High current splices
Summary of this talk• Quality assurance for the present interconnect work:
– Qualification work, modifications of machines– Control of parameters– Interconnect follow up (Christian Scheuerlein)
• Quality assurance for the series production– Quality plan– Measurement of electrical resistance during production– Mechanical QA testing during production
• Mechanical efforts on the 13 KA junctions– Nominal cases– Reduced overlap
• Summary of and electrical test on 13 KA joints to build high resistance splices
• Possible clamping
In other talks• Data mining: Nuria Catalan Lasheras• Calorimetric and voltage measurements: Nuria
Catalan Lasheras
QUALITY ASSURANCE FOR THE SERIES PRODUCTION
Quality control approach
The Quality Assurance (QA) strategy is based on four concepts:• Prior qualification of the processes, the equipment and the
operators on samples;• On-line monitoring and recording of critical parameters of all
junctions;• Strict application of the qualified procedures and full
traceability;• Production samples that can be tested off-line using
destructive methods.• From January 2007 till June 2007 72 persons were affected
to QC tasks. 110 were performing the assembly work
Controlling the quality I: the brazing • Before interconnecting:
– Interconnection qualification performed by ICIT (CERN) team– Intervention of the CERN team for repair if necessary– IEG inspection
• During the bus bar soldering– Control of the pressure and temperature performed by the machine: if they do not fit inside
the acceptable window the machine stops and/or indicate the a defective joint on the screen at the end of the cycle
• The pressure is measured via the hydraulic circuit• The temperature via a thermo-couple embedded in the joint
• After the soldering– Visual control by the operator according to CERN agreed procedure
• Geometrical defects: misalignment and lack of continuity between the pieces• Presence of soldering material in the junction between pieces
– The operator fills in the traveler– The recorded data are transferred to the company office and then in the CERN quality system
(problem of quality of data)– The quality controller of the team checks the work and the traveler. If he detects a problem
• Open a NCR• In case of doubt contact the CERN reference person for verification
Controlling the quality II: after the soldering
• Cleaning of the bus bar• Insulation of MB• US welding of the spool bus bars• Completion of the insulation with control
performed by the operator.• Electrical tests on half cells• Checking on the insulation before the welding of
the M lines: re-performed by the welder team leader
Controlling the quality III: the CERN role I
• Verification of application of the procedures:– Audits performed by CERN technician sampling the teams
• Tests on the assembly: electrical tests– PAQ tests (54): on pieces of the machine of 54m (half cell), 3
interconnects: 500 V, 30 sec, more in case of doubt (humidity …)– Connection of the half cells to form 5 sub-sectors: DS R, 11R-25R
25R-25L 25L-11L DSL, welding of the M lines sleeves in the PAQ tested interconnections
– MPAQ tests(5): 500 V 120 sec. more in case of doubt– Closing of the interconnects and leak tests– TP4-A 600 V 6 bar– TP4-E 1.9 KV 1 bar
Controlling the quality III: the CERN role II
– Tests of the machines: we used 8 machines. Every week one machine was selected to produce 2 samples for
• Electrical resistivity tests: 70 tests were performed• Mechanical tests: 56 tests were performed
– Each machine before being put in in service was qualified on samples to be mechanically and electrical tested
– US check of the joint quality: 230 (about 1380 joints) interconnects were sampled mainly in sector 6-7 and 1-2. 1 joint was found to be doubtful and re-soldered.
Data on qbqi.24 r3
• Dates– Brazing performed the 07/12/2006 Thursday. Team
Cescutti-Yanez– Checked by the IEG QC the 11/12/2006 Monday. L. Bouilly– Recorded by the team leader on the 11/12/2006. M.
