MPE actions from last review and circuits screening

Second LHC Splice Review, November 28-30, 2011

Rüdiger Schmidt, TE-MPE reporting for …..

R.Mompo, G.d’Angelo, M.Bednarek, N.Catalan-Lasheras

A.Verweij, E.Ravaioli, S.Rowan, D.Molnar

K.Dahlerup-Petersen, M.Zerlauth

S.Pemberton, K.Pereira

A.Ballarino, H.Thiesen, A.Siemko

+ others

1

Overview Magnets Electrical Circuits Screening

1. Information on magnet and powering system

2. Electrical and thermodynamic modelling of the magnets / circuits

3. HV testing

4. Issues related to cold diodes

5. Related to CSCM (thermal amplifier)

6. Others

7. Not discussed

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Nr Circuits Short description Main Responsible1 All Information library MPE2 All Electrical integration drawings MPE3 All Peak DC voltage check MPE

4 All E-model (e.g. PSPICE), transient voltage, effects of faults MPE 5 All Hot spot temperature MPE 6 All Ground insulation current monitor EPC7 All Periodic automatic test of insulation MPE8 All Protection resistors for V taps MPE / MSC9 All In-situ test plan for circuits not tested to full load MPE

10 All Test simultaneously main and corrector circuits MPE11 RB Diodes: qualify design or engineer repair solution MPE / MSC12 RB/RQ Internal voids in T connection to diodes MPE13 RB/RQ Improve spider insulation MSC14 RB/RQ Consolidate main splices MSC15 RQ Diodes: qualify design or engineer better solution 16 17 IT Define repair plan MSC18 IT Test & document splices MPE19 6kA Quench studies MPE20 Cur Leads Redundant temperature sensors in safety chain CRG / MPE21 Cur Leads Top temperature sensors in safety chain CRG / MPE22 Cur Leads Risk of electrical breakdown due to He leaks MSC23 DFB Repair 13kA splices or prove them healthy MSC / MPE24 DFB BB deflection studies MSC

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Documentation (1+2)

Objective: documentation of LHC for the next 20+ year. Should be done within the next year(s), to capture as much information as possible, since it becomes more and more difficult. An easy access to the data is equally important.

• What exists?

• What needs to be done?

• What needs to be documented?– Individual magnets (fabrication drawings, test results, …)

• e.g. mechanical drawings of the latest version installed in LHC (magnets)

– Current leads (fabrication drawings, test results, …)– Electrical circuits (in particular drawings for sc circuits, with details)– Auxiliary equipment (e.g. diodes, QPS electronics, …)– ROXY field model for magnets are required for quench calculations (possibly

also including input files)– PSpice models and results of calculations

……. this list is not exhaustive

3

QPS documentation in EDMS

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Example for the documentation of one system: QPS is doing very well, however, EDMS tree with entries for departments is not convenient – should be related to LHC

Layout database for electrical circuits

• Electrical circuit are well described in the database and now also in integration drawings. To fully exploit the potential, and to validate drawings, both should be coupled

• Entry to find all electrical circuits, in the powering subsectors (8 sectors, 36 powering subsectors)

• Link to information about magnets

• Information about circuits and elements in a circuit (magnets, power converters, warm cables, …)– GENERAL INFORMATION, POWER CONVERTERS, QPS, WARM

CABLES, INTELOCKS, e.g. link to magnet catalogue

• Circuit diagram, coded in XML, with details of all elements that carry current, including complex circuits such as RQX

• Not inside the database: voltage taps, other auxiliary equipment, ….

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Layout database for electrical circuits

• Electrical circuits today integral part of LHC Layout DB– Powering Subsectors, Circuits, NCs & ECRs, HWC Tests, Magnets, Systems,

circuit description…

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In the electrical database…reminder

• All information of about 70000 interconnections are stored in the DB.

• The required information for each interconnect was downloaded and used to make and test the interconnects.

• Not a single failure was detected (this would have not been possible with only the use of drawings).

• The information is also being used in the LHC control system.

Drawings for electrical circuits (S.Pemberton & K.Pereira)

• Electrical drawings done in AUTOCAD.

• All 8 sectors graphically complete.

• Many upgrades to the existing drawings from 2004+ including:– Cryogenic instrumentation to magnet internals and IFS box– Detailed illustrations above each DFB of current lead voltage tap and

temperature sensor routing– Illustrations above each DFB of the physical layout of the DFB modules in the

tunnel

• Legend from the original electrical schematic were added.

