C. M. Rey

Status of Conductor Qualification for the ITER Central Solenoid

The ITER central solenoid (CS) must be capable of driving inductively 30 000 15 MA plasma pulses with a burn duration of 400 s. This implies that during the lifetime of the machine, the CS, comprised of six independently powered coil modules, will have to sustain severe and repeated electromagnetic cycles to high current and field conditions. The design of the CS calls for the use of cable-in-conduit conductors made up of and pure copper strands, assembled in a five-stage, rope-type cable around a central cooling spiral that is inserted into a circle-in-square jacket made up of a special grade of high manganese stainless steel. Since cable-in-conduit conductors are known to exhibit electromagnetic cycling degradation, prior to the launch of production, the conductor design and potential suppliers must be qualified through the successful testing of full-size conductor samples. These tests are carried out at the SULTAN test facility. In this paper, we report the results of the on-going CS conductor performance qualification and we present the options under consideration for the different modules constituting the CS coil.

Electrical AC Loss Measurements on a 2G YBCO Coil

Oak Ridge National Laboratory (ORNL) is collaborating with Waukesha Electric Systems (WES) to continue development of HTS power transformers. Second-generation (2G) YBCO coated conductors will be required for an economically-competitive design. In order to adequately size the refrigeration system for these transformers, the ac loss of these HTS coils must be characterized. Electrical ac loss measurements were conducted on a prototype high voltage (HV) coil with co-wound stainless steel at 60 Hz in a liquid nitrogen bath using a lock-in amplifier technique. The prototype HV coil consisted of 26 continuous (without splice) single pancake coils concentrically centered on a stainless steel former. For ac loss measurement purposes, voltage tap pairs were soldered across each set of two single pancake coils so that a total of 13 separate voltage measurements could be made across the entire length of the coil. AC loss measurements were taken as a function of ac excitation current. Results show that the loss is primarily concentrated at the ends of the coil where the operating fraction of critical current is the highest and show a distinct difference in current scaling of the losses between low current and high current regimes.

Testing of an HTS Power Cable Made From YBCO Tapes

Oak Ridge National Laboratory (ORNL) has designed, built, and tested a 1.25-m-long, prototype high temperature superconducting (HTS) power cable made from second-generation YBa2Cu3Ox (YBCO)-coated conductor tapes. Electrical tests of this cable were performed in liquid nitrogen at 77 K. DC testing of the HTS cable included determination of the V-I curve with a critical current of about 2100 A, which was consistent with the critical currents of the two layers of 4.4-mm wide YBCO tapes. AC testing of the cable was conducted at currents up to about 1500 Arms. The ac losses were determined electrically by use of a Rogowski coil with a lock-in amplifier. Over-current testing was conducted at peak current values up to 4.9 kA for pulse lengths of 0.3-0.5 s. Test results are compared to earlier data from a 1.25-m-long power cable made from 1-cm-wide YBCO tapes and also comparable BSCCO cables. This commercial-grade HTS cable demonstrated the feasibility of second-generation YBCO tapes in an ac cable application.

Addressing the Technical Challenges for the Construction of the ITER Central Solenoid

The Central Solenoid (CS) of the ITER Magnet system is split into six independently powered coils enclosed inside an external structure which provides vertical precompression thus preventing separation of the coils and acting as a support to net resulting loads. The analyses include an assessment of the mechanical behavior of the different components of the CS, under the normal and fault conditions, aiming at demonstrating the ability of the CS to achieve 30 000 cycles of plasma operation at nominal current (15 MA). A comprehensive material testing program is developed for the conductor jacket, the impregnated glass-epoxy insulation and the structure. The paper describes the architecture of the analysis and qualification programs and provides an overview of the results obtained so far.

TEST RESULTS FOR A 25 METER PROTOTYPE FAULT CURRENT LIMITING HTS CABLE FOR PROJECT HYDRA

The Oak Ridge National Laboratory (ORNL) has tested a 25‐m long prototype High Temperature Superconducting (HTS) cable with inherent Fault‐Current Limiting (FCL) capability at its HTS cable test facility. The HTS‐FCL cable and terminations were designed and fabricated by Ultera, which is a joint venture between Southwire and nkt cables. System integration and HTS wire were provided by American Superconductor Corporation who was the overall team leader of the project. The ultimate goal of the 25‐m HTS‐FCL cable test program was to verify the design and ensure the operational integrity for the eventual installation of a ∼200‐m fully functional HTS‐FCL cable in the Consolidated Edison electric grid located in downtown New York City. The 25‐m HTS‐FCL cable consisted of a three‐phase (3‐Φ) HTS Triax™ design with a cold dielectric between the phases. The HTS‐FCL cable had an operational voltage of 13.8 kV phase‐to‐phase (7967 V phase‐to‐ground) and an operating current of 4000 Arms per phase, which is the highe...

