Resistive SCFCL

8/3/2019 Resistive SCFCL

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Thesis 1

RESISTIVE SUPERCONDUCTING

FAULT CURRENT LIMITER


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Contribution of this Thesis

Simulations Simulations were carried out on the resistive

SCFCL in order better to understand its

minimise the problems facing it. Simulations

of the shielded-inductive SCFCL were also

carried out in order to aid comparisons

between it and the resistive SCFCL.

The simulations:


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1. Enabled design trade-offs for the resistive SCFCLto be established on a quantitative basisbetween the length and the critical currentdensity of the superconducting film, the type ofsu s ra e ma er a , e va ue o e app evoltage per unit length across the film, and theperformance of the resistive SCFCL.

2. Enabled the impact of a shunt resistor on the

reduction of transient overvoltages in theresistive SCFCL to be evaluated.


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3. Showed how the weak parts problem in the

resistive SCFCL could be reduced or eliminated by

increasing the applied voltage per unit length across

the superconducting film, by the application of an

externally magnetic field on the film from a shunt orseries connected boost coil, and by using a high

thermal conductivity substrate such as sapphire.

4. Enabled design trade-offs for the shielded-inductive

SCFCL to be formulated and comparisons to bemade between it and the resistive SCFCL.


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Measurements

Measurements were carried out on a series ofsuperconducting samples under various voltagesand angles of fault occurrence. Measurements

achieved: Superconductor sample with no externally

applied magnetic field.

Superconductor sample with shunt boost coil. Superconductor sample with series boost coil.


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Measurements showed that:

1. The rise in temperature of the superconductor

sample during the fault period can be decreased by

connecting a shunt coil across the sample.

2. Superconductor samples can deal with a highernumber of successive faults when using a shunt

boost coil compared with a series boost coil or no

such a coil.


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3. Transient overvoltages across thesuperconductor sample are higher when a

series boost coil is used.

.

superconducting samples is more likely when

the temperature of the sample is higher than

the critical temperature.


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Sources of Losses in the ResistiveSCFCL: A Critical Review

1. Current Leads: There are two types ofcurrent leads: conventional and

superconducting current leads. There are two

namely, conduction cooled and vapour

cooled current leads.

2. Electric Contacts: The current leads are

connected to the HTSs through electriccontacts.


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Sources of Losses in the ResistiveSCFCL: A Critical Review

3. AC Losses

4. Radiation Losses.

Total Losses: minimum value of the total loss

1.372AI108.5I0.5R0.03787Iq2

csc

-62

ccct +++= l

Costs per year are: 13.63 when using super

insulation material with the bucket, 110.14when using an aluminium bucket and 192.27

when using a brass bucket.


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There is an optimum value of (I L/A) which gives the

minimum value of (QC/I) for each lead system.

Temperature

distribution

along thecurrent lead in

conduction

cooled leads

Temperature

distribution

along the

current lead in

vapour cooled

leads


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(QC/I) versus (I L/A) for both conduction cooledand vapour cooled leads


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Introduction

Behaviour of the resistive SCFCL is determined bythe parameters of the superconducting film suchas length, critical current density, and type ofsuperconducting material.

It is also affected by an externally appliedmagnetic field generated for instance by a seriesor shunt coil, by the type of substrate material onwhich the superconducting film is deposited, and

by the thermal characteristics of the coolingliquid in which the film is immersed.


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Design Parameters of theSuperconducting Film

T < Tc and J > Jc ( ) ( )( )

JJ

77TTT1TJ, c77

c

cksc

=

T > Tc ( )( )90-T1010-8-6

+=sc

tAC

iRT

sc

2

limsc =scl


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Tsc, ilim, Rsc, and vsc for a short superconductingfilm (10cm) when Jc= 10A/mm

2


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Tsc, ilim, Rsc, and vsc for a medium superconductingfilm (50cm) when Jc= 10A/mm

2


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Tsc, ilim, Rsc, and vsc for a long superconductingfilm (10m) when Jc= 10A/mm

