TECHNOLOGY AREA(S): Battlespace, Electronics, Sensors

ACQUISITION PROGRAM: PMS406, Unmanned Maritime Systems Program Office

OBJECTIVE: Develop and demonstrate an innovative method to detect, prevent, and protect high-inductance, High Temperature Superconducting (HTS) coils from damage that would normally occur in a quench event.

DESCRIPTION: The Navy has been developing high-temperature superconducting (HTS) systems, such as large-scale motors or large-scale magnets, over the past few decades using HTS coils. Superconducting magnets utilizing alternating current (AC) modulation do not have any quench detection capabilities, putting the system at risk for damage due to uncertain superconducting-state health.

HTS wire has the ability to pass large electrical currents with essentially no voltage drop due to its zero resistance when below the transition temperature. Therefore, there is tremendous advantage to use HTS technology in applications generating large magnetic fields such as, high-field magnets, motors, generators, and superconducting magnetic energy storage (SMES) systems. However, when high-temperature superconductors are used in these aforementioned applications, there is significant operational risk to an HTS coil in the event of a quench. For superconducting power cables, a quench event is not as critical as that of a magnet-based system which inherently stores large amount of inductive energy. In the field of HTS technology, a �quench� is when an HTS conductor transitions from its superconducting state to its normal-conducting resistive state. Typically, the transition initiates in a local region referred to as �normal zones�. Depending on the design of an HTS magnet, individual coils may be replaced, or repaired; however, this is very costly, and time consuming, and does not guarantee that the HTS magnet will be operational upon completion of an attempted repair. Methods to detect the onset of a quench, prevent a quench from occurring, and/or protect the HTS coil from damage must be employed to safeguard HTS coils.

High-field HTS magnets have large electrical inductances that store mega-joules of energy. When a quench occurs, this energy converts to heat in the normal zone of the conductor and has the potential to cause a burnout in the HTS coil. The current method of quench monitoring and protection system technology measures the voltage drop across the HTS coils. When the voltage exceeds a set threshold, the energy in the coils is �dumped� to a resistive load to protect the coil from quenching. The limitation with this type of system is a delay between 500ms to 1000ms to detect the onset of quench, and rate of energy extraction to protect the coils. Furthermore, since voltage measurements are typically taken over long conductor lengths, indicators of a localized quench may be masked causing a delayed response. In addition, when an HTS magnet is used as an AC magnetic source or as a pulsed current source, the differential voltage across a coil could reach kilovolt levels that are difficult for simple quench detection data acquisition hardware to manage.

The proposed solution technology is expected to be applicable to superconducting magnet payloads, HTS motor and generator field and stator coils, and pulsed current SMES systems subject to alternating currents. The quench monitoring and control system must provide adequate quench detection, prevention, and protection to both direct current (DC) and AC HTS coils. The system must also provide a safe shutdown sequence in the event a quench occurs. The solution must have the ability to be integrated with HTS coils and their sub-systems, operate with HTS magnet controls, and be fully operational in a naval environment.

Since initial target application is for integration into an HTS system as a payload on an Unmanned Surface Vehicle (USV), compact and lightweight solutions (i.e., standard 19� rack mount, on the order of 50-70lbs) are favorable. The quench monitoring and control system should be able to detect a quench within 80ms. It should be able to operate in magnetic applications with voltages ranging from 0V to �12kV and AC frequencies ranging up to 60Hz. Any hardware or sensors mounted to the HTS coils should be able to operate at magnetic fields up to 5T, and any hardware or data acquisition systems should be shielded from magnetic fields up to 1T. The proposed solution should be effective with coils wound from tens of meters to tens of kilometers of wire or more. In addition, any proposed hardware or sensor solutions mounted to the HTS coils should be able to operate in temperatures from 20K to 100K (-253�C to -173�C), and must be able to be integrated into a cryogenic cryostat containing the magnet coil. Any auxiliary hardware or data acquisition systems external to the cryostat must operate in atmospheric air temperatures from -20�C to 46�C, cooling water from 4�C to 40�C, humidity levels from 0% to 100%, and salt fog conditions as listed in MIL-STD-810G (Section 509.5) [Ref 4]. Finally, all proposed solutions must be capable of withstanding military shock specifications as listed in MIL-S-901D Grade A [Ref 5] and military vibration standards listed in MIL-STD-167-1A [Ref 6].

