETM Power Bus Cryostat

In order to ensure reliable operation of the Superconducting Magnet Energy Storage Engineering Test Model (SMES-ETM), the conductor in the power bus must meet similar performance requirements as the entire coil during both steady state and transient operating modes. Lumped parameter thermal analyses are performed to evaluate steady state performance and assess risk involved with failure modes associated with the superconducting bus cryostat. Transient heat fluxes to the superfluid helium vessel are calculated for the loss of bus vacuum and the loss of nitrogen shroud cooling. The elapsed time to reach the critical heat flux in superfluid helium is calculated using the heat conductivity function for these cases. It is concluded that in the event of bus cooling failure, barring catastrophic loss of vacuum, the bus and cryostat can function for limited periods of time without interrupting ETM operations.

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.

He II Cooling System Performance in the Ebasco Proof of Principle Experiment during Lambda Transition, Warmup, and Quench

Temperature measurements in a 700 L bath of helium during cool down, the transition to He II, and operation in subcooled He II taken during the Ebasco SMES proof of principle experiment, POPE, are reported. Cooldown proceeds at a uniform rate throughout the bath, but the lambda transition appears to propagate from the heat exchanger to the current leads, which provide the largest heat load to the helium II region, over ten minutes. During warm-up and quench significant temperature stratification is observed with the bath consisting of boiling helium at the top and subcooled helium with decreasing temperature below. Both regions consist of a constant thickness while the helium level decreases as helium is vaporized at the top of the bath. The region of helium at the bottom of the dewar is at the lambda point, decreases in thickness with time, and exists for up to six hours after the He II heat exchanger is turned off. Calculations based on a model incorporating temperature dependent density and thermal conductivity of helium matches the measurements. This behavior is also observed during quench at an accelerated time scale.

He II refridgeration system performance in the SMES proof of principle experiment

Abstract The system performance of the He II refridgeration system used in the Ebasco team SMES proof of principle experiment is described. The system ultimately achieved a temperature of 1.85 K at a heat load of 37 W, and ran for 30 h without any problem. System elements requiring special attention, including the heat exchanger design, thermal penetrations, pumping, and plumbing, are discussed. Operating characteristics involving cooldown, lambda transition, and thermal perturbations are described.

Design and Projected Performance of the Westinghouse µSMES Unit

The Westinghouse design of a 5 MJ, 2 MW, 2 second discharge µSMES unit is described in this report. The magnet consists of concentric, potted coil modules, each with a support structure designed to limit eddy currents. It operates in a bath of liquid helium. The individual modules are wound with a superconducting Rutherford cable which operates at 1500 amperes in a peak field of 3.5 T. The coil modules are layer wound and potted with the support structure. The magnet is designed so that it will not quench during discharge and the subsequent charge. This performance is calculated by determining the losses due to hysteresis and eddy currents and the resulting temperature rise. The magnet current is compared to the temperature and field dependent critical current to determine that the superconductor has adequate stability margin to prevent a quench. Losses are reduced by using a Rutherford cable and by controlling the interstrand resistance. When fully charged, adequate margin ensures superconducting operation of the magnet where the conductor margin is found by comparing the operating point to the critical surface. The quench current and field are determined from the intersection of the magnet load line and the superconductor critical surface. Magnetic field calculations are performed with the finite element code MAFCO, and the superconductor critical surface is defined by an empirical relationship. Although no quenches are expected during normal operation, a quench detection circuit and protection resistor are provided so that the temperature rise, estimated from the MIITS generated at a selected discharge voltage, is small ensuring no magnet damage. Joint design, operation, and margin are also described in this paper.