2

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Effect of lsc andJc

0

0,2

0,4

0,6

0,8

1

10 20 30 40 50

Firstpeaklimited

current/peak

prospective

current(-)

Jc=10A/mm^2 Jc=100A/mm^2

0

2

4

6

8

10

12

10 20 30 40 50

Fifthpeaklimitedcurrent/peak

nominalcurrent(-)

Length (cm)


Length (cm)

77

127

177

227

277

327

10 20 30 40 50

Tempe

rature(K)

Length (cm)


0

2

4

6

8

10

10 20 30 40 50

Transientovervoltage/peakinput

voltage(-)

Length (cm)


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Effect of the input voltage and Jc

0

0,2

0,4

0,6

0,8

1

40 80 120 160 200

Firstpeaklimitedcurrent/peak

prosp

ectivecurrent(-)

Peak input voltage (cm)


0

2

4

6

8

10

12

40 80 120 160 200

Fifthpe

aklimited

current/peaknominalcurrent

(-)

Peak input voltage (V)


77

177

277

377

477

40 80 120 160 200

Tem

perature(K)

Peak input voltage (V)


0

200400

600

800

1000

1200

1400

10 30 50 70 90 110 130 150 170 190

Peakinputvoltage(V)

Length (cm)


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Tscof the weak and major parts when Jc= 10A/mm2

lsc = 10cm lsc = 60cm

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Tsc of the weak and major parts whenJc = 100A/mm2

lsc = 10cm lsc = 60cm

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Tsc of the weak and major parts when

Jc= 10A/mm2, lsc= 60cm, and Vinp = 160V Jc= 100A/mm

2, lsc= 60cm, and Vinp = 380V

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Tsc of the 10 sections whenJc = 10A/mm2

lsc= 10cmlsc= 60cm

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Tsc of the 10 sections whenJc = 100A/mm2

lsc= 10cm lsc= 60cm


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Conclusion1. Increasing lsc is desirable if instantaneous limitationand recovery with no excessive current dives or

overvoltages are required. However, increasing

increases the volume of the FCL and the losses undernon-fault conditions.

2. IncreasingJc is desirable as this effectively limits the

au curren . owever, or g c, e

superconducting film can survive only if it is so

homogeneous that its whole length quenches

simultaneously.

3. In a long limiter length or in a limiter consisting ofmany samples connected in series, the fault current

may be limited by only a small fraction of the limiter

while most of its length stays below Tc.

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Conclusion4. Increasing the voltage per unit length across the

superconducting film could be a reliable way of

solving the weak parts problem in superconducting

samples with lowJc. However, it is not effective in

samples with highJc.

5. Increasing Tsc during the limiting period is not safeas it is relies on the opening of a circuit breaker to

remove the current. If for any reason the circuit

breaker opening is delayed, the likelihood is that

the superconducting film will be damaged andthere is a consequent risk that the resistive SCFCL

will be totally destroyed.

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Simulation of Resistive SCFCL with

Shunt Resistor and Boost Coils


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Introduction

The first problem can be reduced by

connecting a shunt resistor across thesuperconducting film. The second problemcan be reduced by designing the resistive

SCFCL so that the critical currents of the weakand major parts of the superconducting filmand of the different sections of a multisectionfilm are below the limited current. This could

be done by applying a magnetic field to thesuperconducting film during the fault period.

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Maximum Tsc during the fault period and thenormalised first peak of both ilim and isc whenJc= 10A/mm2 and lsc = 10cm

0,6

0,8

1

227

277

327

ited

pective

e(K)

0

0,2

0,4

77

127

177

0,1 1 10

Firstpeaklim

current/peakpro

current

(-

Temperat

ur

Shunt resistance (ohm)

Tsciscilim

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Waveforms ofvsc

during the fault period for

different Rsh when Jc= 10A/mm2 and lsc =

10cm

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Waveforms of weak part and major part temperaturewhen lsc = 60cm,Jc= 10A/mm

2

Rsh = 0.1 Rsh = 10

The weak parts problem becomes worse when using a shunt resistor

and small values ofRsh are worse than high values. This is becausethe shunt resistor decreases isc, which helps the major part to stay

below the critical temperature, so that the fault is then limited by the

weak part only.

