insulation co-ordination and high voltage testing of fusion magnets

7/31/2019 Insulation Co-Ordination and High Voltage Testing of Fusion Magnets

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S. Fink ITP 07.04.2009

KIT die Kooperation von

Forschungszentrum Karlsruhe GmbH

Stefan Fink:

MATEFU Insulation co-ordination and highvoltage testing of fusion magnets

Le Chateau CEA Cadarache, FranceApril 7th, 2009

Insulation co-ordination Some principle considerations of HV testing Testing of ITER TF Model Coil ITER TF


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S. Fink ITP 07.04.2009



Insulation co-ordination

Insulation co-ordination is the selection of test voltage(s) in relationto the operating voltages and overvoltages which can appear on thesystem.

System analysis

Representative voltages and overvoltages

Test voltages

Example in conventional HV

engineering: waveform for a standardlightning impulseMultiplying with factors

Voltage value, waveform, test time

Voltage value, waveform


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Representative voltages for TF coil discharge

Difficult to make a single HV test which is relevant for all voltages (and overvoltages)

which may appear on the coil

=> A set of tests with different waveform is used

Most representative

Stresses all types of

insulation

Non destructive

insulation diagnostic

possible (e. g. partialdischarge (PD))

Simple, cheap

Low destructive

Representative for fast

excitations (fastswitching, faults)

Representative for

increase if arc chutebreakers are used

Representative for fall

ImpulseAlternating voltage

("AC")

Direct voltage

("DC")

1 2

Winding

Case

1 2

Winding

Case

1 2

Winding

Case


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devices

Large devices may have internalovervoltages if they are subjectedto fast excitations=> calculation of transient

behaviour:Non linear voltage distribution?Oscillations?

Non destructive test methods=> Partial discharge measurement

20 kV transformer of a 50 kA power supply


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tight apparatus

A Paschen tight device can beoperated independently of thesurrounding dielectric properties (e.g. during vacuum breakdown).

The ITER TFMC was designed withsolid insulation covering completely

the HV areas. The insulation iscovered with conductive paint. Thispaint is grounded.

Verification if a coil is Paschentight is performed by HV DC testingwith the transition of the Paschencurve of the surrounding air in the

cryostat at room temperature. Paschen tight apparatus

Current Lead

Insulated test

sample coveredwith conductivepaint

Undefinedgas or vacuum


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ITER Toroidal Field Model Coil (TFMC)

Coil parameters:

Rated current 80 kARated voltage +5 kV / -5 kVDouble pancakes 5Turns per pancake 10 (or 9

for outermost)

Design of ITER TFMC

Coil Case Winding Pack

Cross Section

3 different insulation types: Conductor insulation Radial plate insulation Ground insulation

FEM d k d l f ITER TFMC


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FEM and network model for ITER TFMC

2D-FEM model of ITER TFMC as

basis for calculation of the lumpedelements of network model Network model of ITER TFMC

UniversityKarlsruheUniversity Karlsruhe

R lt f t i t l l ti f TFMC


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Results of transient calculation for TFMC

First resonance frequency appears at 290 kHz for the relevant cases 2 and 3.(This was later conformed by low voltage / high frequency measurement on ITER TFMC.)

0,0

0,5

1,0

1,5

2,0

2,5

3,0

3,5

0 100 200 300 400 500

Frequency [kHz]

|G(f)|

Case 1

Case 2

Case 3

Transfer function at node 1 of the ITER TFMC

network model with symmetric voltageexcitation 5 kV

The selected configuration with connection of the radial plate by 1.2 M resistors ana symmetrical grounding gives no relevant overvoltages for rise times above 2 s

=> No high overvoltages expected for all prepared HV tests

T i l HV t t f ITER TFMC


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Typical HV tests for ITER TFMC

DC test on ground insulation Impulse test DC test on ground insulation

DC and AC test on ground, radial plateand conductor insulation without roomtemperature instrumentation cables

DC test on ground insulation

DC test voltage value for ground insulation was 10 kV (test voltages forother insulation types and waveforms had been lower)

Tests were performed at room and cryogenic temperature AC tests included partial discharge measurement