Souayah– Isolation main bus bar. Ovivier Stefanidi 11/12/2006
• Team performing the work– Cescutti: leader contract started 23/01/2006 end
08/02/2007– Yanez: help contract started 31/08/2005 end 15/05/2007
AuditsAudits were the most difficult tool to put in place:• In order to get the confidence of the workers• In order to pass effectively the message to the
company on the points to be improvedThey started in October 2006, in January they
started to become very effective because of the relationship of technical trust that the workers built with the auditors that became their technical references
AuditsDate Machine Sector Result
30/10/06 BR4 3/4 Mis-positioning of thermocouple during repair of soldering
20/11/06 BR3 8/1 Geometrical problems 2 cycles
5/11/06 BR7 5/6 Problem in degreasing
10/11/06 BR8 5/6 ok
22/5/07 BR2 1/2 Procedure not properly applied
23/05/07 BR3 1/2 Lack of tools
21/05/07 BR4 1/2 Absence of thermo-couple during application of tin complement
24/05/07 BR6 6/7 Very good
Date recorded i.e. QQBI.23R3
Unfortunately only 30% of the LHC production data are exploitable: the choice of flash memory card to store the data has proven not to be strong enough to stand the environment near the HF generator of the inductive system
RESISTANCE MEASUREMENTS OF THE JOINT DURING PRODUCTION
Acceptability range for resistance
1) According to document LHC-QBBID-ES-0001 the resistance at 4.2K shall be less then 0.6 nΩ
2) The following guidelines for the evaluation of the tunnel samples have been implemented:
From 0 nΩ to 0.11 nΩ: too low not acceptable
sample
From 0.12 nΩ to 0.2 nΩ: ok
From 0.21 nΩ to 0.55 nΩ: strict machine
follow up
From 0.55 nΩ to 0.6 nΩ: stop machine
Above 0.6 nΩ out of tolerance
stop machine
Attention: a geometrically well done joint with no flux and no extra soldering in addition to the one present on the SC cables after
stripping present a resistance of 0.3-0.35 nΩ
Joint resistance measurement on samples
Copper cover twisted: joint non conform it was decided to ahead to see the effect on the joint resistance
Machines used in sector 3-4
Overall tests performed
Aug-06 Sep-06 Oct-06 Nov-06 Dec-06 Jan-07 Feb-07 Mar-07 Apr-07 May-07 Jun-07 Jul-07 Aug-07 Sep-07 Oct-070
2
4
6
8
10
12
month
Nm
ber o
f tes
ted
sam
ples
Electrical tests on machine BR 2
Period of use in sector 3-4
Aug-06 Sep-06 Oct-06 Nov-06 Dec-06 Jan-07 Feb-07 Mar-07 Apr-07 May-07 Jun-07 Jul-07 Aug-07 Sep-07 Oct-070
0.5
1
1.5
2
2.5
month
Num
ber o
f tes
ted
sam
ples
Electrical tests on machine BR4
Period of use in sector 3-4
Aug-06 Sep-06 Oct-06 Nov-06 Dec-06 Jan-07 Feb-07 Mar-07 Apr-07 May-07 Jun-07 Jul-07 Aug-07 Sep-07 Oct-070
0.5
1
1.5
2
2.5
month
Num
ber o
f tes
ted
sam
ples
Electrical test on machine BR7Period of use in sector 3-4
Special testsDuring the interconnection in sector 3-4 a special tests was
performeda) 4 long dipole bus bar elements were prepared (80 cm
on each side)b) The 4 elements were interconnected by IEG operator
using production machine in the tunnel on the 28/11/06 (sector 3-4 !!!)
a) N. 1: with standard interconnectb) N. 2: forgetting the soldering material between the 2 cables
c) The 2 elements were measured in the Fresca facility:a) N.1 0.38 nΩb) N.2 0.28 nΩ
MECHANICAL QA TESTING DURING PRODUCTION
Mechanical test procedure and acceptance limits
• At room temperature– Fatigue life cycle: 5000 cycles from 20 N to 240 N– Tensile test: minimum force for joint breakage 900 N
• At 4.2 K– Fatigue life cycle: 5000 cycles from 40 N to 510 N– Tensile test: minimum force for joint breakage 1000 N
• Total number of tests performed: 34 R.T., 46 4.2 K
Production samples
The check was performed by the execution, by the same operators using that specific machine, of two production samples. After a visual inspection, the samples were tested electrically at the CERN cryolab and thereafter mechanically at the EIG (Ecole d’Ingénieurs de Genève).
Important: no one of the joints tested was broken during the tests. A test was stopped because
1) An upper test limit due to the test set up was reached ( typically 2 KN for the 4.2 K and 5 KN for the R.T. tests)2) A discontinuity on the loading curve was observed (see case I and case II) and that value was declared the limit of the joint
Test equipment EIG
Tensile test R.T.
0
1000
2000
3000
4000
5000
6000
1 2 3 4 5 6 7
Forc
e [N
]
soldering machine
Average F R.T. [N]
min F [R.T.]
max F[ [R.T.]