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Effect of Connecting a Shunt Boost

Coil across the Resistive SCFCL

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Superconducting film contains only one smallweak part

Jc= 100A/mm2Jc= 10A/mm

2

The weak parts problem is diminished when a magnetic

field is applied from a shunt boost coil. However, the

problem still exists, especially with highJc.

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Multisection superconducting film

Jc= 10A/mm2 and lsc = 60 cm Jc= 100A/mm

2 and lsc = 10 cm

The problem is nearly solved. However, a higher magneticfield would be required to quench all 10 sections.

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Effect of Connecting a Series Boost

Coil with the Resistive SCFCL

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Values ofKc, Lseries and Rseries of theseries boost coil

Values ofKc and the corresponding impedancesof the coil estimated for six designs of boost coil

same core different number of turns .

Kc (T/A) 0.0125 0.01 0.005 0.0025 0.002 0.001

L (mH) 1.7 1.088 0.272 0.068 0.04352 0.01088

R (m) 34 27.2 13.6 6.8 5.44 2.72

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Superconducting film contains only one small weakpart forJc = 10A/mm

2, lsc = 60cm, and Kc = 0.002T/A

With this small value ofKc, the two parts quenchsimultaneously, however, the above design is accompanied

by high overvoltages ofvsc


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Multisection superconducting film

Jc

= 10A/mm2,

= 60cm

Jc

= 100A/mm2,

= 10cm

Jc

= 100A/mm2,

= 60cm

Q NQ Q NQ Q NQ

Without boost coil 3 7 7 3 1 9

With shunt boost coil

(perpendicular field)

8 2 9 1 1 9

Kc = 0.0125T/A

With series boost coil

(Parallel field)

9 1 10 0 10 0

Kc = 0.002T/A Kc = 0.001T/A Kc = 0.01T/A

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Conclusion

1. Use of a shunt resistor is advantageous with high

Jc but cannot be used with lowJc films. Low valuesofRsh are not preferred. Transient overvoltages

can be reduced by using a shunt resistor.

2. Use of a shunt boost coil is accompanied bysignificant transient overvoltages. Perpendicular

magnetic field is preferred when a shunt boost

coil is used. It helps to reduce the weak parts

problems but seems not to solve it completely.Finally, large coils are required to generate high

magnetic fields.

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Simulation of Resistive SCFCL

with Different Substrates

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Introduction There are several substrates available and several

deposition methods for HTS. LaAlO3 (Lanthanum

Aluminate), Al2O3 (Sapphire), YSZ (Yttria StabilisedZirconia), STO (Strontium Titanate), and MgO

(Magnesium Oxide) substrates are used for YBCO films.

e erma con uc v y o e su s ra e p ays a grea

role in the removal of heat from the superconductingfilm during the fault period.

If the superconducting film is deposited on a low

thermal conductivity substrate then the heat removedto the substrate will be small. However, if a high

conductivity substrate was used then the heat removed

will be improved.

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Heat transfer between thesuperconducting film and liquid nitrogen

+=


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Heat transfer between thesuperconducting film and substrate

T

T1

T2

Layer 1

Layer 2

Superconducting film

Substrate

[ ] [ ]

+

=

2

1

2

1

2

1

.

.

U

U

B

.

.

T

T

A

.

.

T

T

Tm = 77 K

Tm-1

m-ayer m-

Layer m

Surface in contact with liquid nitrogen

DUCXY

BUAXX

+=

+=

[ ] [ ]

+

=

m

2

1

m

2

1

m

2

1

mm

.

m

U.

.

U

U

D

T.

.

T

T

C

T.

.

