Large power direct drive superconducting generators for off-shore wind turbines show promise for competitive cost of energy and would enable the deployment of wind turbine outputting 10 MW or more. As part of an ARPA-e project, a 10 MW generator was optimized based on YBCO excitation coils. The rotor is using an iron core in order to reduce the amount of HTS required and lead to an acceptable cost of energy. A subscale HTS coil was fabricated using off-the-shelf YBCO tapes as a demonstrator. This paper deals with the testing of the HTS coil between 77 K and 25 K. The coil is 0.65 meter long and 0.32 meter wide. It is composed of about 100 m of YBCO tape from Superpower. The coil is conduction cooled using an AL325 cryocooler; the experimental setup will be described in detailed as well as the electromagnetic and thermal analysis of the coil. The experimental results consist in Ic measurements at different temperature and voltage monitoring of the 4 sections of the coil to identify and potential conductor motion of mechanical structure degradation.

This work was partially supported by ARPA-e

Superconducting MgB2 coils have a promising application niche in large wind generators. The potential implementation as field coils involves machines with smaller size and reduced weight, which is the real benefit compared to conventional non-superconducting alternatives. This is a key factor, especially in offshore wind turbines above 10 MW, where wind market demands higher power rate and more compact turbines in order to optimize capital and operational costs.
Under the SUPRAPOWER project, a 10 MW direct drive wind generator concept will be probed through an experimental validator, where superconductivity is implemented in rotating DC coils. For the required operational temperature, current density and magnetic field, the available commercial MgB2 wire has been selected. It is cheaper and better suited than other solutions as 1G and 2G HTS.
The aim of the present work is to analyse the operational conditions of MgB2 DC field coils, cooled by a cryogen-free system and developed according the required performance of the SUPRAPOWER generator. The paper deals with the design, manufacturing and experimental results of full scale superconducting coils.

The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under SUPRAPOWER project, grant agreement n° 308793.

Optimization Study of Machine Parameters for 10 MW Salient-pole HTS Wind Turbine Generators
Yuanyuan Xu, Naoki Maki, Mitsuru Izumi
Large-scale wind turbine high temperature superconducting (HTS) synchronous generators (WTHGs), which can directly meet the wind power systems under low speeds and have great merits such as lighter weight, higher power density and higher efficiency than the conventional counterparts due to HTS carrying high current density. A conceptual structure of a salient-pole WTHG was proposed in the previous work, which has both rotor and stator iron cores considering the cost-performance and the light weight, and a novel electrical design method for the WTHG was introduced [1]. In the present paper, the electrical designs of 10 MW salient-pole WTHGs with different stator outer diameters are conducted. Some main machine parameters such as the pole pitch, the number of poles, the electric loading, and the magnetic flux density in rotor irons of 10 MW WTHGs with different stator outer diameters are optimized and determined considering the generator weight, HTS length and the generator efficiency, respectively. Then, the influence of the stator outer diameter on the generator performance is made clear, and the optimized design results of 10 MW WTHGs with different stator outer diameters are studied comparatively.
[1] Y. Xu, N. Maki, and M. Izumi, “Electrical Design Study of 10 MW Salient-pole Wind Turbine HTS Synchronous Generators,” IEEE Trans. Appl. Supercond, vol. 24, no. 6, Art. ID 5202706, Dec. 2014.

Recently, gearless type wind power generators, which have very low rotation speed and high torque, have been preferred over the geared type due to the gearbox reliability. Because the gearless generator becomes very large and heavy, many companies have tried to develop a wind power generator with larger capacity, smaller size and lighter weight. A high-temperature superconducting (HTS) generators could be a key technology to solve the weight and size issues. However, the HTS generator has some drawbacks such as low vacuum level and long cool-down time of the cooling system and power loss from the DC power supply, slip ring and copper current lead for power supply. This paper deals with the modularization of a large-scale HTS generator including individual cryo-cooling system and flux pump to solve the cooling and power loss problems. The modularization of the HTS generator means each HTS pole magnet has one cryo-cooler and one flux pump individually. The cryo-coolers cool-down the HTS pole magnets, and the flux pumps flow the field current to the magnet without the DC power supply, cooper current lead, and slip ring. The flux pump is attached on the surface of the cryostat, which rotates by rotatory power of the generator rotor parts. The rotating flux pump induces DC current flowing to the HTS pole magnet by the time varying magnetic field. The conceptual design of the modularized large-scale HTS generator is designed by using 3D CAD program. Moreover, when modularized one HTS pole magnet has break down, the output characteristics of the HTS generator is analyzed using by 3D FEM program. As the results, the large-scale HTS generator is modularized including the cryo-cooling system and flux pump. Compared to the normal condition of the HTS generator, the output power of the fault condition of the HTS pole magnet is reduced. However, the decrease of the output power does not lead to any problems, and it can be compensated by using output power control of the back-to-back converter. Therefore, the modularized HTS generator has higher reliability than general HTS generators. This modularization of the HTS generator can be effectively utilized to design a large-scale HTS generator for wind turbine.

