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Chamonix Workshop XIVSession 4 – Other Issues affecting Beam Commissioning 1

Electrical Quality Assurance (ELQA)

Tuesday, 18th January 2005

Davide Bozzini, AT-MEL-EM

Thanks to S. Russeschuck, F.Rodriguez Mateos, T. Zichler & the HCWG members

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Introduction to the LHC Electrical Quality Assurance (ELQA)

The ELQA activities and LHC operation with beam

Detection of electrical faults

Classification of electrical faults

Diagnostic methods for detection

Examples of electrical faults diagnostic

Acceptance and qualification criteria

Accessibility to the electrical circuits

Sequence and duration of diagnostic activities

Staff experience and familiarity with the LHC machine, resources

The experience of String 2

Conclusion

Outline

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The ELQA activities

A series of actions to ensure the correct functioning of the electrical circuits of the LHC machine

Definition

Define a quality assurance plan to apply to the machine during installation, hardware commissioning and operation

Provide the procedures, tools and resources to perform the necessary checks and tests during ELQA activities

Grant the traceability of checks and tests performed at the different stages

Aim

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The ELQA activities

When

Manufacturing of componentsDFBX, Line N cable,…

Machineassembly

- diagnostic- re-qualification

- Continuity- Polarity- Electrical insulation- Global resistance, inductance- Global insulation- ... ...

- Insulation prior/during/after cool-down - Transfer function- ... ...

Time

Hardwarecommissioning

Operation, Shutdown, repair

- Continuity- Polarity- Electrical insulation

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The ELQA plan

Qualification and preparation before introduction into the tunnel- Surface (cold) tests

- generation of non conformity lists- qualification of individual electrical component

DFBDFBXDFBMDFBA

current leads13 KA7.5 KA600 A60 A

120 A

magnetsdipolesarc sssIR sss

separation dipolesinner triplet

bus bars6 KA

600 A (line N cable)

Specification ofComponents

(Electricalparameters)

EStype of circuitsinstrumentation

Electrical conformityreport

ELQA activities during sub-sector assemblySpecification for

electricalinterconnections

M1 & M2Line N BBinner triplet

Electricalinterconnection

Layouts

ELQA activities of sub-sector circuitsduring hardware commissioning

Traceability ofELQA

documentationgenerated during

assembly andcommissioning

Technicalsupport

- Tools forassembly

-Tools forelectrical

verifications- Tools fordiagnostic

Beam commissioning&

Operation

Tunnel environment

LHC Referencedatabase

Existingelectrical

non-conformities

Generatedelectrical

non-conformities

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ELQA and LHC operation with beam

Though considered unlikely, it’s almost sure that due to the complexity of the LHC machine we will face faults and problems related to the superconducting (SC) electrical circuits during the operation with the beam

A fault affecting a SC electrical circuit can be unpredictably provoked by different sources and, in most cases, it cannot be detected on-line or anticipated

Most of the electrical faults will have a direct impact on the machine availability and/or on the beam quality

Beam Based measurements may require in-situ verification of the magnets polarities (Chamonix X, J-P Koutchouck, Finding a faulty element of the machine)

Motivation

Therefore Efficient postmortem ELQA diagnostic methods to be applied during commissioning and

operation with beam must be established

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Detection of electrical faults

The beam (1)

– Via the BPM’s and after investigation

The power converters (2)

– Over voltage

– Detection of an earth fault

– Monitoring of leakage current

The quench protection system (3)

– Loss of instrumentation (Voltage taps)

– Detection of an open circuit

– Consecutive quenches in a given half/cell

During the ELQA activities (4)

– Measured electrical characteristics after a shut down period or re-commissioning out of specified parameters

Except for (1), practical experience acquired during hardware commissioning will be available

Sources for electrical faults detection

Events that may launch an ELQA

diagnostic intervention

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Classification of the electrical faults (some examples)

Fault Consequence Detection Diagnostic method

Inverted polarity of a magnet within a series (ex: MCS)

Beam quality- BPM’s- Beam observations

- Polarity check

Open circuit of a main circuit

Beam abort- QPS- Power converter

- Continuity check- Transfer function

Short to ground of a main circuit

Beam abort - Power converter- High voltage test- Transfer function

Loss of instrumentation used for magnet protection

Beam abort - QPS- Continuity check- TDR

…………….. ………………. …………………… …………………

The notorious one’s

The malicious one’sFault Consequence Detection Diagnostic method

Quench of bus bar segments or splices

Beam abort - QPS ?

