We have examined the potential of 10 MW superconducting direct drive generators to enter the European offshore wind power market and estimated that the production of about 1200 superconducting turbines until 2030 would correspond to 10% of the EU offshore market. The expected properties of future offshore turbines of 8 and 10 MW have been determined from an up-scaling of an existing 5 MW turbine and the necessary properties of the superconducting drive train are discussed. We have found that the absence of the gear box is the main benefit and the reduced weight and size is secondary. However, the main challenge of the superconducting direct drive technology is to prove that the reliability is superior to the alternative drive trains based on gearboxes or permanent magnets. A strategy of successive testing of superconducting direct drive trains in real wind turbines of 10 kW, 100 kW, 1 MW and 10 MW is suggested to secure the accumulation of reliability experience. Finally, the quantities of high temperature superconducting tape needed for a 10 kW and an extreme high field 10 MW generator are found to be 7.5 km and 1500 km, respectively. A more realistic estimate is 200–300 km of tape per 10 MW generator and it is concluded that the present production capacity of coated conductors must be increased by a factor of 36 by 2020, resulting in a ten times lower price of the tape in order to reach a realistic price level for the superconducting drive train. (Some figures in this article are in colour only in the electronic version)

Superconducting Wind Turbine Generators

Canted-Cosine-Theta (CCT) magnet is an accelerator magnet that superposes fields of nested and tilted solenoids that are oppositely canted. The current distribution of any canted layer generates a pure harmonic field as well as a solenoid field that can be cancelled with a similar but oppositely canted layer. The concept places windings within mandrel's ribs and spars that simultaneously intercept and guide Lorentz forces of each turn to prevent stress accumulation. With respect to other designs, the need for pre-stress in this concept is reduced by an order of magnitude making it highly compatible with the use of strain sensitive superconductors such as Nb3Sn or HTS. Intercepting large Lorentz forces is of particular interest in magnets with large bores and high field accelerator magnets like the one foreseen in the future high energy upgrade of the LHC. This paper describes the CCT concept and reports on the construction of CCT1 a “proof of principle” dipole.

/pdf/canted-cosine-theta-magnet-cct-a-concept-for-high-field-hj1d6wb5gy.pdf

Canted–Cosine–Theta Magnet (CCT)—A Concept for High Field Accelerator Magnets

Author(s): Wang, X; Caspi, S; Dietderich, DR; Ghiorso, WB; Gourlay, SA; Higley, HC; Lin, A; Prestemon, SO; Van Der Laan, D; Weiss, JD | Abstract: REBCO coated conductors maintain a high engineering current density above 16 T at 4.2 K. That fact will significantly impact markets of various magnet applications including high-field magnets for high-energy physics and fusion reactors. One of the main challenges for the high-field accelerator magnet is the use of multi-tape REBCO cables with high engineering current density in magnet development. Several approaches developing high-field accelerator magnets using REBCO cables are demonstrated. In this paper, we introduce an alternative concept based on the canted cos θ (CCT) magnet design using conductor on round core (CORC®) wires that are wound from multiple REBCO tapes with a Cu core. We report the development and test of double-layer three-turn CCT dipole magnets using CORC® wires at 77 and 4.2 K. The scalability of the CCT design allowed us to effectively develop and demonstrate important magnet technology features such as coil design, winding, joints and testing with minimum conductor lengths. The test results showed that the CCT dipole magnet using CORC® wires was a viable option in developing a REBCO accelerator magnet. One of the critical development needs is to increase the engineering current density of the 3.7 mm diameter CORC® wire to 540 A mm-2 at 21 T, 4.2 K and to reduce the bending radius to 15 mm. This would enable a compact REBCO dipole insert magnet to generate a 5 T field in a background field of 16 T at 4.2 K.

/pdf/a-viable-dipole-magnet-concept-with-rebco-corc-wires-and-2ioqox99ug.pdf

A viable dipole magnet concept with REBCO CORC® wires and further development needs for high-field magnet applications

In this paper, the commercial activities in the field of superconducting machines, particularly superconducting wind turbine generators, are reviewed and presented. Superconducting generators have the potential to provide a compact and light weight drive train at high torques and slow rotational speeds, because high magnetic fields can be produced by coils with very little loss. Three different superconducting wind turbine generator topologies have been proposed by three different companies. One is based on low temperature superconductors; one is based on high temperature superconductors; and one is a fully superconducting generator based on MgB2. It is concluded that there is large commercial interest in superconducting machines, with an increasing patenting activity. Such generators are, however, not without their challenges. The superconductors have to be cooled down to somewhere between 4 K and 50 K, depending on what type of superconductor is employed, which poses a significant challenge both from a construction and operation point of view. The high temperature superconductors can facilitate a higher operation temperature and simplified cooling, but the current price and production volumes prohibit a large scale impact on the wind sector. The low temperature superconductors are readily available, but will need more sophisticated cooling. Eventually the Cost of Energy from superconducting wind turbines, with particular emphasis on reliability, will determine if they become feasible or not and for such investigations large-scale demonstrations will be needed.