Testing of a Liquid Nitrogen Cooled 5‐meter, 3000 A Tri‐Axial High Temperature Superconducting Cable System

The tri‐axial HTS cable design uses three concentric superconducting layers for the phase conductors separated by a cold dielectric material. It offers an efficient HTS cable configuration by reducing the amount of superconductor needed, and placing all three phases in a single cryostat. Ultera and ORNL tested a 5‐meter long tri‐axial HTS cable and terminations designed to operate at 3 kA ac and 13.2 kV. Test results, including the thermal loads on the system, will be reported. An existing liquid nitrogen skid that circulates subcooled liquid nitrogen through the cable was initially designed for the heat loads on single phase cables at lower current ratings. The refrigeration needed for the 3 kA tri‐axial cable configuration made it necessary to upgrade the nitrogen system to increase the cooling capacity. A description of the upgrades and performance of the system is provided.

Testing of 3-Meter Prototype Fault Current Limiting Cables

Two 3-m long, single-phase cables have been fabricated by Ultera from second generation (2G) superconductor wire supplied by American Superconductor. The first cable was made with two layers of 2G tape conductor and had a critical current of 5,750 A while the second cable had four layers and a critical current of 8,500 A. AC loss was measured for both cables at ac currents of up to 4 kArms. Ultera performed initial fault current studies of both cables in Denmark with limited currents in the range from 9.1 to 44 kA. Results from these tests will provide a basis for a 25-m long, three-phase, prototype cable to be tested at ORNL early next year and a 300-m long, fault current limiting, superconducting cable to be installed in a Consolidated Edison substation in New York City.

Quench in High-Temperature Superconducting Motor Field Coils: Experimental Results at 30 K

The results of quench tests on high-temperature superconducting (HTS) motor coils conduction-cooled to 30 K are presented. In previous tests, the same coils were cooled by direct immersion in liquid nitrogen. In spite of both a significantly lower temperature and a different cooling mechanism, the 30 K tests confirm the previous results which showed that the quench process is characterized by a current level, referred to as the quench current, above which the cooling system cannot maintain the winding temperature. Currents in excess of this value will produce an unstable growth in winding temperature in a process commonly referred to as a coil quench.

Current-Voltage Measurements in a 2G YBCO Coil

The Oak Ridge National Laboratory in collaboration with American Superconductor Corporation and Cryomagnetics Inc. has designed, fabricated, and tested an HTS coil wound with second-generation (2G) YBCO coated conductor tape. The purpose of the HTS coil project was to study the quench characteristics in 2G YBCO coils at 77 K and lower temperatures (~30-45 K). These quench characteristics were investigated in both a pool boiling LN2 environment and in a conduction cooled configuration at ~30 K and 45 K. Transport critical current (Ic) measurements taken on the very first thermal cycle of the YBCO coil in pool boiling LN2 showed an Ic~31 A corresponding to a central magnetic field of 0.32 T. The measured Ic value was consistent with the calculated value using the calculated maximum perpendicular B-field component and the measured short sample Ic at 77 K. Subsequent Ic measurements taken in the conduction cooling configuration at 34 K and 45 K, showed a steady-state Ic~45-49 A and 38-44 A, respectively. These Ic values were significantly lower than the calculated value assuming a literature derived temperature dependent Ic of the 2G YBCO tape. A steady degradation was observed in the Ic of the coil with each successive thermal cycle. In addition, the coil was also pulse tested up to 1-T in non-steady state transient conditions and for ramp rates varying between 0.01 and 5 A/s. The issues and limitations encountered during testing of this new type of 2G coil are briefly discussed.

Conceptual design of a novel industrial-scale HTS reciprocating high gradient magnetic separator

Reciprocating magnetic separators are used in the purification of kaolin clay and titanium dioxide. Design parameters and fabrication details are reported for the high temperature superconducting (HTS) coil. The HTS coil is 0.7 m in length and has a 0.5 m inner diameter. The central operating magnetic field is a nominal 3.0 T with a design operating current of 100 A. In terms of combined size and magnetic field strength, this is one of the largest HTS magnets ever fabricated, possessing a stored energy > 0.400 MJ. The HTS magnet is conduction cooled via single-stage G-M cryocoolers with a nominal operating temperature of 30 K. The HTS conductor uses a stainless steel reinforced Bi-2223 material. Salient features and results of the electromagnetic and thermal analyses are discussed.