• Not yet completed– Additional small upgrades required to bring the drawings in line with legends.– Non - conformities and QPS signals still to be added.– Verification….– Also required for addressing quench propagation: variation of cooling

conditions due to different insulation (number of layers of insulation), helium conditions (liquid at 1.9K or 4.3K, gaseous).

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Drawings for electrical circuits

• Each sector needs to go through a preliminary check before being released to the individuals involved in the approval process:– initial crosscheck performed using the various forms of reference information

extracted from EDMS/CDD.– sector 1-2 & 2-3 was reviewed and is ready for release. – already there are various anomalies between different sources of official

documentation.

• Validation still pending (huge work), idea to couple the validation it with a digitalisation of the information (get information into layout database for electrical circuits).

• A spread sheet of these anomalies will become available, which will then be given to the approvers for their review.

• Already before final approval, it is now up to the users to start trying out the drawings and to give comments…

9S.Pemberton & K.Pereira

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Example: one entire LHC sector (sector 1-2)

S.Pemberton & K.Pereira

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First zoom

S.Pemberton & K.Pereira

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Second zoom

S.Pemberton & K.Pereira

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Third zoom

S.Pemberton & K.Pereira

Long term documentation…

• Tremendous amount of information electronically available

• Circuit drawings have been completed

• Sometimes the info is there, but users do now know how to find the data

• Easy access to the information is required (possibly from one central entry)

Suggestion for two actions:

1. A small working team should define the further work, and come up with a global view to ensure a correct integration of all information in the system. This must be in collaboration between MPE, MSC, EDMS, database experts, and others.

2. Starting from the circuit drawings, the same information should be captured in a database, this will allow automatic checking of a large fraction of the information – the proposal needs to be finalised.

This is an activity that will take several years, possibly until end of LS1

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Circuit modelling (3+4+5+19)

• To check peak voltages, transient voltages during quench, hot spot temperatures in case of non-conformities such as one of the heaters does not fire, to validate thresholds of the quench protection system

• To address electromagnetic waves in the circuit (in particular for RB and RQ circuits) during discharge or failure conditions

• These studies should also address the question of quenches in MQM and MQY

• ROXIE field model for magnets is required for quench calculations

• One concern is repair and downtime of LHC due to damage of the superconducting magnet system

• One concern is the availability of operation (e.g. thresholds should be set correctly, neither optimistic nor pessimistic)– 50% of beam dumps above injection energy are related to the powering

system (incl. Cryo, QPS, PCs, …)

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Circuit modelling

• Electrical models with PSPICE– in PSpice quenching is introduced by an Electro-Thermal model. Quench

propagation velocity is a parameter and relies on experimental data or other models (error ~1% if experimental data are available, otherwise ~10%)

• PSPICE models have been developed for nearly all circuit types

• Coupled electrical / thermodynamics models with QP3 (Arjan Verweij), COMSOL and ROXIE– such approach can give quench propagation and correct hot spot

temperatures

• The models are prepared, tested and compared with some experimental data. When questions come up, reaction can be fast (such as the AUG event on the dipole magnets)

• From past experience: more than 80% of all issues are related to the main dipole and quadrupole circuits

• It is not possible to address in simulations all possible failure cases for all electrical circuits

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PSpice Simulation – Electro-Thermal model

Electrical circuit• Power converters• Resistances• Inductances• Diodes

After quench: Ohmic heating of magnets

Changing cable temperature

Changing cable physical properties

• Electrical resistivity• Thermal capacity• Thermal conductivity

Cable magnetic field depending on the current flowing through them

Magnet inductance depending on the current flowing through its cables

Circuit modelling

• Quench calculation were performed for MQM and MQY recently, to defined the threshold for the quench detectors, being published in a note

• Calculation of thresholds for the main bus bar quench detectors, as well as for other magnets

• Progress for circuit modelling in PSpice:

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• All different circuit types above 120 A circuits are modelled (RB, RQF/D, IPQ, IPD, 600A)

• One corrector magnet for 120 A was partially modelled

Circuit type Circuit EE

13 kA RBRQ

YesYes

IPD RD2 No

IPQ RQ4RQ10

NoNo

Inner triplet RQX No

600 A RQSRQTL9 & 11

NoYes

80 A RCBYH No

Strategy for circuit modelling

1. Models the electrical circuit in PSPICE and the magnet with QP3

2. Validate the model with simulations and comparison with experimental data

3. Apply the model to a few failure cases

4. Document the results, ensure availability of the model in case it is required to understand LHC performance

5. Run the model in case of need

Examples:

• Quenches of main dipole magnets after a failure in the electrical main supply

• Model of the electrical circuit of the inner triplet circuit

• Voltage thresholds for IPQ circuits with MQM magnets to establish threshold in the quench protection system

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RQX modelling (simplified drawing)

20S.Rowan

Power Abort without firing heater

21S.Rowan

Quench of a magnet, all quench heaters fired

22S.Rowan

PSpice Simulations: Failure of FWT Triggering

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Failure of triggering the FWTs results in a potentially dangerous 3.5kA current flowing in reverse bias through the RTQX2 diodes.

Note the positive current in the FWT path is merely the RQX PC crowbar and not the FWTs themselves.

S.Rowan

RQX modelling case studies

• Quench simulations at nominal / full current

• FPA / Quench simulations with all three PCs active at all current ranges

• “Failure” simulations (e.g. FWT not triggering during quench / Magnet Shorts)

• Results analysis using PSpice trace plotting software. This includes:– Energy stored (1.6-1.8MJ@nom) and dissipated within the magnets (~95+%) – Energy dissipated in all other circuit components (<5%) – Temperature within the magnets (~60-85K@nom) – Resistance of magnets during quench (~210-790mΩ@nom)

• As well as numerous other options…..

24S.Rowan

RB circuit case study, event on 14/5/2011

• LHC at injection current, no ramp, pilot beam in LHC

• Activation of an emergency stop (switch failure), loss of 18 kV

• RB power converters in sector 12 and sector 23 followed a wrong reference voltage. But no interlock was generated (thyristors not fired)

• 22 ms after 18 kV loss an earth fault was detected in power converters. Only then were the thyristors of the power converter’s crowbar fired

• Large oscillations of the voltage measured at the output of the power converter and significant change of magnet current

• For nine dipoles, QPS threshold was exceeded and heaters fired

• For one dipole, the symmetric quench detection kicked in and fired quench heaters (reference lost)

• At 450 GeV, minor consequences (quick recovery of cryogenics). At 3.5 TeV, the consequences would have been more severe

• Beam dumped after a trigger from interlock systems (no impact on beam before beam dump)

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RB circuit case study

• A Fast Power Abort is triggered.

• Normally the thyristors of the crowbar fire and conduct the current, this did not happen. The path for the current is the capacitive branch of the PC filter that is charged. The voltage across the PC reaches high negative values (~ -150V), the current decreases with high ramp-rate (~ -15A/s).

• After 22 ms, the thyristors are fired. The current starts to flow through the crowbar. A current flows back and forth between the inductors and the capacitors of the filter, which is discharging. A wave is generated and travels along the dipole chain.

E.Ravaioli 26

Analysis of the origin of the heater firings on 14.05.2011 in RB.A12 and RB.A23 following spurious AUG in TI2, E.Ravaioli; M.Zerlauth; H.Thiesen, EDMS 1159315

Current in the RB circuit

E.Ravaioli 27

Difference of voltage signal across the apertures for dipole B19L2 in sector 12

E.Ravaioli 28

Maximum amplitude of the aperture voltage difference during PC switch off

E.Ravaioli 29

Individual powered quadrupole magnets

• RQ5-RQ10 circuits contain MQM magnets with different lengths, 2.4m (MQMC), 3.6m (MQM), and 4.8m (MQML). The RQ4 circuits contain MQY magnets and are also considered.

• Especially the RQ10 circuits have tripped several times during the LHC operation in 2010 and 2011. Can the number of spurious trips be reduced by increasing the QPS threshold voltage or by increasing the discrimination time?

• Calculations were performed for RQ7-RQ10, operating at 1.9K. RQ5-RQ6 operate at 4.5K, with about 20% smaller current and are therefore much safer.