Tensile test 4.2 K
0
1000
2000
3000
4000
5000
6000
1 2 3 4 5 6 7
Forc
e [N
]
Soldering machine
Average 4.2 K [N]
min F [R.T.]
max F[ [R.T.]
Tests of main machines used in 3-4
• Machine BR4 tested conform on the – 20/09/06 R.T. fatigue 4.2K tensile (>5000 N)– 31/10/06 4.2 K fatigue and tensile test (>4800 N)– 23/01/07 R.T. fatigue and tensile test (>1900 N)– 06/02/07 4.2K fatigue and tensile test (>5000 N)
• Machine BR7 tested conform on the – 11/10/06 R.T. and 4.2 K. fatigue and tensile test (>1900 N
and >4000 N)– 23/01/07 R.T. fatigue and tensile test (>1900 N)– 06/02/07 4.2 K fatigue and tensile test (> 4000 N)
Ultrasound Checks on Busbars M1,M2,M3An ultrasound diagnostic system probing along a horizontal axis above the cables and that is able to detect this vertical gap has been implemented to reinforce the quality control process . Micro U-Sound probes are clamped into contact with both sides of the bus-bar junction. The system detects the absence of added brazing alloy between the copper cover and the U
Ultrasound Checks on Busbars M1,M2,M3
Ultrasound Diagnostic System
Main Bus-bar Junction
Clamp
Measurements are made at 4 equi-distant locations, along the length of the junction where the clamping system is positioned perpendicular to the bus-bar. The results of each measurement are automatically stored and a go no-go diagnosis of the junction quality at each location according to the pre-set limit is made. Measurements on all 6 bus-bars in an interconnect, 24 in total, were carried out. A soldered junction was rejected if 3 out of the 4 measurements are below the acceptance limit.
Ultrasound Checks on Busbars M1,M2,M3The thin green trace is from a junction that was prepared under carefully controlled laboratory conditions and looks flawless visually. The typical features of such a “good” trace are (1) very good transmission at a distance corresponding to the junction thickness and (2) a few smaller peaks later on due to multiple reflections from the various interfaces in the set-up. The pre-amplification of the ultrasound device was set such that a good trace covers roughly the full display scale. The thick blue trace was taken on a junction that was soldered without any additional tin/silver alloy at all. The small amount of residual soldering alloy on the cable strands sticks the junction box together forming a “dry joint” whose mechanical strength is low. Since no tin/silver alloy climbs up the sides of the junction, the transmission signal consists only of reflected waves that travelled around the lower U shaped copper piece. The signal is much smaller and it arrives later than for a good junction.
Ultrasound Checks on Busbars M1,M2,M3LHC
SECTORBus-Bars
TestedMeasurements
MadeMinor Defects
Non-Conformity
Re-soldered and Re-
measured1-2 926 3704 13 1 12-3 126 504 1 0 03-4 34 136 0 0 04-5 0 0 0 0 05-6 6 24 0 0 06-7 296 1184 10 0 07-8 0 0 0 0 08-1 0 0 0 0 0
Total 1388 5552 24 1 1
One junction (QQBI.20R1, in sector 1-2) with 3 measurements out of 4 below the acceptance limit has been found. According to LHC Quality Assurance Procedures this junction was declared non-conform (see NCR 836841 ) and was immediately re-soldered with more tin/silver alloy being added to the junction, and re-measured. The repeat measurement showed the re-soldered junction to be fully conforming. No junctions with 4 out of 4 measurements below the acceptance limit (corresponding to a case where additional tin/silver soldering alloy has been omitted) have been found.