/pdf/development-of-superconducting-wind-turbine-generators-12kqww9uln.pdf

Development of Superconducting Wind Turbine Generators

/pdf/development-of-superconducting-wind-turbine-generators-4s4ty9jscs.pdf

Development of superconducting wind turbine generators

We describe a new technology for superconducting dipoles that has significant advantages for use in particle accelerators. The dipole field is obtained by using concentric pairs of helically-wound coils that are tilted at opposite angles; this effectively cancels the solenoid component of the field and adds the dipole content of each layer. This coil configuration produces a dipole field with systematic errors <10/sup -8/ of the main field in 85% of the coil aperture. We show, using a design example, how many of the inherent problems with the traditional cosine theta type of coil are eliminated and the cost of development and manufacturing the magnets is substantially reduced.

The double-helix dipole - a novel approach to accelerator magnet design

We describe a new technology for superconducting quadrupole magnets especially for use in particle accelerators. The principle is based on the application of a sinusoidal modulation to the axial positions of the conductor windings in solenoids. The method can also be employed to produce higher-order multipole fields. Due to their solenoid-like geometry, these coils are significantly simpler to manufacture than standard (racetrack) cosine-2-theta coils and have significantly smaller systematic field errors without using any field-shaping spacers. When two complementary coil layers (with opposite current flow) are combined, the solenoid components of the fields are cancelled and the quadrupole or higher-order fields add. An example of such a design is described which generates a gradient of 130 T/m with systematic errors less than 10/sup -8/ at 67% of the aperture.

Modulated double-helix quadrupole magnets

We describe a technology for creating easy-to- manufacture combined function magnets. The field is produced by double-helix coils in which the axial path of the windings is defined by a sinusoidal function containing the superposition of the desired multipoles. The result is a magnet that can contain, for example, a pure dipole field with superimposed multipole fields whose magnitude relative to the dipole field can be easily controlled to any level. We show how low level (i.e. 0.1%-1%) modulation amplitudes of the superimposed multipoles can be used as built-in or "free" correction coils to compensate for iron saturation effects or geometrically-induced multipoles. The combined function winding can also be used to superimpose a dipole and quadrupole winding where the quadrupole integral of Gdl can be adjusted to any level desired over the length of the main dipole magnet. In this way a "free" quadrupole can be obtained within a dipole. The characteristics of this type of combined function magnet are also discussed.

Combined function magnets using double-helix coils

The double-helix dipole configuration, which uses concentric pairs of oppositely-tilted helical windings to generate a dipole field, is the basis of a design for a unique high-torque, low-rpm, compact superconducting motor. We describe an analysis method that uses coupled mutually-inductive equivalent circuits for each phase for computing the performance and operating characteristics of such a device. We discuss the performance and limitations of an example motor that uses NbTi superconducting cables for the stator and rotor. The example device is a 4-pole, 2-phase induction motor that produces typically 10 000 HP for a 1-m effective length rotor with a 0.4 m diameter rotor operating at /spl sim/300 rpm. In addition, the relatively large minimum bend radius of the double-helix coil configuration also facilitates the use of brittle superconducting materials such as HTS or A-15 for this application.

A superconducting induction motor using double-helix dipole coils

This paper illustrates the use of a simple interactive magnetic field calculator (IMC) program to estimate field strength and allowed harmonics for cosine theta dipole or quadrupole magnets. Niobium-tin coil designs from Saclay and the University of Twente are used as examples, and the IMC results are compared with the values from the magnet designers.

/pdf/interactive-procedure-for-rapid-performance-estimates-of-4ga9vg7vwk.pdf

M.J. Ball

Papers

The double-helix dipole - a novel approach to accelerator magnet design

Modulated double-helix quadrupole magnets

Combined function magnets using double-helix coils

A superconducting induction motor using double-helix dipole coils

Interactive procedure for rapid performance estimates of magnet designs