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Quench
Quench

Quench - PowerPoint Presentation

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Protection of the Hi Lumi CCT Corrector Magnets 1 M Mentink J van Nugteren G Kirby March 8 th 2017 Motivation Quench protection of Hi Lumi CCT corrector coils 2 versions 05 meter ID: 541212 Download Presentation

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Presentation on theme: "Quench"— Presentation transcript

Slide1

Quench Protection of the Hi-Lumi CCT Corrector Magnets

1

M. Mentink, J. van

Nugteren

, G. Kirby

March 8

th

2017Slide2

Motivation

Quench protection of Hi-

Lumi CCT corrector coils2 versions: 0.5 meter model magnet and 2.2 meter prototype magnetQuench behavior is intrinsically 3D, both longitudinal quench propagation and transverse heat exchange play a roleQuench behavior determines appropriate level of extraction, which affects insulation requirements  3D modeling needed to understand quench behavior

2Slide3

Previous work by

Juho

RustiPrevious evaluation of quench behavior by Juho Rysti [1]3d thermal model in Comsol (FEM solver)Heat balance equation solved for a model with a few turns, and resulting quench velocities are applied to entire magnet geometryResults:Short magnet is intrinsically safe: No extraction  Thotspot = 190 KLong magnet requires extraction: R

dump

= 1.4

Ω

, tswitchdelay = 12 ms  Thotspot = 190 K

3

1. Kirby et al., IEEE

Trans. On Appl.

Supercond

. 27, p.

4002805

(2017)Slide4

Overview

New 3d model: modeling assumptions

Thermal heat transferMaterial propertiesQuench BackModeling resultsComparison with Juho’s resultsGeneral overview of temperature and voltage resultsQuench Protection parameter variationsSummary

4Slide5

3d model assumptions: Thermal transfer

Matlab

model with heat transfer in all three directionsTransverse heat transfer within turn:1 node per domain, insulation and strands are separate domains with separate temperature-dependent properties105 transverse nodes = 20 strand nodes + 4 x 20 strand insulation nodes + 3 former element nodes + 2 former insulation nodesEffective thermal thickness of E-glass strand insulation: 180 µm, calculated with ComsolLongitudinal heat transfer (from perspective of strand): 50 elements per turn, longitudinal quench propagation velocity follows directly from heat balance equationTurn-to-turn heat transfer (includes strand insulation to strand insulation)Helium cooling: T < 32 K: 1 W/cm2, T > 32 K: film boiling regimeNumerical aspectsBrute force solving (no adaptive mesh)Typical run-time: 40 mins for 320k nodes, scales linearlyInvestigation of longitudinal node density vs. Thotspot indicates convergence

5

4mm

15 mm

0.2 mm

polyimide

6.6 mm

0.2 mm

polyimide

6.6 mm

LHe

, 1.9 K

LHe

, 1.9 K

Transverse heat transfer Slide6

Material properties

Material properties

Formers: Aluminum-6000 series, RRR = 2.9Former insulation: Polyimide (0.2 mm thick)Strand insulation: Fiberglass (E-glass) + epoxy resin (Cv = Cv,G10, k = kG10 x 1.6 [2]) NbTi strand type: MB outer layer strand, D = 0.825 mm, Cu : nonCu = 1.95, in-field RRR = 62Magnetic field per group of strands varies between 3 and 1.8 T per turn when current is at 435 AIc(3T, 1.9 K) = 1130 A Operating current of 435 A is at 38% of short sample, and at 55% of load lineCurrent sharing temperature:

T

cs

= 5.7 K,

3.8 K marginBoth temperature and field dependence of NbTi are considered in quench protection calculation

6

2.

Imbasciati

et al., FNL TD-03-019, FNL / Univ. of Milan / INFN

(2014)

3. Data provided by A. Verweij

, also see IEEE Trans. on Appl. Supercond. 16,p

.