T

T

UT

T

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Heat transfer between thesuperconducting film and substrate1

22

22

222

222

22

0

00

0

k

B,

-

0k2k-0000

0002k-k00000k2k-k0

0000k2k-k

00000kk-

A

=

=M

L

L

MMMOMMMM

L

L

L

L

2

22

2

22

1

222

dCk,

VC

1kwhere

0

0

0

0

0

0

0

D,

1000000

0100000

0010000

0001000

0000100

0000010

0000001

C

00000000

==

=

=

M

L

L

L

MMMOMMMM

L

L

L

L

L

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Heat transfer between thesuperconducting film and substrate

MgO STO YSZ

Thermal conductivity (W/m.K) 40.6 20 1.4

Specific heat capacity (J/m3.K) 3 106 1.216 106 2.5 106

Thermal

conductivity for

single crystal

sapphire

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177

227

277

erature(K)

Sapphire YSZ

77

127

0 0,2 0,4 0,6 0,8 1

T

emp

Distance (mm)

Temperature along the axis of

the substrateTscwhen usingdifferent substrates

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Temperature distribution for

Sapphire substrate layers

Temperature distribution for

YSZ substrate layers

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200

250

300

(V)

10A/mm^2

100A/mm^2

0

50

100

150

YSZ STO MgO Sapphire

Voltage

Substrate material

Maximum allowable input voltage with different substrate materials

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Effect of Substrate on the Weak Parts Problem

STO substrate MgO substrate

Neither STO nor MgO substrates are effective in solvingthe weak parts problem.

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Sapphire, Jc = 100A/mm2, lsc

= 10cm, and peak Vin = 80V

Sapphire, Jc = 100A/mm2, lsc =

60cm, and peak Vin = 400V

Sapphire substrate appears to solve small disturbances in

the temperatures of the different sections.


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Conclusion1. Liquid nitrogen has a negligible effect on Tsc during

the limitation time.

2. The thermal conductivity of the substrate plays amajor role in absorbing heat from the

superconducting film during and after the fault

, sc

voltage per unit length. This effect increases whenincreasingJc. Absorption of more heat decreases

the recovery time of the film.

3. YSZ, STO and MgO substrates have no effect on

solving any weak parts problem. However, sapphire

substrates can solve a mild weak parts problem but

fail in solving a severe weak parts problem.

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Simulation of the Shielded-

Inductive SCFCL


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Laboratory Set-up and

Ex erimental Procedures

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Introduction

Magnetic fields applied to the superconductingsample can be generated from a boost coil

connected in series or in parallel with the

superconducting sample. This coil can have either an

.

of both types of coil are covered. Irons higher permeability is expected to result in

improved figures of weight, resistance and

inductance. In order to ensure a uniform magnetic

field on the superconducting sample, it is envisagedthat the superconducting sample is located in an air

gap in the iron circuit.

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95

55

55

5

10

55

15

35

Configuration of the iron

core used for the iron-

cored coil (dimensions in

mm)

2

8

5

55

10

55

10

10

5

58

101

0

1

(a) (b) (c)

Configuration of the pieces

of material used for

insulating coil from the

iron core and keeping the

veroboard in uprightposition (dimensions in

mm)

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1010

3

Current probes

Voltage probes

1234

51

51

3

Superconductor sample

Schematic diagram of the DC 4-

terminal method

Superconducting sample (dimensions in mm)

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Circuits used for measuring I-Vcharacteristics of thesuperconducting sample

DC input

voltage

Pulsed

voltage

tnt

Current Probe

Am lifier

Line resistance

Gate

DriveInstrumentation

Amplifier

Digital

Storage

Oscilloscope

Superconducting

Sample

CurrentMeas

ureme

Voltage Measurement

IRF540

MOSFET


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Measuring the I-VCharacteristics of theSuperconducting Sample

8,0E-04

1,0E-03

1,2E-03

(V/cm)

0 mT

11 mT

22 mT

34 mT

57.75 mT

0,0E+00

2,0E-04

4,0E-04

6,0E-04

0 4 8 12 16 20

Electricfield,

E

Current density, J (A/mm^2)

Documents

Resistive SCFCL