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7/31/2019 Insulation Co-Ordination and High Voltage Testing of Fusion Magnets
1/27
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
7/31/2019 Insulation Co-Ordination and High Voltage Testing of Fusion Magnets
2/27
S. Fink ITP 07.04.2009
KIT die Kooperation von
Forschungszentrum Karlsruhe GmbH
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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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
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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S. Fink ITP 07.04.2009
KIT die Kooperation von
Forschungszentrum Karlsruhe GmbH
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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S. Fink ITP 07.04.2009
KIT die Kooperation von
Forschungszentrum Karlsruhe GmbH
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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7/31/2019 Insulation Co-Ordination and High Voltage Testing of Fusion Magnets
8/27S. Fink ITP 07.04.2009
KIT die Kooperation von
Forschungszentrum Karlsruhe GmbH
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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9/27S. Fink ITP 07.04.2009
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Forschungszentrum Karlsruhe GmbH
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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10/270 S. Fink ITP 07.04.2009
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Forschungszentrum Karlsruhe GmbH
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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11/271 S. Fink ITP 07.04.2009
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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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Forschungszentrum Karlsruhe GmbH
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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13/273 S. Fink ITP 07.04.2009
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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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14/274 S. Fink ITP 07.04.2009
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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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16/276 S. Fink ITP 07.04.2009
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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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7 S. Fink ITP 07.04.2009
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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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8 S. Fink ITP 07.04.2009
KIT die Kooperation von
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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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0 S. Fink ITP 07.04.2009
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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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1 S. Fink ITP 07.04.2009
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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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2 S. Fink ITP 07.04.2009
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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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3 S. Fink ITP 07.04.2009
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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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5 S. Fink ITP 07.04.2009
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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