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OCTUPOLE CIRCUITS

Roberto Lopez & Davide Tommasini CONTENT: MCO magnets Circuit & power converter Integration and routing of wires Commissioning & operation Dielectric tests Splices Faults Strategic questions Conclusion. OCTUPOLE CIRCUITS.

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OCTUPOLE CIRCUITS

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  1. Roberto Lopez & Davide Tommasini CONTENT: MCO magnets Circuit & power converter Integration and routing of wires Commissioning & operation Dielectric tests Splices Faults Strategic questions Conclusion OCTUPOLE CIRCUITS

  2. Design : superconducting, nested inside the MCDs Manufacture : 616 India (Crompton + CAT) + 616 UK (Tesla) Tests : all tested up to 150 A at 4.5 K THE MAGNETS

  3. 0.73x0.38 mm THE MCO UNITS middle of the coil US weld 1.47x2.28 mm 3 (internal)+2 (external) US welds + 2 soldered on MB + 2 US for interconnections

  4. Vtap MCO spool 1 spool 12 A B THE CIRCUIT spool 2 spool 11 MCO A B DFBA DFBA MBB MQ MBA LOW CURRENT HIGH CURRENT • 420 interconnection + 154 MB (soldered) + 385 internal (US) = 959 splices/circuit • measured “average” splice resistance @ 1.9 K ~12 n (Nuria Catalan) : too high? • inductance per circuit ~ 31 mH (77 magnets), energy stored @ 100 A : 154 J • resistance at 300 K of one magnet ~ 3 

  5. 83 m THE POWER CONVERTER LHC 120A-10V http://te-epc-lpc.web.cern.ch/te-epc-lpc/converters/lhc120a-10v/general.stm In case of fault (quench, Iearth > 50 mA during > 20 ms, open circuit ...) the Pwr Module stops and the crowbar switches on when V > 13 V many thanks to Yves Thurel and Valérie Montabonnet

  6. INTEGRATION

  7. INTEGRATION/ROUTING

  8. PROXIMITY TO GROUND

  9. ROUTING IN THE MQ

  10. DIELECTRIC TESTS OF MCO: MAGNETS

  11. DIELECTRIC TESTS OF MCO: INTERCONNECTIONS 120 V ! 240 V ! TP4B:after flushing TP4D:@ 80 K TP4E:@ 1.9 K

  12. HARDWARE COMMISSIONING & OPERATION • All circuits checked to 100A during hardware commissioning 2008-2009 • RCO.A78B2: From HWC 2008 (NC1029807 & NC809944) , first event was a short circuit to ground during HV tests at 560 V, thereafter 3 consecutive quenches at 55 A • RCO.A81B2: From HWC 2009 (NC955048), first observation was a too high resistance, thereafter an open circuit between B12L1 and B11L1 • Currentspresentlyapplied in RCO circuits for operationat 3.5GeV • RPLB.UA23.RCO.A12B1: 23.45 A RPLB.UA23.RCO.A12B2: -32.88 A • RPLB.UA27.RCO.A23B1: -48.01 A RPLB.UA27.RCO.A23B2: 31.35 A • RPLB.UA43.RCO.A34B1: -41.01 A RPLB.UA43.RCO.A34B2: 31.09 A • RPLB.UA47.RCO.A45B1: -37.29 A RPLB.UA47.RCO.A45B2: 27.77 A • RPLB.UA63.RCO.A56B1: 21.72 A RPLB.UA63.RCO.A56B2: -31.79 A Not powered since the 8th of August 2010. Power module changed the 1stsept. • RPLB.UA67.RCO.A67B1: 28.54 A RPLB.UA67.RCO.A67B2: -41.75 A • RPLB.UA83.RCO.A78B1: 9.57 A RPLB.UA83.RCO.A78B2: 0 A Not powered since the 12th of July 2010 . Power module changed the 19th July • RPLB.UA87.RCO.A81B1: -42.53 A RPLB.UA87.RCO.A81B2: 0 A many thanks to Sandrine Le Naour

  13. THE SPLICES long term performance: see C. Scheuerlein also see: N.Catalan“Overview of all superconducting splices in the LHC machine”, Chamonix 2010,

  14. quench • short circuit to ground • open circuit • short circuit to/from another circuit • Case 1. • The maximum voltage remains well below 100 V. • Case 2. and 3. • The stored energy is only 154 J. • Damage should remain localized to the circuit itself. • Furthermore, TE-CRG experts recall this small energy would hardly be noticed by the instrumentation of the cryogenic system. • Case 4. • Involved energies may become relatively large (24 MJ if MQs are involved). • Probably too pessimistic to consider MBs being affected (E~1236 MJ) FAULTS

  15. ARE DEFECTIVE SPLICES PRESENT IN MCO CIRCUITS? if Rs>10 n means defective CERTAINLY YES CAN WE LOCALIZE THEM? major defects YES, by an appropriate campaign through voltage taps STRATEGIC QUESTIONS SHALL WE EXPECT FAILURES OF MCO CIRCUITS? we already had 2 cases during HC, not fully understood yet separation to ground and to other circuits is questionable WHAT WOULD BE THE CONSEQUENCES? light if restricted to MCO, heavier if concern other circuits if limited to MCO circuits worst case is the replacement of a MB-MQ performance of the LHC with one or more MCO circuits provisionally off ? SHALL/CAN WE IMPROVE THE SITUATION? understand: circuit analysis for typical faults monitor: use voltage taps during shut-down checks test: review HIPOT test levels & procedures enhance: critical points are inside the cold mass ...

  16. Findings • Faults already happened • The energy stored in the MCO circuit is extremely low • During HC each circuit was HIPOT tested to each other • The circuit resistance measured from the DFBA looks high (~12 n/splice) • Physical separation to ground and between circuits is questionable • Test levels were (and are) probably on the low side • Power converters look sound • Desirable (within the feasible) actions • Review HIPOT test levels and procedures at warm and before start-up • Perform a measurement campaign of splice resistances, with help of Vtaps • Perform a circuital analysis of reasonable fault scenarios CONCLUSION

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