Transitory shorts to ground or between circuits

Beam abort - Power converters ?

High ohmic resistance of bus bar interconnect

?- QPS- Cryo system

…………………

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Diagnostic tests (1)

Diagnostic test Applied to Method

Electrical insulationsegment - ground DCV supply

segment - segment I leakage

Capacity Circuit - groundDCV

Measurement of C

Continuitysegments DCA supply

Circuit Closed loop

Polaritysegments DCA supply

Circuit Voltage drop via V_taps

Instrumentation Current lead V_tapsDCA supply

Voltage drop via V_taps

Diode polarity MB,MQ diodesACV supply

Turn on voltage

Transfer functionCircuit Z(f)

Circuit - ground Z(f)

For the notorious faults

Wide experience acquired during machine assembly and hardware commissioning

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Diagnostic tests (2)

For the malicious faults

All tests of the previous slide are applicable but probably not enough

Several ideas on the air, some of them already tested

– Time domain Reflectometry + high voltage pulse

– High voltage partial discharge

– Specific hardware to be locally and temporarily installed during operation in order to get detailed information about transitory faults

– Power dissipation measurements to localize ohmic resistances (require collaboration with cryogenic specialists)

– ……………………..

A systematic approach will be difficult to be applied

Experience will only be acquired on field when such faults will arise

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Electrical fault diagnostic (1)

Ga

in/

rea

l

Ph

ase

/ im

ag

Frequency [Hz]

Ga

in/

rea

l

Ph

ase

/ im

ag

Frequency [Hz]

Transfer function of MQD and MQF string circuits at cold (1.8 K)

– RQF (reference)

– RQD phase(1Hz)= 0º !!

– RQD Z(1Hz)= 6309 ohm

– RQD has a high resistance somewhere, NOT OK

Transfer function of a portion of circuit via the local voltage pick-up instrumentation

– Coils of two MQs (blue and green), OK

– Portion of circuit including three dipoles (red), NOT OK

Transfer function Z(f)

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Electrical fault diagnostic (2)

Progressive powering (without beam) of the SC circuit

Follow-up of temperature trend through the string of magnets

Calculation of the dissipated power by joule effect

Localization of an increase of temperature

Detection of a high ohmic resistance in a MQF circuit

RQF Power dissipation test @ 1.8 K

0.0E+00

5.0E-01

1.0E+00

1.5E+00

2.0E+00

2.5E+00

3.0E+00

27/0

6/20

0310

:00:

00

27/0

6/20

0310

:01:

40

27/0

6/20

0310

:03:

20

27/0

6/20

0310

:05:

00

27/0

6/20

0310

:06:

40

27/0

6/20

0310

:08:

20

27/0

6/20

0310

:10:

00

27/0

6/20

0310

:11:

40

27/0

6/20

0310

:13:

20

Time

Cur

rent

[kA]

,

U_d

iff [V

],

Res

ista

nce

[ohm

]

0.E+00

2.E+02

4.E+02

6.E+02

8.E+02

1.E+03

1.E+03

Pow

er d

issi

patio

n [W

]

Power dissipation

Current

U_diff

Resistance

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Electrical fault diagnostic (3)

Allows to determine the quality of the electrical insulation

Is a qualitative analysis

Requires time and a high practical experience, good feeling and good luck

Partial discharge test of a PS dipole magnet

Courtesy T. Zickler

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Electrical fault diagnostic (4)

Electrical insulation degradationDescription RB [Mohm]

Reference at warm before pump down of phase 3

(2003-03-28)10.1

Reference at cold before pump down of phase 3

(2003-04-28)9.4

Reference at cold after 13 kA circuit problems

8.7

Warm cables connected, cold masses under gaseous helium

10

After warm cable dismantling 14

After cold mass purge and injection of air

29.6

After MRB dismantling 30.8

Separation of Bus Bars in the MRB ext BB int BB

After short circuit dismantling and BB cleaning 31.6 725

After disconnection of RB Bus bars in

between SSS4 and MB4

MB4-to-MB6 13100 9150

DFB-to-SSS4 31.4 16800

Example of the MB circuit of String 2 phase 3

Resistance to ground out of specification but not a firm short to ground

Localization of fault only possible if the circuit can by split in sub circuits (opening of interconnections is needed)

