1. D. Bozzini, AT/MEL/EM, Chamonix Workshop XIV, January 2005 1 Chamonix Workshop XIV Session 4 – Other Issues affecting Beam Commissioning 1 Electrical Quality Assurance (ELQA) Tuesday, 18 th January 2005 Davide Bozzini, AT-MEL-EM Thanks to S. Russeschuck, F.Rodriguez Mateos, T. Zichler & the HCWG members

2. D. Bozzini, AT/MEL/EM, Chamonix Workshop XIV, January 2005 2  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

3. D. Bozzini, AT/MEL/EM, Chamonix Workshop XIV, January 2005 3 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

4. D. Bozzini, AT/MEL/EM, Chamonix Workshop XIV, January 2005 4 The ELQA activities When Manufacturing of components DFBX, Line N cable,… Machine assembly - diagnostic - re-qualification - Continuity - Polarity - Electrical insulation - Global resistance, inductance - Global insulation -...... - Insulation prior/during/after cool-down - Transfer function -...... Time Hardware commissioning Operation, Shutdown, repair - Continuity - Polarity - Electrical insulation

5. D. Bozzini, AT/MEL/EM, Chamonix Workshop XIV, January 2005 5 The ELQA plan

6. D. Bozzini, AT/MEL/EM, Chamonix Workshop XIV, January 2005 6 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

7. D. Bozzini, AT/MEL/EM, Chamonix Workshop XIV, January 2005 7 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

8. D. Bozzini, AT/MEL/EM, Chamonix Workshop XIV, January 2005 8 Classification of the electrical faults (some examples) FaultConsequenceDetectionDiagnostic 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’s FaultConsequenceDetectionDiagnostic 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 …………………

9. D. Bozzini, AT/MEL/EM, Chamonix Workshop XIV, January 2005 9 Diagnostic tests (1) Diagnostic testApplied toMethod Electrical insulation segment - groundDCV supply segment - segmentI leakage CapacityCircuit - ground DCV Measurement of C Continuity  segments DCA supply CircuitClosed loop Polarity  segments DCA supply CircuitVoltage drop via V_taps InstrumentationCurrent lead V_taps DCA supply Voltage drop via V_taps Diode polarityMB,MQ diodes ACV supply Turn on voltage Transfer function CircuitZ(f) Circuit - groundZ(f) For the notorious faults  Wide experience acquired during machine assembly and hardware commissioning

10. D. Bozzini, AT/MEL/EM, Chamonix Workshop XIV, January 2005 10 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

11. D. Bozzini, AT/MEL/EM, Chamonix Workshop XIV, January 2005 11 Electrical fault diagnostic (1) Gain/ real Phase / imag Frequency [Hz] Gain/ real Phase / imag 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)

12. D. Bozzini, AT/MEL/EM, Chamonix Workshop XIV, January 2005 12 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

13. D. Bozzini, AT/MEL/EM, Chamonix Workshop XIV, January 2005 13 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

14. D. Bozzini, AT/MEL/EM, Chamonix Workshop XIV, January 2005 14 Electrical fault diagnostic (4) Electrical insulation degradation Description 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 dismantling14 After cold mass purge and injection of air 29.6 After MRB dismantling 30.8 Separation of Bus Bars in the MRBext BBint BB After short circuit dismantling and BB cleaning 31.6 725 After disconnection of RB Bus bars in between SSS4 and MB4 MB4-to-MB6131009150 DFB-to-SSS431.4 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)

15. D. Bozzini, AT/MEL/EM, Chamonix Workshop XIV, January 2005 15 Acceptance and qualification criteria Current leakage of a main dipoles (MB) electrical circuit  The power converter will turn off if I leak > 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 I max < 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

16. D. Bozzini, AT/MEL/EM, Chamonix Workshop XIV, January 2005 16 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

17. D. Bozzini, AT/MEL/EM, Chamonix Workshop XIV, January 2005 17 Sequence and duration of diagnostic activities  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 Opening of the machine for local diagnostics

18. D. Bozzini, AT/MEL/EM, Chamonix Workshop XIV, January 2005 18 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 Assembly Hardware commissioning Beam commissioning and 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

19. D. Bozzini, AT/MEL/EM, Chamonix Workshop XIV, January 2005 19 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

20. D. Bozzini, AT/MEL/EM, Chamonix Workshop XIV, January 2005 20 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