Computing Implementation of stabilized HTS tape Model based on distribution of currents between the tape layers

Transcription

1 1 Computing Implementation of stabilized HTS tape Model based on distribution of currents between the tape layers Alfredo Álvarez, Pilar Suárez, Belén Pérez and João Murta-Pina "Benito Mahedero" Group of Electrical Application of Superconductors University of Extremadura 6th International Workshop on Numerical Modelling of HTS /Costa de Caparica

2 2 Universidade Nova Lisboa Engineering School BADAJOZ

3 3 The problem of superconducting elements to be modeled is the nonlinearity of their response, due to the nonlinearity of the superconductor which the elements are made of. J c Current Density (J) Superconducting interior volume Critical Surface Minimum radius of curvature B c T c Temperature (T) Magnétic field (B) Liquid Nitrogen 77 K=-196,15ºC Tape 6th International Workshop on Numerical Modelling of HTS /Costa de Caparica

4 Hypothesis for an Engineering model of the superconducting tape 1. Current peak values, Ip, can exceed the critical current Ic. 2. The excess current over Ic flows through the stabilizing layers. 3. The superconducting layer maintains the current at its critical value. 4. When Ip < Ic, the whole current flows through the superconducting layer. 4

5 5 Engineering model of the superconducting tape i S i T : Whole current in the tape i T i YBCO i YBCO : Superconducting layer current v T Equivalent circuit for the proposed hypothesis i S : Resistive stabilizer layer current i T = i YBCO + i S v T =i S R S +L (di/dt) R S L I c n Parameters of the tape i S R S = v YBCO (i YBCO ) Non-linear part of the model 6th International Workshop on Numerical Modelling of HTS /Costa de Caparica

6 Experimental tests 6 Pressure A. DC Characteristic I = 99.5A n = 23.5 c HTS tape CHARACTERISTICS OF THE TAPE Manufacturer SuperPower Inc. Critical current K 77 K Type Labview SCS4050i-AP apllication control Width 4 mm Superconductor YBCO Thickness 208 μm Stabilizer Copper Stabilizer thick 40 μm I = V Vc I c n V : Voltage in the tape I : Current in the tape I c : Critical current V : Criteria for critical current (1 V / cm) c Vc = 4 V

7 Experimental tests 7 Pressure HTS tape B. Stabilizer Resistance 300 K Labview apllication control R (77 K) = R (300 K) 1 + (77 300) S S Copper layer : Copper temperature coefficient of resistance -1 (typically equal to K ) Rest of the non-superconducting layers in the tape can be neglected

8 Experimental tests 8 Instrumentation amplifier Labview apllication control

9 Experimental tests 9 C. AC Characteristic i-v characteristics of the tape, transporting 50 Hz sinusoidal current with amplitude increasing from 20 A-peak to 130 A-peak. D. Induction Coefficient L 1 V p = 2 f I p L= H 7 L = H / m

10 Model 10 D. Superconductor Nonlinear Drop Voltage i T i S v YBCO i YBCO v T v YBCO =v T - L (di/dt) I TP > I c I TP < I c

11 I TP > I c i T Model E. Stabilizer Layer Current i S = i T (t) Ic > 0 i S Effective resistance R S I TP > I c In phase I TP > I c 11 iybco=ic R S = V YBCOp /I Sp I Sp =I Tp Ic CHARACTERISTICS OF THE STABILIZER LAYER Reference quantity 130 A 125 A 120 A 110 A I Tp Ic Excess current (A) Peak voltage (mv) Eff. resistance (μω) In phase I TP < I c I TP < I c I TP < I c i S just the necessary for verifying i S R S = v YBCO i T i S iybco<ic

12 12 Model G. YBCO Layer Current i T i S i YBCO v T Equivalent circuit for the proposed hypothesis i YBCO = i T - i S Sinusoidal current in the tape is Somehow limited in the YBCO layer at the critical current value 6th International Workshop on Numerical Modelling of HTS /Costa de Caparica

13 13 BASIC COMPUTER MODEL Simulink i T i S i YBCO v L v T v YBCO

14 14 Conclusions An engineering model of a superconducting tape can be done from simple experimental parameters A more deep study of the stabilizer resistance is carried out. The study of the thermal behavior for transition is needed. The study of the external magnetic field for complex element is needed. Thank you for your attention Alfredo Álvarez, Pilar Suárez, Belén Pérez and João Murta-Pina