August 02, 2015

Magnesium diboride superconductors can lower the cost of wind turbine generator coils by over fifteen times

In January 2001, it was announced that MgB2 (magnesium diboride), a compound that was well known to chemists, was superconducting up to 39 Kelvin. Building on this discovery, Hyper Tech was formed in 2001 to use the compound to create a high-performing, low cost superconducting wire. Hyper Tech developed and patented a continuous tube forming and filling (CTFF) process for the manufacturing of a powder metallurgy-based MgB2 superconductor wire.

Hyper Tech is the world leader in manufacturing and R and D of magnesium diboride and niobium tin superconducting wire and integrated products. Hyper Tech’s innovative, patented wire drawing process enabled the company to be the first to manufacture viable long-length MgB2 wire. Hyper Tech has consistently integrated this technology into transforming products benefiting from superconducting materials. Superconductors carry high current with near zero ohmic loss. In coil form, such as in an electromagnet, a charged and closed loop can carry current, and hence magnetic field, for long periods of time (of the order of months to years depending on the detail design). This makes a superconductor ideal for high field magnets. It is commonly used in MRI and nuclear magnetic resonance (NMR) systems throughout the world. Hyper Tech is well equipped to produce two wire formed superconductors: MgB2 and Nb3Sn.

Hyper Tech's 41,000-square-foot facility contains the equipment necessary to manufacture MgB2 superconducting wire of varying diameters and lengths. A team of engineers, scientists and technicians has been assembled to develop and produce the superconducting wires and related products including superconducting coils for various applications. Hyper Tech is marketing MgB2 superconductor wires for MRI applications and has cooperative relationships with several companies to apply MgB2 superconductor wire to MRI devices. This commercial market has allowed Hyper Tech to lower the wire production cost to be economical for power systems applications as well (e.g., FCLs and wind turbines).

A solenoid coil fabricated in 2012 was wound with 590 meters of MgB2 multifilamentary wire. This coil achieved a peak bore field of 4.6 Tesla at 4 Kelvin and 2.2 Tesla at 20 Kelvin.

The advantage of MgB2 magnets when compared with permanent magnets is the possibility of achieving magnetic field strengths of considerably more than 0.4 Tesla (to 1.5-2.0 Tesla) with a lower initial capital equipment cost and lower life-cycle cost. Also, higher field strengths and larger zones of homogeneous magnetic field can be achieved with MgB2 superconductor than with permanent magnets. Compared with superconductors that operate at lower temperatures, such as NbTi and Nb3Sn, the life-cycle costs of MgB2 coils are lower because of their higher operating temperature and lower associated refrigeration costs during operation. In the on-going effort to eliminate liquid cryogen from equipment, the temperature tolerance of MgB2 better suits it for dry operation using only a cryocooler and conduction cooling.MgB2 conductors have many distinct advantages when compared with high temperature ceramic conductors. Since the wire can be configured in either round or rectangular cross sections, MgB2 adds flexibility in coil design and fabrication. MgB2 is lighter weight and can be produced at a lower cost than the high temperature ceramic BSCCO or YBCO-coated superconducting tape conductors when operated in the 20 Kelvin range. MgB2 wire is versatile in that it can be sized (e.g., to custom amperage and engineering current density) for targeted coil dimensions and performance. MgB2 wire behaves more like a metal superconductor with regard to persistent current type coils unlike high temperature superconducting tapes.

Up to 200 kilometers of coil is needed to generate electricity in wind turbines and with current technologies, that coil would cost between AUS$3-5 million to manufacture. The same length of magnesium diboride superconducting coil costs AUS$180,000 and that figure could reduce dramatically as magnesium diboride becomes less and less expensive.

Hyper Tech Research magnesium diboride coil is about AUS$1 per meter to manufacture.

A magnesium diboride superconducting coil can replace the gear box. This will capture the wind energy and convert it into electricity without any power loss, and will reduce manufacturing and maintenance costs by two thirds. When an electric current is sent into a conduction loop made of conventional copper wire, about 7-10 per cent of this energy is lost due to resistance. The wire heats up and decays quickly. However, if a superconducting material is used, the current will circulate indefinitely even after the power is turned off..

An MgB2 superconducting direct drive generator will minimize tower size and weight by substituting heavy iron with lightweight composites and will increase the power density of the wind turbine. Equipment reliability increases because of a more simplistic generator rotor design. Another advantage of using MgB2 generators for offshore projects is that the unit could be repaired onsite without being removed from the structure.

MgB2 wires





Properties depend greatly on composition and fabrication process. Many properties are anisotropic due to the layered structure. 'Dirty' samples, e.g., with oxides at the crystal boundaries, are different from 'clean' samples.[8]
The highest superconducting transition temperature Tc is 39 K.
MgB2 is a type-II superconductor, i.e. increasing magnetic field gradually penetrates into it.
Maximum critical current (Jc) is:
10^5 A/m2 at 20 Telsa,
10^6 A/m2 at 18 Tesla,
10^7 A/m2 at 15 Telsa,
10^8 A/m2 at 10 Tesla,
10^9 A/m2 at 5 Tesla

As of 2008 :
Upper critical field (Hc2):
(parallel to ab planes) is ~14.8 Tesla,
(perpendicular to ab planes) ~3.3 T,
in thin films up to 74 T,
in fibers up to 55 T

Improvement by doping

Various means of doping MgB2 with carbon (e.g. using 10% malic acid) can improve the upper critical field and the maximum current density (also with polyvinyl acetate).

5% doping with carbon can raise Hc2 from 16 T to 36 T whilst lowering Tc only from 39 K to 34 K. The maximum critical current (Jc) is reduced, but doping with TiB2 can reduce the decrease. (Doping MgB2 with Ti is patented.)

The maximum critical current (Jc) in magnetic field is enhanced greatly (approx double at 4.2 K) by doping with ZrB2.

Even small amounts of doping lead both bands into the type II regime and so no semi-Meissner state may be expected.

European Union and Australia are working on MgB2 for large Wind Turbines

A superconducting direct drive generator based on field windings of MgB2 superconducting tape is proposed as a solution by mounting the generator in front of the blades using a king-pin nacelle design for offshore turbines with power ratings larger than 10 MW as investigated in the INNWIND.EU project.

The target power range of the INNWIND.EU project is 10–20 MW and the loads on a 20MW nacelle of a horizontal axis turbine with a blade diameter reaching 250 meters will be very large. Thus it was investigated if a nacelle design could be found that would be applicable to the entire power range. The 10 MW MgB2 generator can be integrated into a nacelle, which has the potential to be up-scaled towards 20 MW.

Background

121 page dissertation on fabrication of MgB2 and other superconductors Qinyang Wang. Fabrication and superconducting properties of MgB2/Nb/Cu wires with chemical doping by using Powder-In-Tube (PIT) method. Materials Science. Universit´e JosephFourier
- Grenoble I, 2012. English.


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