1192 (2006)

NbTi

MB

outer layer strandSlide7

Quench back

Electrical and inductive calculations (simultaneously with thermal calculations)

Approach: Numerical solution (where M and R are matrices and I is a vector):Quench back: Assumes homogeneous current flow through former cylinders, inductances based on assumed saddle coil current flow  Likely somewhat pessimistic with regards to quench backInductances are corrected for presence of iron, but linear behavior assumed (i.e. inductances are independent of current)

7

 

Quench back current flowSlide8

Comparison with

Juho’s

resultsComparison of resultsWith quench back suppressed, new model is slightly more pessimistic (190-200 K) vs. 220 KDifferent underlying assumptions (bronze former vs. aluminum former, 5 strands per slot vs 10 strands per slot, cable vs. individual strands, etc.) may explain this 20-30 K differenceQuench back makes a big difference: 220 K without QB, 80 K with QB!

8

R

dump

= 1.4

Ω

,

t

delay = 12 msJ. Rysti’s resultsResults of the new modelSlide9

Typical temperature and voltage distributions

9

Typical temperature and voltage

distributions along the strands

Quench originates in middle of strand bundle on inner former, in middle of magnet

Calculation result: Inhomogeneous quench back

 First strands on outer former quench (due to lack of direct helium cooling), followed by strands on inner former

Strands on inner former

Strands on outer former

Position along length of strand

x

[m]

Temperature [K]

Formers

Thick outer cylinder

0

100

8 12 16 20 24 28

50

Position along length of strand

x

[m]

Voltages [V]

Peak imbalance = Peak voltage between neighboring strands ≈150 V

-350

0

0 220 440

2.2 meter long magnet,

R

dump

= 1.0

Ω

,

t

switch,delay

= 25

msSlide10

Overview of results

10

Overview of results for “standard” quench protection setup

standard”

quench protection setup:

1.0

Ω dump resistor 25 ms

delay between quench origination and opening of switch

With aluminum formers, quench back, helium cooling

Results:

Peak Thotspot = 140 KPeak voltage to ground: 435 V (= 1.0 Ω x 435 A)Peak voltage between neighboring strands: 150 VOpening of relay after 25 msStrands on outer former normal due to quench back

Normal zone formation on outer former

Normal zone formation on inner former

2.2 meter long magnet,

R

dump

= 1.0

Ω

,

t

switch,delay

= 25

ms

Opening of relay after 25

msSlide11

Quench Protection parameter variations

11

Quench protection parameter variations

Higher dump resistor, faster switch opening

 lower

T

hotspotQuench back  much lower Thotspot

Operating current increases 

T

hotspot

increases

Iop = 435 ARdump = 1.0 Ω, tswitchdelay = 25 msSlide12

Summary

12

New three-dimensional model

Three dimensions: Longitudinal (from strand perspective) and both transverse directions

Considers thermal exchange between strands, formers, neighboring turns, neighboring formers, etc.

Quench back included (in somewhat rudimentary manner, likely somewhat pessimistic)

ObservationsComparison to Rysti’s Comsol model: Generally consistent results if quench back is suppressed

Quench back strongly reduces the peak hotspot temperature (typical reduction: more than 100

K

)

Peak voltage to ground dominated by dump resistor (

Vground,max = Iop x Rdump)As rule of thumb, peak voltage between neighboring strands typically equal to 30 to 40% of peak voltage to groundResults & variationsRdump = 1.0 Ω, tswitchdelay = 25 ms  Thotspot = 140 K with quench back, 270 K without quench backHotspot temperature decreases with increasing Rdump

and decreasing tswitchdelay

.

For instance:

R

dump

= 1.4

Ω

,

t

switchdelay

=

12

ms

T

hotspot

= 80 K (with quench back)

Hotspot temperature increases with operating current For instance: Rdump = 1.0

Ω, tswitch,delay = 25 ms,

Iop = 735 A  Thotspot

= 280 K (with quench back)