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Acceptance and qualification criteria

Current leakage of a main dipoles (MB) electrical circuit

The power converter will turn off if Ileak > 50 mA (LHC-D-ED-0001 rev 2.0)

By specification (LHC-M-ES-0001 rev 1.1) the maximum current leakage allowed for a MB circuit corresponds to the number of components that composes the circuit (434) times 20uA / component. This gives an Imax < 8.68 mA

Active leakage current detection level is 5 times higher that the maximum leakage accepted in the specification

The leakage may change depending on the machine/circuit conditions. It is essential to store all the measurements during the time to allow analysis and understanding of the variation

Need to define how to deal, in particular at the beginning of the machine operation with measured values between the two limits

Applicable to all 1715 SC circuits

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Accessibility

PS machine “warm”. Electrical circuits are easily accessible and visible

For diagnostics almost all senses can be used: hearing , visual, smell, touch

Warm machine

LHC machine “cold” electrical circuits will not be directly accessible

This picture shows the String 2 phase 1, i.e. 54 meters without access to the circuits. Diagnostic has been a nice exercise. LHC machine will be 2700 m!

Diagnostic may require the local access to the circuit (opening of interconnections).

Cold machine

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Sequence and duration of diagnostic activities

T0

Activity

Diagnostic phase #1

Analisys and decision

Diagnostic phase #2

Intervention repair

Re-qualification

T1 T2 T3 T4 T5 Time

Time for diagnostic phases #1 and #2 - fixed, if the fault is observable

- variable, if the fault is not observable

Time for analysis and decision - variable, and relies on decision makers

Time for intervention and repair - fixed, if the intervention is known

- variable, if the intervention is new

Time for re-qualification - fixed, procedures known from HC

T0

Activity

Diagnostic phase #1

Analisys and decision

Diagnostic phase #2

Intervention repair

Re-qualification

T1 T2 T3 T4 T5 TimeT6 T7

Opening of the machinefor local diagnostics

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Staff experience and familiarity with the LHC machine, resources

Fundamental experience will be acquired during machine assembly and hardware commissioning

Beam commissioning starts in 2007 most of the knowledge will be gone

Success of ELQA activities during beam commissioning need experienced and well trained personnel

0

2

4

6

8

10

12

14

16

18

Q12005

Q22005

Q32005

Q42005

Q12006

Q22006

Q32006

Q42006

Q12007

Q22007

Q32007

Q42007

Time

Nr.

of

pe

rso

n

HNINP collaboration

FSU

Tech. Students

Staff

Assembly Hardware commissioning

Beam commissioningand operation Interventions during beam

commissioning and operation will have to deal with radiation

Staff shall be familiar not only with the ELQA procedures but also with safety rules and tunnel environment

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The Experience of STRING 2

Reference documents

– From String 2 to the Hardware commissioning of the first sector: A challenge?, slides,F. Rodriguez Mateos, LHC days workshop 2003

– F. Rodriguez Mateos, String 2 Report, EDMS

Outcomes related to the ELQA activities

– Time for diagnostic and analysis was largely underestimated

– Several new methods for diagnostic where tested to determine the source of the faults. →some of them described in this speech

– Despite all the effort put into diagnostic and analysis we could not determine what was the fault in a bending dipole magnet

– The beam, the radiation and most of the tunnel environment constraints were not there

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Conclusion

Assuming a successful hardware commissioning, day 1 of commissioning with beam might be successful, nevertheless we must be prepared for diagnostic interventions during the following days, weeks, months

Operation with beam will have an impact on ELQA activities. Access, safety, radiation rules shall be respected

The detection of faults will be done by different systems (PC, QPS, BPM’s,…). Exchange of information, collaboration is essential

Be ready for unpredictable faults requiring hard interventions (opening of interconnections)

Resources: Experience acquired during hardware commissioning is not granted for 2007 and later. A sufficient number of CERN staff specialists supported by the extension of the HNINP collaboration (motivated now by the need of personnel during beam commissioning and operation) shall be considered

On call service 24/24 and 7/7 seems to be necessary. Not foreseen at the moment

String 2 was an excellent exercise. A sector test with beam would be a must for optimization of ELQA diagnostic activities