1. AT-MEL-PM, R. Denz, CERN, CH-1211 Geneva 23 1 QPS system and its risks  Principal risks  General remarks  Quench heater circuits  Quench detection electronics  QPS controls

2. AT-MEL-PM, R. Denz, CERN, CH-1211 Geneva 23 2 QPS system and its risks – principal risks  Electrical safety and the QPS system – principal risks –Charging voltage and stored electrical energy of the quench heater power supplies 6200 power supplies installed in LHC –Electrical potential of the superconducting circuits All quench detection systems galvanically connected to superconducting circuits  Don’t forget … –All QPS electronics fed by 230 V AC UPS

3. AT-MEL-PM, R. Denz, CERN, CH-1211 Geneva 23 3 QPS system and its risks – general remarks  All QPS electronics is protection class 1, low voltage B –Housing conducting and connected to protective earth (PE) –Operational voltages up to 1 kV DC  All QPS electronics is protected against contact (according EN 60529) –IP20 (detectors) or IP30 (quench heater power supplies) –No risk to touch live parts of the installations as long as you: are not E.T. … follow the rules don’t disconnect or cut the respective cables don’t open QPS electronics, distribution boxes, Instrumentation Feed-through System (IFS) boxes while systems are powered don’t flood the QPS installations

4. AT-MEL-PM, R. Denz, CERN, CH-1211 Geneva 23 4 QPS electronics – quench heater circuits I  Quench heater circuits –Used within protection of MB, MQ, insertion region magnets and inner triplets –900 V DC between poles, ±450 V DC to earth (PE) –Note: a quench heater power supply stores 2.9 kJ of electrical energy –Once charged (i.e. QPS-IST @ cold is finished) the quench heater power supplies may discharge into the quench heaters installed in the magnet cold mass at any time Unless there is a specific request to switch off all quench heater power supplies stay charged (until they break or the de-commissioning of LHC …) MB protection rack Quench heater power supplies Q4.L8

5. AT-MEL-PM, R. Denz, CERN, CH-1211 Geneva 23 5 QPS electronics – quench heater circuits II  Quench heater circuits - main magnets (MB and MQ) –Quench heater power supplies DQHDS installed in the yellow racks underneath the main dipoles (also for MQ protection) MB: 4 x DQHDS MQ: 2 x DQHDS –A single cable connection integrating coil instrumentation and heater circuits to IFS box with a single connector to the protection rack Rupture of this connection with powered protection systems will cause discharge MB IFS box connection MB protection rack connection

6. AT-MEL-PM, R. Denz, CERN, CH-1211 Geneva 23 6 QPS electronics – quench heater circuits III  Quench heater circuits - insertion region magnets and inner triplets –Quench heater power supplies installed in yellow racks underneath the magnets (Q7 to Q10) or in the corresponding underground area (Q4 to Q6, inner triplet, D1, D2, D3, D4) –Separated connections for coil instrumentation and heater circuits with connectors on both ends –Rupture of coil instrumentation connection with powered protection systems will cause discharge Insertion region magnet – heater circuit connection Insertion region magnet – instrumentation

7. AT-MEL-PM, R. Denz, CERN, CH-1211 Geneva 23 7 QPS electronics – quench heater circuits IV  Switching off of quench heater power supplies –Mandatory for access to IFS boxes, power supply itself … –Recommended in case people are working in the vicinity of the heater circuits –Classical “lock-out / tag-out” procedure can not be applied as power supplies cannot be padlocked –Once switched off an eventual trigger is inhibited and the power supply will discharge internally within ten minutes time –Capacitor bank voltage can be monitored by QPS supervision with power supply switched off Quench Heater Power Supply type DQHDS

8. AT-MEL-PM, R. Denz, CERN, CH-1211 Geneva 23 8 QPS electronics – quench detection electronics  QPS racks in LHC tunnel and underground areas –Yellow QPS racks underneath main dipoles –Protection rack type DYPG in underground areas –QPS current sensors type DQCSD for protection of corrector circuits –Detection electronics is on the same electrical potential as the superconducting circuit / magnet (up to ±1000 V DC to earth) ! –Only to be accessed by experts Also experts are supposed to follow the rules … Protection unit Q4.L8 & D2.L8 DQCSD type current sensors (picture courtesy HCC TWIKI)

9. AT-MEL-PM, R. Denz, CERN, CH-1211 Geneva 23 9 QPS electronics – QPS controls  QPS controls - expert mode –Expert commands are required for debugging, QPS-IST and specific hardware commissioning procedures –Remote activation of quench heaters and energy extraction systems Strictly reserved for QPS experts Not accessible to sequencer Not needed for LHC operation –QPS-IST will be only executed with permit granted by HC –During LHC hardware commissioning the QPS expert will only act on request by EIC QPS expert cannot check himself whether a given circuit is ready for a test  EIC’s responsibility (nobody is working on the corresponding DFB / magnet, ELQA finished etc.)