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Transcript
Update on the analysis of the event of 14th May 2011 Emmanuele Ravaioli Thanks to M. Zerlauth, G. Cumer, H. Thiesen, Z. Charifoulline, A. Verweij TE-MPE-TM 18-08-2011 Event of 14th May 2011 Sequence of events Impact on the QPS Emmanuele Ravaioli Short and mid-term actions TE-MPE-TM 18-08-2011 Long-term actions 2 Event of 14th May 2011 Impact on the QPS Sequence of events 1. LHC at injection current, no ramp, pilot beam in LHC, power converters supply 760 A in steady state. 2. AUG triggering due to a defective AUG switch. 3. Loss of the 18 kV network around BA7, SMI2 and LHC point 2. 4. RB power converter trip in Sector 12 and Sector 23: PCs followed a wrong reference voltage. But no PIC signal was generated. 5. Voltage across the power converters of both sectors decreased up to ~ -152 V, the filter at the PC output charged up. 6. Earth fault detected in the power converters (21 ms after the 18 kV loss): a PIC signal was generated. 7. Only at this moment were the thyristors of the power converter’s crowbar fired. 8. Current exchange between capacitive and inductive branches of the PC filter, which lead to a substantial change of the magnet current (±0.3 A) and to large oscillations at the output of the power converters. 9. The voltage waves propagated through the dipole chains and caused the triggering of the QPS and the subsequent firing of the quench heaters of 9 dipoles. 10. The heaters of one further magnet were fired by the nQPS (symmetric quench detector) due to lost reference, as the other two magnets present in its crate triggered and fired the quench heaters. Emmanuele Ravaioli TE-MPE-TM Short and midterm actions Long-term actions Chaine AUG vers BA7 Chaine AUG vers UW25 For more info Major Event Report (EDMS document: 1144995) Rapport préliminaire (EDMS document : 1147728) LMC Meeting on 18 May 2011 - TI2 AUG on Saturday 14 May, G. Cumer Review AUG TI2, G. Cumer, 21 July 2011(EDMS document: 1154682) 18-08-2011 3 Event of 14th May 2011 Sequence of events Short and midterm actions Impact on the QPS • The dipoles whose QPS triggered were the ones observed in the past to have apertures with unbalanced impedances, and thus be oversensitive to any voltage wave propagating through the chain. • The incident occurred at injection current and during a plateau (760 A, 0 A/s). At higher current the consequences would have been heavier and lead to a larger number of quenched dipoles. • Two possible worst cases • 2 kA, 10 A/s: The unbalanced dipoles oscillate more when they are ramping around 2 kA. • 6 kA: The quenches are more dangerous for the dipoles. Emmanuele Ravaioli TE-MPE-TM Long-term actions For more info LMC Meeting on 18 May 2011 - HTS quenches and consequences of AUG, R. Schmidt TE-MPE-TM on 28 July 2011 - Event of 14th May 2011 what we understood and what we did not, E. Ravaioli 14.05.2011 – Analysis of heater firings in RB.A12 and RB.A23 following spurious AUG in TI2 (EDMS document: 1157870) 18-08-2011 4 Event of 14th May 2011 Sequence of events Impact on the QPS Short and mid-term actions Long-term actions 1. Incident report 2. Adding the signal from the AUG chain EUB1/2I into the sum signal sent to the powering interlock controllers around IR2 (EN-EL during next technical stop, end of August) (Approval of LMC needed) 3. Improved model of the power converter, same results • Current source → Voltage source • When the 18 kV loss occurred, PCs followed a wrong reference voltage ( ) • Thyristors of the PC switched-off at the moment of the 18 kV loss (gate current to 0) • Thyristors of the crowbar fired only after 22 ms, when an earth fault is detected 4. Establishing whether similar events (no current in the PC branches but no PIC signal sent) may occur in the future, and assessing the consequences (voltage at the output of the PC, firing of the quench heaters) Emmanuele Ravaioli TE-MPE-TM 18-08-2011 5 Event of 14th May 2011 Sequence of events Impact on the QPS Short and midterm actions Long-term actions 1. Modification of the AUG chains of TI2 (and later on TI8) is currently under study by ENEL, to realign current inconsistencies between the powering layout, sector doors and the AUG chains of TI2 and TI8. This modification will allow disconnecting again the upstream parts of TI2/TI8 from the PIC interlock logic, as AUG activations in this zone will not affect LHC powering anymore. (not possible before LS1) 2. Study of alternative and more radical solutions to the problems caused by the voltage waves travelling through the dipole chain (example: Knud’s idea: Changing the earthing point of the RB circuit) Emmanuele Ravaioli TE-MPE-TM 18-08-2011 6 Event of 14th May 2011 Sequence of events Impact on the QPS Short and mid-term actions Long-term actions Chaine AUG vers BA7 Chaine AUG vers UW25 For more info LMC Meeting on 18 May 2011 - HTS quenches and consequences of AUG, R. Schmidt For more info Major Event Report (EDMS document: 1144995) Rapport préliminaire (EDMS document : 1147728) TE-MPE-TM on 28 July 2011 - Event of 14th May 2011 - what we understood and what we did not, E. Ravaioli 14.05.2011 – Analysis of heater firings in RB.A12 and RB.A23 following spurious AUG in TI2 (EDMS document: 1157870) LMC Meeting on 18 May 2011 - TI2 AUG on Saturday 14 May, G. Cumer Review AUG TI2, G. Cumer, 21 July 2011(EDMS document: 1154682) Emmanuele Ravaioli TE-MPE-TM 18-08-2011 7 Event of 14th May 2011 Overview of implementation of AUG chains in TI2 Courtesy of G. Cumer Chaine AUG vers BA7 Chaine AUG vers UW25 Emmanuele Ravaioli TE-MPE-TM 18-08-2011 8 Event of 14th May 2011 Explanation of the event 1. The circuit is operating at constant current during injection @ 760 A . 2. A FPA is triggered. Normally the thyrstors of the crowbar should be fired and conduct most of the current, but they fail to conduct. The only path through which the current of the circuit can flow is the capacitive branch of the PC filter, which is charged. The voltage across the PC reaches high negative values (~ -150 V) while the current in the circuit decreases with high ramp-rate (~ -15 A/s). There is no voltage ringing coming from the PC since the inductive branch of the filter is blocked. 3. 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. Emmanuele Ravaioli TE-MPE-TM 18-08-2011 9 Event of 14th May 2011 Dipoles that triggered the QPS – Comparison with a past event – S12 Emmanuele Ravaioli TE-MPE-TM 18-08-2011 10 Event of 14th May 2011 Dipoles that triggered the QPS – Comparison with a past event – S23 Emmanuele Ravaioli TE-MPE-TM 18-08-2011 11 Event of 14th May 2011 Incident Report - Abstract Emmanuele Ravaioli TE-MPE-TM 18-08-2011 12 Event of 14th May 2011 New model of the PC: Voltage at the output of the PC (V_MEAS) Emmanuele Ravaioli TE-MPE-TM 18-08-2011 13 Event of 14th May 2011 New model of the PC: Current flowing in the circuit (I_A) Emmanuele Ravaioli TE-MPE-TM 18-08-2011 14 Event of 14th May 2011 New model of the PC: Voltage difference between the apertures of a dipole (QSO) Emmanuele Ravaioli TE-MPE-TM 18-08-2011 15 Event of 14th May 2011 New model of the PC: Voltage across a dipole (nQPS) Emmanuele Ravaioli TE-MPE-TM 18-08-2011 16 Event of 14th May 2011 New model of the PC: Main current in the circuit Emmanuele Ravaioli TE-MPE-TM 18-08-2011 17 Event of 14th May 2011 Limitation des interdépendances – Propositions EN/EL à valider Courtesy of G. Cumer Emmanuele Ravaioli TE-MPE-TM 18-08-2011 18 Event of 14th May 2011 QSO signal – Comparison between measurements and simulations Effect of the change of the earthing point of the circuit Emmanuele Ravaioli TE-MPE-TM 18-08-2011 19