30A.Verweij

Calculation methods…

• t=0 Start local normal zone and voltage rise

• t=tthr Voltage rise reaches threshold (U=Uthr)

• t=tthr+tdiscr QPS triggers, U>Uthr for a time equal to

tdiscr

• t=tthr+tdiscr+Dth Firing heaters. Dth is usually a few ms

• t=tthr+tdiscr+Dth+Dtdiff=tres Start of the global resistive zone due to

the heat from the heaters diffusing into the coils

• The Miits after tre are taken from the data recorded from 15 quenches

0

0.5

1

1.5

2

2.5

3

3.5

0 1000 2000 3000 4000 5000 6000

MIIt

s' [1

06A

2 s]

Current [A]

• Simulation are performed with QP3

• Realistic or pessimistic parameters are used (e.g. RRR=100)

31A.Verweij

First results … need to be validated

• An increase of the QPS threshold up to 400mV for RQ5-RQ10 circuits is safe for currents up to 5kA, the hot spot will remain below 350K.

• For operation at nominal current (5390A) an increase in threshold is still safe if limited to 200mV maximum.

• At ultimate current the hot spot temperatures might increase to quite high values of 530K, even for present QPS settings (Uthr=100mV, tdiscr=10ms).

An increase in threshold should therefore be avoided.

Current [A] Field [T] Uthr [mV] tdiscr [ms] MIIts [106 A2s] tthr [ms] Thot [K] 5820 6.565 100 10 4.055 1.2 532 5820 6.565 200 10 4.105 2.7 551 5820 6.565 300 10 4.156 4.2 571 5820 6.565 400 10 4.214 5.9 593 5390 6.080 100 10 3.678 1.6 402 5390 6.080 200 10 3.739 3.7 420 5390 6.080 400 10 3.858 7.8 457 5000 5.640 100 10 3.310 2.4 303 5000 5.640 200 10 3.375 5 318 5000 5.640 400 10 3.510 10.4 351 4000 4.512 100 10 2.403 5.2 150 4000 4.512 400 10 2.690 23.1 185 2000 2.256 100 10 1.739 44.8 83 2000 2.256 400 10 2.184 156 111

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ElQA (7+10)

• Checking voltage withstand between circuits is part of Electrical Quality Assurance

• Circuits are regularly tested according to EDMS procedure 788197 (issued early 2008), conditions such as temperature is taken into account– tests being done at least once per year, after Xmas shutdown– describes a full workflow and defines tests that need to be done

• Document 788197 is being updated. Several changes are being done:– add possible test scenarios– update requirements for cryogenic conditions for each circuit and type of test– some tests need to be extended (e.g.: diode turn-on voltage measurement)– update voltage withstand criteria for all circuits (preliminary version prepared

by Nuria Catalan-Lasheras being validated)– check known weakness on the level of lemo connector on 120A circuits

• An ElQA campaign with updated parameters should be done before LS1, to validate and possibly consolidate circuits during LS1– comments?

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ElQA team

ElQA

• Each circuit is tested versus ground, all other circuits grounded

• Dipole lines (go and return) are tested separately, since the circuit can be interrupted at the level the warm cable connection

• Tests of the two bus-bars of RQ together, the bus cannot be interrupted

• Specification that was used for all tests is EDMS 90327

• In the future, maximum operational voltage against any neighbouring circuit is taken into account– Which electrical circuits have bus-bars running in the vicinity?– Consider nested circuits– Maximum operation voltage x 1.2

• Tests are already partly automated. It is considered not reasonable to fully automate these measurements (would require high current switches and compromise safety)

• Tests for validation of circuits for realistic operational parameters, not always to full load (possibly different strategy before LS1)

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ElQA

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Tested Max op. voltage Proposed voltage level3.5 TeV 7 TeV

MB 1900 450 487.5 1900MQ 240 376.5 520.1 650MCS 480 376.5 840 1000MCD 480 339.5 840 1000MCO 480(200) 199.5 420 480 (200)MS 600 399 840 1000MSS 600 301 840 1000MO 600 406 840 1000MQS 360 399 840 1000MQSx 360 399 840 1000MQ6 360 399 840 1000MQTL(9) 360 399 840 1000MQTD/F 360 406 840 1000IPQ (1.9K) 480 266 420 480IPD 600 600 600 600MCB 600 (200) 600 (200)Undulator 500 500

Splice resistances for high current magnets (18)

• The measurement of splices for all individually power high current quadrupole magnets is completed (IPQs,78 magnets).

• Same for individually power high current dipole magnets (in total 12 IPD 12 magnets, except D3.L4 and D3.R4 still to be done).

• The worst largest resistance has been seem for RQ10, RQ9, RQ8 (because of noise picked up by long cables) - pessimistic values.