Grounde

case

Ground

insulation

Radial plateinsulation

Conductorinsulation

Conduct

Radial plat


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temperature

All tests under ambient conditions werepassed successfully

During Paschen test it was found thatTFMC is not Paschen tight

2 potential fault locations were found,Tedlar tapes were forgotten to remove

during manufacturing at one location

Fault location at helium inlet tubes


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ITER TFMC at cryogenic temperature

Breakdown strength for AC and esp.impulse testing under cryogenicconditions does not fulfil thespecification

High current discharge withI = 80 kA and U < 1 kV was possible

High voltage discharge was reducedfrom +5 kV / -5 kV to 0 / 4.4 kV

=> ITER TFMC does not fulfil the HVspecification Breakdown during an impulse test

with 5 kV at the plus terminal

0

12

3

45

0 10 20 30

SC1116.QDA

Uplus terminal

UkV

t

s

ITER TF


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ITER TF

ITER TF coils

Coil design parameters:

Rated current 68 kAVoltage @ fast discharge 3.5 kV

Number of coils 18Double pancakes / coil 7Number of turns / pancake 11 (outer

DP: 3, 9)

Cross section of an ITER TF coi


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Resonance frequencies of ITER TF


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Resonance frequencies of ITER TF

The resonance frequency of a single ITER TF coil is calculated to be 50 kHz

0

5

10

15

20

25

30

35

0 50000 100000 150000 200000

Uterminal2

UHeIn7

UHeIn6

UHeIn5

UHeIn4

UHeIn3

UHeIn2

UHeIn1

UR134:2 - RP7

UR131:2 - RP7

U = f(f) on the 50 kHz model for anexcitation with 1 V. First resonanceoccurs at 50 kHz => natural frequency iscalculated to be 50 kHz

ITER TF discharge circuit


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ITER TF discharge circuit

18 TF coils

9 fast discharge

units (FDUs)

Soft grounding

TF discharge circuit (simplified)

FDUFDU FDU

FDU FDUFDU

TF Coil

Grounding resistor

Fast discharge unit

=> A model is required tocalculate terminalvoltages

Network model of 18 ITER TF coils


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Network model of 18 ITER TF coils

Output: maximum terminal to ground

voltage maximum terminal to terminal

voltage

ITER TF system with 18 simplifiedsuperconducting coils (established

by University of Karlsruhe, IEH)

VV V-V+

R66

0

C51

R68

500

R69

0

C52

0

R71

C53

R73

0

C54

L19 L20 L21 L22 L23 L24

I1

+

-

+

-

S3

S

V3

0

L25 L26 L27 L28 L29 L30

C7

C1C2

C3 C 4 C5C6

C8

C9 C10 C11 C12

C13C14 C15

C16 C17C18

C19C20

C21 C22C23

0

C24

C25 C26C27

0

0

0

0000

0

00 00

0

0

0

0 00 0

0

0

0

0

0 00

FDU1

TF_FDU

ei n a us

L31 L32 L33 L34 L35 L36

L37 L39 L40 L41

L42L43

0

L44

C31

R27

0

R25

C30

R20

C28

R22

0

C29

0

L45

C32

R29

0

C33

0

R31

R32

C34

0

L1

0.349H

L2

0.349H

R1500

R2

500

R34

0

C35

L4

0.349H

FDU2

TF_FDU

e in a us

R36

L3

0.349H

R4

500

C36

0

R3

500

R6

500R7

500

L6

0.349H

L8

0.349H

R38

R8

500

FDU3

TF_FDU

e in a us

0

C37

L5

0.349H

FDU4

TF_FDU

e in a us

L7

0.349H

R5

500

R10

500

L14

0.349H

R11

500

R40

R13500

L10

0.349H

L16

0.349H

L13

0.349H

R14

500

FDU7

TF_FDU

ei n a us

L12

0.349H

C38

0

R12

500

FDU5

TF_FDU

e in a us

R16

500

L9

0.349H

L11

0.349H

FDU6

TF_FDU

e in a us

R15500

L15

0.349H

FDU8

TF_FDU

e in a us

R9

500

R42

C39

0

R18

500

FDU9

TF_FDU

e in a us

L17

R17500

0

L18

R44

C40

0 0

R46

C41

R48

C42

0

R50

0

C43

R52

C44

0

R54

C45

0

R56

C46

0

R58

C47

0

R60

C48

0

R62

0

C49

R64

C50

0


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Calculated voltages in time domain


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Calculated voltages in time domain

The calculated terminalvoltages are in goodagreement with some ITERDDDs.

