Upgrading electric power quality by superconducting flywheels

PHYSICA Physica C 341-348 (2000) 2609-2610

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Upgrading Electric Power Quality by SuperconductingFlywheels Istv/m Vajdaa, Tam,is Porjesz% Attila Gy/Srea, Andr~is Szalayc, Wolfgang Gawalekd aDept of Electrical Machines and Drives, Budapest University of Technology and Economics, Egry J6zsef utca 18, H- 1111 Budapest, Hungary* bDept of General Physics, E6tv6s University, Budapest, Hungary P~izm/my P6ter s6tfiny 1, H-1111 Budapest, Hungary cS-Metalltech, Ltd, Budapest, T6th L6rinc utca 11, H- 1122 Budapest, Hungary qPHT Jena, Helmholzweg 4, D-07743, Jena, Germany An experimental flywheel based on high temperature superconductors was constructed. The aim of the study is to investigate the possible use of this technology to improve electric power quality against voltage disturbances. Some preliminary results on the flywheel performance are reported. 1.

INTRODUCTION

Brownouts or blackouts of electrical power may result in very high costs fi)r sensitive consumers.

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Superconducting energy storage can offer technically viable and economically beneficial solutions to such power quality problems [1,2]. The case of using a high-To superconductor (HTS) flywheel is discussed below.

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Figure 1. Cross section of the flywheel. 1-stator, 2-rotor, 3-PM, 4-HTS ring, 5-LN:, 6- LN2 container, 7-base plate, 8-rotor cup, 9-stator core, 10-stator winding.

Figure 21 Photograph of the flywheel.

* This work was supported by OTKA T022513, FKFP 0247/97. 0921-4534/00/$ - see front matter © 2000 Elsevier Science B.M Pll S0921-4534(00)01380-0

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/. Vaida et al./Physica C 341-348 (2000) 2609-2610

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Figure 3. Maximum stored energy versus the thickness to height aspect ratio, k k The graphs represent rings with different inner and outer radii, where their ratio ranges from 6 = O. 1 (lower) to 0.7 (upper). 2.

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EXPERIMENTAL FLYWHEEL

A cross sectional view of the experimental HTS flywheel is shown in Figure 1, while a photograph of it is displayed in Figure 2. The design integrates the rotor body (flywheel) with the motor and generator units. The generator is not shown in the figures. The rotor incorporates an aluminum cylinder (cup) driven by a rotating magnetic field generated by the stator winding. The stabilization of the shaft was improved by introducing a small HTS/PM coupling at the top of the rotor. The HTS levitator is cooled down in the presence of a magnetic field (field cooling). The main data of the experimental flywheel are the following: The levitator is a melt-processed YBCO ring of dimensions O43/~ 15mmx 15mm and a disk of size O25.4mmx 15mm serves as stabilizer. The permanent magnets are ring shaped and made of NdBFe. The flywheel has a mass of 1.806 kg, maximum speed of 500 rpm, and can store energies up to 11.85 J. The spin-down time without a vacuum chamber has been measured to exceed 58 minutes. The present flywheel represents an intermediate stage towards a targeted device. A design algorithm has already been developed in order to predict the performance of flywheels [3]. Figure 3 shows the calculated maximum stored energy Em~-, as function of the aspect ratio kh between the thickness and

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Figure 4. Maximum stored energy versus inner-toouter radius ratio 5 for kk = 0.5, 1 and 2. height of the HTS ring. Figure 4 shows how E,,,,~, depends on the radius ratio, 5, of the inner and outer ring radii. The plots are obtained for a reference case of a 1 kg mass and a speed of 10,000 rpm. The calculated energy storage capacity of the present flywheel running at 10,000 rpm equals 2.48 kJ. We hope to achieve such performance in the near future.

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CONCLUSIONS

An HTS flywheel has been constructed. The design includes a disk-type motor/generator unit with a low-loss magnetic core and with one single semiconductor current converter which proved to reduce radial forces, stand-by losses as well as the costs. At the same time an increased efficiency and reliability could be obtained. ACKNOWLEDGEMENT The authors express their gratitude to Prof. Kamel Salama for providing excellent HTS parts. REFERENCES 1. 2. 3.

I. Vajda, T. Porjesz, A. Szalay, J. Lukfics, ISEM, Pavia, May 1999 (in print) J.R. Hull, IEEE Spectrum 34 (1997), pp. 20-25 I. Vajda and L. Moh~icsi, IEEE Trans. Applied Superconductivity 7 (1997), pp. 916-919