DefinitionsMinor Defect: Up to 2/4 measurements below thresholdNon-Conformity: 3 or 4/4 measurements below threshold
MECHANICAL EFFORTS ON 13 KA JUNCTIONS
Mechanical forces on the splice
• Room temperature: compressive longitudinal force due the compression of the lyre for about 47 mm=450 N
• With current and with perfect current re-distribution :– Vertical direction (y). Total force on each joint is null but
the 2 cables are submitted to a force towards the joint plane
– Horizontal direction (x). The 2 joints are submitted to force rejecting the 2 bus bars
Compressive force on lyre at RT vs. displacements
Bus bar loading case
M3 spider lyra side
Bus bar support connection side
Forces and displacements at cold (bus bar fully restrained by the spiders)
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 11000 12000 130000
100
200
300
400
500
600
700
800
900
1000
1100
1200
0.000
0.010
0.020
0.030
0.040
0.050
0.060
0.070
0.080
0.090
0.100
0.110
0.120
X force
displacement
Current [A]
Forc
e [N
]
Disp
lace
men
rt X
[mm
[
Loading case I: nominalThe spider and the connection side support are tightly
closed around the bus bar providing full mechanical restrain. Distance between the 2 elements is nominal (450 mm). The 1.5 mm thick steel jacket prevents important spider deformations (< 0.01mm)
The bus bar behave like a beam fully restrained at the extremity charged by distributed load. A bending moment develops along the length creating a tensile stress on the outer edge and a compressive stress on the inner edge
Shear stress in the bus bar copper profile
-25
-20
-15
-10
-5
0
5
10
15
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
Shea
r str
ess
[MPa
]
Position [m]
Shear stress on the copper edge
Shear stress on the cable edge
Shear stress in the bus bar SC cable imposed displacement
-1.5
-1
-0.5
0
0.5
1
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
Shea
r str
ess
[MPa
]
Position [m]
Shear stress on the cable edge
Considering only the part of the cable in traction this corresponds to 320 N (140 N 8700 A). Neglecting the stress profile we get to 1250 N (550 N 8700 A)
0.31 MPa at 8700 A
Loading case II: loose spider• The spider could present a gap between the G11
inner part and the bus bar. The “radial” gap is between 0.5 mm and 0.7 mm
• The gap is filled with fiber glass or epoxy during the spider assembly at the CM assemblers. If it is not filled this would provide a more severe mechanical loading condition for the interconnect. The us bar would act as beam on simple supports. The sagitta at 13KA would be of 1.1 mm just enough to fill the gap
Limit case
• We consider that the spider is loose and therefore that the bus bar is only supported
• We neglect the contribution of the bus bar externally to the supports and the balancing effect of the magnetic forces acting on those sections
Shear stress in the bus bar SC cable imposed displacement
loose spider
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.50
0.5
1
1.5
2
2.5
shear stress on the joint
position [m]
Sigm
a[ M
Pa]
Considering only the part of the cable in traction this corresponds to 1500 N (660 N 8700 A). Neglecting the stress profile we get to 3800 N (1670 N 8700 A)
1.3 MPa at 8700 A
Spiders displacements
Cases of spiders’ displacement 13 KA
MB-MB MB-SSS SSS-MB
Max displacement lyra side
50 mm 50 mm 50 mm
Max displacement connection side
30 mm 30 mm 100 mm ?
Max σ bus bar fully restrained
1 MPa 1 MPa 1.3 MPa
Eq traction force restrained
480 N-1700 N 480 N-1900 N 900 N-2250 N
Max σ bus bar on supports
3 MPa 3 MPa 4 MPa
Eq traction force supported
2250 N-5300 N 2250 N-5300 N 3200 N-6800 N
Electromagnetic forces
Cable_1
Cable_2
Cable_3
Cable_4
Magnetic forces distribution due to current profile
-14
-12
-10
-8
-6
-4
-2
0
2
4
0 2000 4000 6000 8000 10000 12000 14000
Fmag
(N)
I (A) on lower cable
Fx
Fy
Bus bar rotation around its center line
Stresses along the bus bar
-30
-25
-20
-15
-10
-5
0
5
10
15
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
Shea
r str
ess
[MPa
]
Position [m]
Shear stress on the copper edge
Shear stress on the cable edge
Shear stress in the bus bar copper[ansys]
-2
-1.5
-1
-0.5
0
0.5
1
0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
Shea
r str
ess
[MPa
]
Position [m]
Shear stress on the cable edge
Shear stress in the joint only SC cable[ansys]
Considering only the part of the cable in traction this corresponds to 350 N. Neglecting the stress profile we get to 1400 N