This work was supported by the Power Generation & Electricity Delivery Core Technology Program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP), granted financial resource from the Ministry of Trade, Industry & Energy, Republic of Korea. (No. 20142020103560)

Superconducting motors have been in the scope of research for several decades but the complexity of Cryogenics for Low Temperature Superconductors (LTS), and the global cost, did not allow the leap to the necessary readiness level for standard use in both large power motors and in low power level neither. The appearance of new High Temperature Superconductors (HTS) renewed these research activities to all laboratories active in superconducting applications in the search of new market niches, mixed copper-HTS , permanent magnet-HTS wires, HTS wires and bulks, and a large etcetera of creative devices, always with the aim of taking profit of the large magnetic field and efficiency that can be expected.
The high level of development achieved by the HTS materials and, specifically by the, ReBCO family, and the growing number of manufacturers expected, has led to the simplification of the so called trapped field type of HTS motors by substituting the brittle and expensive bulks by stacks of thin tapes able to trap a high amount of magnetic flux in a reasonably area. In this way the mechanical properties of the superconducting block are largely improved at a lower cost, and an easy implementation in the standard topologies of the motors.
We describe the concept, the design and the experimental implementation of a Stacks-Wire Based Superconducting motor made in the way for optimizing the ratio power/ weight. Details of cooling, magnetization, performances and cost are also considered.

Authors would like to recognize the support of EU-FP7 NMP-LA-2012-280432 EUROTAPES project and Spanish MAT2011-28874-C02 national project

The construction and the tests of a superconducting machine using high and low temperature superconductors are described. The originality of the prototype concerns the design of the inductor.
The inductor is composed of two coaxial superconducting solenoids made with NbTi wires separated by an YBCO superconducting plate . Both solenoids are fed by a direct current and each of them produces a magnetic field in the same direction.
An inclined superconducting bulk is placed between the two solenoids. It is used as superconducting magnetic barrier. The diamagnetic behavior of a superconducting bulk cooled under zero-field is used to obtain a variation of the magnetic flux density in the air-gap. This kind of inductor is original.
The superconducting motor consists of a 3-phase stator with copper windings and this new kind of inductor. This motor have been designed by 3D finite element computations. After this design, this motor have been built and tested.
The inductor has been immerged in a cryostat and cooled at 4.2 K in liquid Helium. Several tests have been carried out as follows
No-load and short-circuit tests allowed us to determine the equivalent circuit parameters,
Load tests in generator mode at rated conditions.
Most of the measured external quantities have been checked by 3D finite element computations.

This paper summarizes results from testing of Guina’s 200 kW experimental homopolar electromagnetic turbine. Our experimental machine is the first machine that uses state-of-the-art high field superconducting magnet and liquid metal current collector (LMCC) technology. These technologies are very important in achieving high and stable machine performance. The magnet system, which produces a DC magnetic field, consists of a pair of superconducting magnets in a spilt coil design. Each magnet has a mirror-inverted coil arrangement of one main coil and two cancelling coils. The cancelling coils are a Guina invention that reduces the magnetic field below 200 mT in the field critical sliding contact area. The main coils, made of 1G HTS wire, have a maximum design field of 2.7 Tesla at 26 Kelvin. The average working field seen by the rotor is above 1 Tesla. A new 40,000 Amp LMCC was developed in-house to ensure a low resistance, reliable and high speed electrical contact between the stator and rotor. The sodium-potassium LMCC allows stable electrical contact between the rotor and stator at surface speeds up to 100 m/s with current densities up to 250 A/cm². The copper rotor and LMCC system are fully enclosed within an air-tight composite envelope to maintain an inert atmosphere and prevent oxidisation of the liquid metal.
The critical components were tested separately and under a variety of conditions to ensure their stable operation under various loads. The motor performance curve was determinate over a wide range of speeds and torques. Behaviour at starting, overload and during rapid load changes was studied and analysed. This paper summarizes the development process, the testing of different subcomponents and the full load testing of the machine. Finally, we would like to present a future outlook for our prototype design that considers power-to-weight, size, efficiency and environmental influence of our electromagnetic turbines.