The EPEC Superconductivity Group –Engineering Department - University of Cambridge www2.eng.cam.ac.uk/~tac1000 1

Superconducting Fault

Current Limiters A. V. Velichko, T. A. Coombs

Department of Engineering, Cambridge University, UK.

Funded by EPSRC

The EPEC Superconductivity Group –Engineering Department - University of Cambridge www2.eng.cam.ac.uk/~tac1000 2

Outline

Overview of the work done Physical Background and Modelling Simulation and Experiment Summary and Future Plans

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Overview

FCLs are highly nonlinear devices, extensive simulation is required:

So far we have addressed:- High-aspect ratio - Multi-element configuration- First Experiments (DC VACH, AC loss and Pulse Measurements)

Problems remaining to solve:- Structural deformations (simulation and experiment) - Overall contribution to the power network.

Problems to be solved within the project:

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Physical Background and Modelling (I)

SingleFCL

Structural

ThermalElectrical

All Properties are NONLINEAR

and INTERDEPENDENT!

If done consistently & simultaneously –

very time-consuming and could be fallible

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Physical Background and Modelling (II)

EXISTING PROPRIETARY MODEL

From Experiment: - Spread in Ic and n; Strain and Stress;

Model takes into account:Thermal and Electrical;

Need to incorporate: Structural, Multi-element

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Physical Background and Modelling (III)

• 3D model• Accounts for Inhomogeneities • Proper thermal boundary conditions• Linked Electrical and Thermal Properties• External Elements

Nitrogen boil-off

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Simulation (I)

We also use commercial FEM software (FEMLAB) to:

- Verify the proprietary model- Simulate other features (Structural modelling)- Quick test for new geometries

So far we have used Femlab to:

• Verify T and I –distribution for metals • Estimate importance of metallic substrate• Check the concept of the length scaling

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Simulation: verifying our model (II)FCLSimu2003D & FEMLAB

Cu-block, 1*0.5*0.25 mm3, takes ~ 1 minute on P-IV, 2.4 GHz, 512 MGb RAM

T = 275.24-275.3 K T = 260.24-260.27 K

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Simulation: effect of substrate (III)

Ni (5-50 m)-CeO2(0.5 m)-YBCO(1.0 m)-Ag (10 m) over 1 sec, Q=10*(1+2*t), (2D, 3554 cells, 372 boundary elements)

Multilayer Ni/CeO2/YBCO/Ag, ~ 2 minutes on P-IV, 2.4 GHz, 512 MGb RAM

Ni-5m Ni-25m Ni-50m

FCLSimu2003D

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Simulation: size-multipliers (IV)

T = 266.62-266.64 KScaled Up by 10

T = 266.67-266.68 K

Unscaled, Cu, 1*0.5*0.1 mm3

T = 265.5-267.5 K

Scaled Down by 10

FCLSimu2003D

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Simulation: size-multipliers (V)

BSCCO, Unscaled,6*5*0.5 mm3

BSCCO, Scaled Up by 1000 to 6*5*0.5 mm3

BSCCO, Scaled down by 0.001 to 6*5*0.5 mm3

T = 80.8-81.9 K T = 80.8-81.9 K T = 80.8-81.9 K

FCLSimu2003D

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Simulation: multi-element (VI)FCLSimu2003D

Two uniform elements in parallel, YBCO, 200*40*25 m3 each

YBCO: T = 150.1-150.7 K

N-gas

YBCO

YBCO

Layout

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Simulation: multi-element + defect (VII)

Two elements in parallel, one with defect YBCO, 200*40*25 m3 each

YBCO: T = 106.7-106.8 K

N-gas

YBCO

YBCO

YBCO: T = 175.1-176.1 K

Layout

FCLSimu2003D

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Experiments – DC VACH (I)

dc Current-Voltage characteristics,4 consecutive runs

YBCO tape, dc IV-characteristics, 7/03/2006

I, A

0 20 40 60 80 100 120 140 160

U,

V

0.0

5.0e-6

1.0e-5

1.5e-5

2.0e-5

2.5e-5

1st run2nd run3rd run4th run

DC in-phase Voltage vs. Current for LANL YBCO tape No.1, 7.03.06

I, A

0 20 40 60 80 100 120 140 160

DC

Vo

ltag

e (V

)

-5.0e-6

0.0

5.0e-6

1.0e-5

1.5e-5

2.0e-5

2.5e-5

Vc*(I/Ic)^nVdc

Fitting dc Current-Voltage Characteristic with EJ-model

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Experiments, AC Pulses (II)

AC Pulse measurements, 25% Vmains

Pulse measurements (2 pulses, 25% V_mains) on YBCO tape No.1, 7.03.06

time, sec

0.07 0.08 0.09 0.10 0.11 0.12

I ac, A

-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

0.06

Ua

c, V

-0.04

-0.02

0.00

0.02

0.04CurrentVoltage

Pulse measurements (2 pulses, 30% V_mains) on YBCO tape No.1, 7.03.06

time, sec

0.07 0.08 0.09 0.10 0.11 0.12

Ia

c,

A

-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

0.06

0.08

Ua

c, V

-0.08

-0.06

-0.04

-0.02

0.00

0.02

0.04

0.06

0.08

0.10

CurrentVoltage

AC Pulse measurements, 30% Vmains

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Experiments, AC Pulses (III)

AC Pulse measurements, 6 pulses45% Vmains, expanded

Pulse measurements (2 pulses, 45% V_mains) on YBCO tape

time, sec

0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20

Ia

c,

A

-0.15

-0.10

-0.05

0.00

0.05

0.10

0.15

Ua

c,

V

-3

-2

-1

0

1

2

3

CurrentVoltage

Pulse measurements (2 pulses, 45% V_mains) on YBCO tape, expanded

time, sec

0.04 0.05 0.06 0.07 0.08

I ac, A

-0.10

-0.05

0.00

0.05

0.10

Ua

c, V

-2

-1

0

1

2

CurrentVoltage

AC Pulse measurements, 6 pulses45% Vmains, full scale

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Summary and Future Plans

So far we have:• Estimated Substrate effect• Verified proprietary software in FEMLAB• Solved high-aspect ratio problem• Attempted simulation of multi-element geometry• Performed first experiments: DC, AC loss & pulse

In the near future we plan to:• Input realistic parameters (n and Jc) into the EJ-model• Continue with multi-element model (target - YBCO tape)• Simulate Structural Modifications• Complete Electrical Network• Further experiments: IV-characteristics, stress & strain

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Project Schedule (original)Activity Year 1 Year 2 Year 3

Multi-Element Model

Structural Failure

Modelling of Complete Electrical System

Measurement

Validation

Project months 3 6 9 15 18 21 27 30 33

Mastered existing FCL modelCreated 2D Thermal model in FEMLAB

Repeat Existing model in Femlab & Built multi-element model

Setting up Experiments & Making Measurements

Building Structural Model

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Project Schedule (reviewed)Activity Year 1 Year 2 Year 3

Multi-Element Model

Structural Failure

Modelling of Complete Electrical System

Measurement

Validation

Project months 3 6 9 15 18 21 27 30 33

Estimated Substrate effectSolved high aspect-ratio problemVerified Existing model in Femlab & Built multi-element model

Setting up Experiments& Making Measurements

Building & verifying Structural Model