Yunfei Qiao

High Performance 2G Wires: From R&D to Pilot-Scale Manufacturing

Tremendous progress has been accomplished in 2008 in key metrics of YBa2Cu3Ox (YBCO) second-generation (2G) HTS wires at SuperPower. Using improved precursor chemistry in our metal organic chemical vapor deposition (MOCVD) process, critical currents (Ic) as high as 813 A/cm were reached over meter-long lengths, representing the highest reported Ic in meter long 2G HTS. By use of Zr doping of (Gd,Y)Ba2Cu3Ox, strong enhancements were achieved in in-field performance over a wide angular range. A Ic of 229 A/cm was achieved at 77 K and 1 T perpendicular to the wire which is about a factor of 2.5 times better than that of standard MOCVD-derived films. At 65 K and 3 T, a Ic of 340 A/cm was demonstrated perpendicular to the wire. Kilometer lengths of 2G HTS have been demonstrated for the first time. Over 35 tapes 1,000 to 1,500 m in length with a complete 5-layer buffer stack have been routinely produced in our pilot-scale manufacturing facilities. An excellent in-plane texture of 6 to 7 degrees with a uniformity of about 2% was reproducibly achieved in the kilometer-long fully-buffered tapes. Using these high-quality buffers, the longest 2G wire length to date of 1,311 m was produced with a minimum Ic of 153 A/cm corresponding to a Ic times length value of 200,580 m. Also, an 1,030 m long complete 2G HTS wire has been demonstrated with a minimum Ic of 227 A/cm corresponding to a record Ic times length value of 233,810 A-m. Further, a 630 m long segment of the wire sustained a minimum Ic of 302 A/cm, the longest 2G wire reported to date with a Ic over 300 A/cm. Also, a Ic of 337 A/cm was achieved over a 540 m long segment. All these values represent a 2 to 3 fold improvement in length and Ic of 2G wires compared to our achievements in 2007. In 2008, a 30 m long 2G cable made with nearly 10,000 m of 2G wire previously delivered by SuperPower was successfully installed and energized in the grid of National Grid in downtown Albany, marking the worlds first of 2G HTS device in the power grid.

Recent Progress in Second-Generation HTS Conductor Scale-Up at SuperPower

YBa2Cu3Ox (YBCO) second-generation (2G) HTS conductors have been produced in lengths over 300 m in pilot scale facilities established at SuperPower. High throughput pilot-scale manufacturing has been demonstrated with tape speeds at or above 30 m/h of 12 mm wide tape (corresponding to 90 m/h of 4 mm wide conductor) in all steps. A 322 m long conductor with a minimum critical current value of 219 A/cm has been produced, which corresponds to a critical current x length value of 70,520 A-m. A 270 m long, 4 mm wide conductor with an end-to-end critical value of 100 A has also been demonstrated. In a campaign to manufacture 2G conductor for the Albany cable project, SuperPower has produced 12,470 m of conductor that meets or exceeds the specification for piece length (42.4 m) and critical current (100 A/cm). In fact, more than 55% of the conductor produced is at least 100 m in piece length and more than 27% greater than 200 m in piece length. In addition to scaling up 2G conductors to high-throughput pilot-scale manufacturing, we have demonstrated high critical currents in short samples produced by Metal Organic Chemical Vapor Deposition (MOCVD). Critical current values of 557 A/cm have been achieved in 2.1 micrometer thick films in 12 mm wide, 10 cm long tapes. These samples exhibit a critical current value of 116 A/cm at 1 T and 76 K, in the orientation of field parallel to the c-axis. We have also constructed a 4-pancake coil that generated a magnetic field of 1.1 T at 77 K and 2.4 T at 64 K. A Fault Current Limiter (FCL) assembly has been successfully constructed and tested at high power levels. A prospective current of 90 kA was successfully limited to 32 kA within 1 ms without any HTS element failure.