Re-evaluation of the junction forces in function of the junction length
Transverse current = 0.1*J = 120mm splice
-40
-30
-20
-10
0
10
20
30
40
50
60
1 2 3 4 5 6 7 8 9 10
splice volume fraction
Fy
Lower cableUpper cableTotal Fy on spliceTotal Fy on joint
Transverse current = 0.2*J = 60mm splice
-40
-30
-20
-10
0
10
20
30
40
50
60
1 2 3 4 5 6 7 8 9 10
splice volume fraction
Fy
Lower cableUpper cableTotal Fy on spliceTotal Fy on joint
Soldered part
Transverse current = 0.25*J = 48mm splice
-40
-30
-20
-10
0
10
20
30
40
50
60
1 2 3 4 5 6 7 8 9 10
splice volume fraction
Fy
Lower cableUpper cableTotal Fy on spliceTotal Fy on joint
Soldered part
Transverse current = 0.5*J = 24mm splice
-40
-30
-20
-10
0
10
20
30
40
1 2 3 4 5 6 7 8 9 10
splice volume fraction
Fy
Lower cableUpper cableTotal Fy on spliceTotal Fy on joint
Soldered part
-200
-150
-100
-50
0
50
100
150
200
250
300
0 20 40 60 80 100 120 140
Splice length
Fy
Total force on splice
Total force on joint
Summary of and electrical test on 13 KA joints to build high resistance splices
C .Scheuerlein, Pierre A. Thonet, C. Urpin,Cryolab, Superconducting laboratory
Joint resistance measurement on samples during series production
Copper cover twisted: joint non conform it was decided to ahead to see the effect on the joint resistance
Results of effect of mechanical load on a joint resistance. Force necessary to fully extend a lyra 500-1000 N
Joint type R before mechanical test R after mechanical test 500 N
Quadrupole 0.1 nΩ 0.1 nΩ
Dipole 0.09 nΩ 0.09 nΩ
Joint type R before mechanical test R after mechanical test 1000 N
Quadrupole 0.13 nΩ 0.13 nΩ
Dipole 0.12 nΩ 0.10 nΩ
Joint type R before mechanical test R after mechanical test 5000 N
Quadrupole 0.1 5nΩ 0.14 nΩ
Dipole 0.11 nΩ 0.11 nΩ
Effect of repair proceduresRe-heating of the joint to 270 C without applied force to
simulate the operation required to fill longitudinal gaps: 0.18 nΩ
Effect of repeated cycles of brazing and de-brazing
• 2nd cycle 0.2 nΩ• 3rd cycle 0.18 nΩ• 5th cycle 0.17 nΩ
Geometric non conformity of the assembly
• Copper cover inversed with Sn-Ag (heated): 0.16 nΩ• Copper cover inversed without Sn-Ag (heated): 0.17 nΩ
Misplacement of copper cover
Misplacement of 2 strands
• 2 strands misplaced 0.21 nΩ
Samples mechanically assembled without heating
Three samples of joint only mechanically assembled were produced (no heating of the joint)
– With all the tin layers, U of copper mechanically closed on the sides and mecha
SnAg layers Pressure kept using Heating R
no vise no 5 µΩ
yes Tig spots no 9 nΩ
no Tig spots no 0.5 nΩ
Absence of SnAg and effect of pre-tinningSoldering material
Kester Pre tinning applied using
Heating R
No (1st test) no oven yes 0.25 nΩ
no no oven yes 0.2 nΩ
no no oven yes 0.22 nΩ
no no Heating plate yes 9.3 nΩ
no no Heating plate yes 9.8 nΩ
Poorly pre-tinned cable hand madeA splice was made of deliberately poorly pre-tinned cable ends, without
addition of solder. It can be seen that the insufficient pre-tinning and the presence of oxidised Cu intermetallics prevents that an intimate contact can be formed between the two cables, which can be easily separated from each other when the Cu plate is removed.
After the standard heating cycle under a pressure of about 12 MPa the contact resistance is 9 nΩ. Mechanical resistance 3.3 KN to be repeated at 4.2 K
Resistance of joint over heated
560 °C
240 °C
500 °C in the splice. Al block about 600 °C Measured resistance 1.9 nΩ
Over-heating till 420 C . No visual effect on bus bar R=0.19nΩWhich max temperature could be achieved ?
Mechanical resistance of joint marginally heated over the SnAg melting temperature
Rupture force 13KN: normal
CLAMPING
Solution I
1) Fully insulating2) Re-using existing insulation scheme3) Applying vertical force4) Blocking laterally the bus bars
Problem of solution I
• Accepting the mechanical tolerances due the copper pieces deformation keeping enough material
Solution II
1) Using also steel pieces and screws2) Re-using existing insulation scheme3) Applying vertical force4) Blocking laterally the bus bars if possible
Using of a rivet
We are not found of because the irreversible damage to the SC cable would make almost impossible the de interconnection and reconnection of a magnet
Personal concern about clamping efficiency
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