PHASE I: Define and develop a quench detection, prevention, and protection concept that meets the objectives stated in the Description. Demonstrate the feasibility of the proposed concept through modeling and analysis. Quantify the clear benefits in terms of speed to detect, prevent, and protect an HTS coil as compared to existing voltage measurement solutions [Ref 2]. Develop size and weight objectives of proposed concepts including sensors and control electronics. Develop a Phase II plan. The Phase I Option, if exercised, will include the initial layout and capabilities description to build the prototype in Phase II.

PHASE II: Develop and fabricate a prototype for demonstration and characterization of key parameters of the quench control system as described in the Description. Conduct a prototype demonstration capable of full-scale operation according to the design. Complete relevant testing to prove the full-scale metrics. Based on lessons learned through the prototype demonstration, develop a substantially complete design of a quench control system to allow for Navy integration. Ensure that this design includes all ancillary equipment required to operate components such as the quench control system, integration hardware, and control software when applicable to the proposed concept.

PHASE III DUAL USE APPLICATIONS: Support the Navy in transitioning the technology for Navy use. Although a fully operational quench control system is initially targeted for use in an HTS system as a payload aboard a USV, the quench control system should have the ability to transition to any naval acquisition program utilizing HTS coils as either a major system or as a sub-system to a larger program.

The desired quench control system has applications in commercial large-bore superconducting magnets used in the medical field, large-particle accelerators, and superconducting motor applications. A simpler design of the quench control system could also be applied to superconducting power distribution, superconducting electric grids and alternative energy technologies using superconducting systems.

REFERENCES:

1. Scurti, F., Ishmael, S., Flanagan, G., and Schwartz, J. �Quench Detection for High Temperature Superconductor Magnets: a Novel Technique Based on Rayleigh-backscattering Interrogated Optical Fibers.� Superconductor Science and Technology, Volume 29, Number 3, March 2016. http://iopscience.iop.org/article/10.1088/0953-2048/29/3/03LT01

2. Marchevsky, M. �Protection of Superconducting Magnet Circuits.� U.S. Particle Accelerator School (USPAS) Course Material, UC Davis, January 2017. http://uspas.fnal.gov/materials/17UCDavis/MachineProtection/uspas_mm.pdf

3. Wakuda, T., Ichiki, Y., and Park, M. �A Novel Quench Protection Technique for HTS Coils.� IEEE Transactions on Applied Superconductivity, Volume 22, Issue 3, June 2012. http://ieeexplore.ieee.org/document/6111204/

4. MIL-STD-810G (sect 509.5), Department of Defense Test Method Standard: Environmental Engineering Considerations and Laboratory Tests. http://everyspec.com/MIL-STD/MIL-STD-0800-0899/MIL-STD-810G_12306/

5. MIL-S-901D Grade A, Military Specifications: Shock Tests H.I. (High-Impact) Shipboard Machinery Equipment, and Systems, Requirements for. http://everyspec.com/MIL-SPECS/MIL-SPECS-MIL-S/MIL-S-901D_14581/

6. MIL-STD-167-1A, Department of Defense Test Method Standard: Mechanical Vibrations of Shipboard Equipment. http://everyspec.com/MIL-STD/MIL-STD-0100-0299/MIL-STD-167-1A_22418/

KEYWORDS: High Temperature Superconductor; High-field Magnets; SMES; Quench Detection; Quench Prevention; Quench Protection; Superconducting Magnetic Energy Storage