High Throughput Processing of Long-Length IBAD MgO and Epi-Buffer Templates at SuperPower

SuperPower has successfully transferred from low throughput IBAD (Ion beam assisted deposition) YSZ technology to high throughput IBAD MgO technology. Pilot-scale IBAD system and pilot-scale epi-buffer deposition system, each with capabilities of producing single-piece lengths over 1000 m have been established. Helix tape handling approach instead of wide tape approach is chosen due to its immense advantages over wide tape approach. High-performance IBAD MgO buffer stack and their processes have been developed together with high throughput where each layer in the buffer stack is processed at 40 m/h tape speed or higher during our Phase I scale up. Both pilot systems are in routine production mode since March 2006. More than 14 km IBAD MgO buffer tapes of 12 mm width were produced for Albany cable project. 700-800 m IBAD MgO tape per run is routinely produced in pilot IBAD system with single piece tape length ~570 m. 400-550 m epi-buffer tape per run is routinely produced in pilot buffer system. High throughput IBAD MgO buffer gives better texture of YBa2Cu3O7 (YBCO) film compared with IBAD YSZ, and superior superconducting properties. A high critical current of 557 A/cm in short tapes and a world record critical current times length value of > 70, 000 A - m were obtained with the high throughput IBAD MgO buffers.

Second-Generation HTS Conductor Design and Engineering for Electrical Power Applications

Besides critical current and conductor length, thermal stability, mechanical properties and ac loss characteristics of second-generation (2G) HTS wire are very important performance parameters to electric power device applications. Each application sets specific technical requirements on conductors. The properties of the practical 2G HTS wire manufactured at SuperPower, Inc. have enabled satisfactory performance in a number of demonstration devices including cable, high-field magnetic coil and fault current limiter. Yet, effort is being made to develop new conductor structures and configurations toward further enhanced performance in order to extend the potential of 2G HTS wire over a wider application range. This paper describes a variety of newly developed configurations: striation, narrow width, low-resistance joints and high quality insulation. The performance of wire with new configurations will promote the wide use of 2G HTS wire.

Scale Up of Coated Conductor Substrate Process by Reel-to-Reel Planarization of Amorphous Oxide Layers

Substrate surface smoothness comparable to electropolished substrate has been demonstrated by planarization of multilayers of amorphous oxide films on as received flexible metal tapes. An in-plane texture of 6.4 degrees was achieved on short samples after the final buffer process. A critical current density (Jc) over 3 MA/cm2 has been achieved on short samples. The planarization process has been scaled up from a few meters previously done by loop coating to be capable of producing 100 meters. 20 m of planarized substrate were processed with standard buffer deposition process and metal organic chemical vapor deposition (MOCVD) manufacturing run. An average in-plane texture of eight to nine degrees was obtained on the entire 20 m piece after the final buffer LMO process. A uniform critical current (Ic) of 160 A was achieved on 15 m. The planarization process has the potential to lead to a reduction in buffer layers and alleviate the burden of hazardous waste generated from the electropolishing process. It is capable of planarization of any substrate alloy, while electropolishing is limited to only a few alloys.

RECENT PROGRESS IN SECOND-GENERATION HTS WIRE TECHNOLOGY AT SUPERPOWER

We report recent progress in 2G-HTS wire technology at Superpower Inc. The throughputs of 4mm-wide tape have reached 750m/h for sputtering Al O 3 +Y 2 O 3 base layer, 360m/h for IBAD MgO template, 345m/h for sputtering Homo-epi MgO+LMO buffer, 180m/h for MOCVD REBCO. Critical current (Ic) of 813A/cm-width at 77K and self-field has been achieved on 1 meter length of 12mm-wide tape in which the thickness of GdYBCO film is 3.3 microns. Ic in a magnetic field has been significantly improved through composition modification, doping and MOCVD condition optimization. Ic of 185.6A/cm-width at 77K and 1Tesla has been obtained. For Ic on long lengths, 314A/cm-width on 202m, 221A/cm-width on 610m and 170A/cm-width on 935m have been achieved. A coil of 19.1mm diameter we made with our 2G wires generated 26.8T magnetic field in the magnet. A 30m-long cable made with nearly 10,000 meters of Superpower 2G wires showed excellent overall performance and has been installed and energized in the power grid.

Second-generation HTS wire manufacturing and technology advancement at superpower

REBa2Cu3O7−δ (REBCO) coated conductor, namely second generation high-temperature (2G HTS) wire, holds enormous promise for many real world applications such as electrical power transmission cables, superconducting magnets, energy storage, fault current limiters, motors, generators and medical devices. SuperPower is developing and manufacturing high-performance 2G HTS wire based on two high-throughput processes: IBAD-MgO for texture buffer and MOCVD for the HTS layer. Tremendous progress has been made in 2G HTS wire technology development and manufacturing in the past few years. In this paper, we report our overall achievements in kilometer long wire fabrication reaching a minimum Ic of 282 A/cm-w over 1,065 m, practical conductor development for ac application and recent achievement in high-field coils and quench detection technique.