But non linear internalvoltage distribution wasfound already during fastdischarge without fault whichwas not in agreement withthe simple calculations of theITER DDDs (where only

linear internal voltagedistribution is assumed).

For an ideal fast discharge all coils have thesame maximum voltage of 3.5 kV to groundand between both terminals of each coil.

=> HV tests are required to confirm proposed test

voltages are compatible with ITER design

-2000

-1000

0

1000

2000

3000

4000

5.000 5.020 5.040 5.060 5.080 5.100

FD without fault - L8

UL8 terminal1

UL8 terminal2

Long term testing on ITER TFMC


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Long term testing on ITER TFMC

Insulation: conductor and radial plate insulation

(ground insulation has fault) Maximum voltage test value derived fromcalculation of transient behaviour:11 kV peak (factor compared to TFMCacceptance tests: 4 for DC and 8 for AC)

Voltage waveform: DC and AC Duration of 3 voltage steps each: 10 h

No voltage breakdown appeared duringDC test (UDC, max = 11 kV)

Breakdown appeared after 9 h 39 min of7.78 kVrms on ground insulation duringconductor insulation test on known fault

location (increase of PD activity 15 minbefore breakdown)

ITER TFMC outside the cryostat

=> Proposed test values for conductor

and radial plate insulation would be OK

Burn out of fault location on ITER TFMC


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Burn out of fault location on ITER TFMC

The burn out confirmsthe assumption of thefault location

Flashes around the helium tubesduring burn out

Conclusion for ITER


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Conclusion for ITER

Calculation of terminal voltages and assuming only linear voltage

distribution is not enough for prediction of internal voltages

A Paschen Test is indispensable to prove high voltage strength during

vacuum breakdown

A cold test is recommended to verify reliable HV operation at cryogenictemperature

Conductor and radial plate insulation can withstand the proposed testvoltages derived from calculation of transient behaviour of ITER TF inspecial fault case for 10 h without breakdown.=> 1 working day (8 h) Paschen Test with permanently applied highvoltage would be possible

End


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End

3D FEM model for ITER TFMC


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3D FEM model for ITER TFMC

3D-FEM model of ITER TFMC fordirect voltage calculation

(University of Karlsruhe)

Terminal voltages in time domain (TF-7)


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e a o tages t e do a ( )

Maximum voltage to ground in faultcase 2 is 16.35 kV (t = 5.0877 s,tr = 3.5 ms, terminal L8:2)

-5000

0

5000

10000

15000

20000

5.000 5.020 5.040 5.060 5.080 5.100

failure of FDU 2 and 3 + earth fault 3-1

Uterminal 2:1

Uterminal 2:2

Uterminal 8:1

Uterminal 8:2

-2000

-1000

0

1000

2000

3000

4000

5.000 5.020 5.040 5.060 5.080 5.100

FD without fault - L8

UL8 terminal1

UL8 terminal2

For an ideal fast discharge all coilshave the same maximum voltageof 3.47 kV to ground and betweenboth terminals of each coil.Rise time: tr = 1.6 ms.

Frequency measurements on ITER TFMC


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q y

Calculated (network) andmeasured resonance

frequency show goodagreement for the relevantcases

Damping directly in resonancecase and above was calculatedwith poor accuracy sometimestoo low and sometimes too

high

Comparison of the transfer functions on

outermost inner pancake joints for radialplates connected over resistors and

symmetric excitation.

0

0,5

1

1,5

2

2,5

0 100 200 300 400 500

FRS.QDA

|G|FRS

calculated Case 2 5 kV

|G(f)|

f

kHz

insulation co-ordination and high voltage testing of fusion magnets

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