• All splices measured seem to be correct.

10 nOhm

1 nOhm

36R.Mompo, G.d’Angelo

Splice resistances for DFBXs power magnets

• Same system as already used on IPDs, IPQs and QPM.

• 2 systems are being prepared in order to be able to measure 2 DFBXs at a time (still some cabling to be done)

• The DAQ is based on a PXI crate equipped with 7 or 9 high precision DVMs.

• Tests planned during this Xmas break.

• Measurements will be done with the system in front of DFBXs, for maximum precision and because of availability of diagnostic connectors.

• Circuit RQX/RQTX2 will be powered together with a pyramid.

• D1 magnet will be measured separately.

37R.Mompo, G.d’Angelo

ISRM status for DFBXs

R.Mompo, G.d’Angelo

Other recommendations (8, 20, 21)

• 6 ground insulation current monitor: not MPE but EPC, seems to be difficult for all circuits ….

• 11,12, 15: dedicated presentation on diodes ….

• 20: Redundant temperature sensors of current leads (50K) in safety chain– second temperatures should be made available– use of the two temperature sensors to be discussed, risk for damage and

availability to be considered, possibly not the same solution for all circuits

• 21: Temperature interlock on the top should be redundant and used in the safety chain.– Installation of thermo-switches on going –connected to the “safety chain”

(power converter). To be completed during LS1.– For the experience with these switches the need for redundant equipment is

questioned – risk for damage and availability to be considered, possibly not the same solution for all circuits

• 22: Not considered to be a risk since the current leads are operating in gaseous helium (risk of electrical breakdown in helium)

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RB and RQ circuits: earth voltage feelers type DQQDE

• The earth voltage feelers are integral part of the enhanced layer of the LHC quench protection system commonly referred to as nQPS. The system serves for enhanced circuit diagnostics and will monitor the electrical insulation strength of the LHC main circuits especially during fast discharges (LHC-DQLPU-EC-0001, EDMS:1153884)

• The system allows the remote supervision of the electrical insulation strength during LHC operation without accessing the LHC tunnel.

• As all data will be stored in the LHC logging database also the evolution in time can be studied. In case of an eventual earth fault the system will allow to identify the location of the fault position on the half-cell level.

• This will significantly reduce the occupation time in the LHC tunnel of the teams in charge of the precise localisation repair.

40R.Denz

Earth voltage feelers type DQQDE

• Per sector a maximum of 54 devices for the main dipole circuit and 55 for each of the main quad circuits can be installed (1308 units in total).

• The installation and commissioning will be staged starting in 2012 with one sector and being completed during LS1

41R.Denz

CSCM - thermal amplifier (9+23)

• The thermal amplifier technique has been developed successfully and tested in SM18. It is believed that it can be done without compromising the safety of the circuits.

• For the time being, no tests are planned for the Xmas stop 2010-2011. If required, such tests can also be performed later.

• It is considered that these tests fully qualify the interconnects in the DFB.

• The proposal to tests at 6kA differs from the initial proposal (HP), to test at full current. This allows to use the RB power supply.

See presentation of H.Thiesen

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Diodes (11+12+15+25)

• Dedicated presentation on diodes ….

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Consolidation of interconnects (13+14)

• Improve spider insulation

• Consolidate splices

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Conclusions

• Documentation: considered to be very important, lot of progress, needs to be continued and coordination between teams is required.– Long term commitment, needs to be supported by management since this is

resource intensive– Could members of the Task Force help?

• Simulation work and comparison with measurements: lot of progress, to be continued, in particular we need to identify when PSpice, QP3, COMSOL and ROXIE are to be used.

• This work is being done to a large extent by Fellows and Students – coherent documentation of models and results is a key issue. It should be coupled to the documentation discussed above.

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Conclusions

• What questions do we have today?– can we damage electrical circuits during operation, with and without beam

(taking into account realistic currents in the circuit during beam operation….)– do we need to consolidate circuits during the long shutdown (apart from RB

and RQF/D)?– can we avoid tripping of circuits during (beam) operation?– can we relax the QPS threshold, and under what circumstances?

• Whenever we add interlocks, a risk analysis is required that takes into account risk (probability of a failures * consequences) and the availability (downtime due to interlocks)

On-going work and plans for the future

• Work on documentation

• Circuit modelling along the lines presented

• Tests of the electrical circuits before LS1

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