Superconducting circuits: what remains to be done during hardware commissioning

1. Superconducting circuits: what remains to be done during hardware commissioning R. Denz AT-MEL-PM

2. Credits and Definitions • Credits • D. Bozzini (Electrical Quality Assurance) • K. Dahlerup-Petersen (Energy Extraction Systems) • Definitions • ELQA: Electrical Quality Assurance • QPS: Quench Protection System • EE: Energy Extraction System

3. Outline • The electrical quality assurance • Scope of ELQA • ELQA @ warm, during cool-down and @ cold prior to powering • The individual system tests of QPS and EE • Overview of the concerned systems • Surface tests • Tests during installation and prior to powering • Tests @ cold prior to powering • How will QPS and EE be qualified for operation? • QPS and EE during powering tests • Dedicated tests during the powering of the 1st sector • Resources in case of equipment failure • Conclusions

4. Electrical Quality Assurance - Scope • To electrically qualify each superconducting electrical circuit, including the current leads, at warm, during the cool down and at nominal operating conditions • To measure electrical parameters of each superconducting electrical circuit • To define reference values for the machine operation • Input parameters for power converters & digital quench detectors • To verify the integrity of instrumentation for the protection of the superconducting magnets, electrical circuits and current leads

5. Electrical Quality Assurance - Phases • ELQA surface activities prior to equipment installation • Line N cable segment • DFB’s • ELQA @ warm – test during assembly • Polarity, continuity & isolation • ELQA @ warm – test after closure of a sub-sector • Continuity and electrical insulation • Global resistance, inductance and global insulation • Verification of instrumentation • Concerns only instrumentation for protection • Only on DFB level and some connections to midpoints of circuits • Magnet instrumentation tested on magnet test benches ELQA activities require QPS equipment being disconnected from the DFB’s (to be re-connected after the last insulation check @ cold)

6. Electrical Quality Assurance - Phases • ELQA during cool-down • 50V automatic insulation test • Magnet instrumentation monitored by QPS • ELQA @ cold • Continuity and electrical insulation • Global resistance, inductance and global insulation • Estimated time for tests @ cold = 3 weeks / sector • Last test prior to powering • QPS equipment will be definitively connected after this step (< 1 week /sector) Insulation tests may imply certain access restrictions.

7. QPS & EE systems - overview • Dedicated protection systems for all circuits with INOM ³ 600 A • Main dipoles and quads • Cold by-pass diodes & analog quench detectors & quench heater power supplies & energy extraction systems • Main busbars • Digital quench detector with distributed voltage pick-ups • HTS current leads • Individual protection by digital protection system • Insertion region magnets and busbars • Global protection of magnet and busbar by digital quench detector + quench heater power supplies • Correctors and busbars • Global protection of magnet and busbar by digital quench detector & energy extraction systems (if required) • Protection of 60 A and 120 A circuits by corresponding power converter

8. Individual system tests of the QPS • Verification of the correct installation of all quench protection equipment with respect to the corresponding implementation plans. • Commissioning of the QPS supervision system. • Functional test of all quench detectors. • Test of the QPS quench loops, which are internal to this system. • Functional test of all quench heater circuits.

9. Individual system tests of the QPS prior to installation • 100% functional test of each individual system prior to installation in the LHC tunnel • Programming of the equipment according to its functional position in the LHC • Integration of the test and equipment data into MTF • Exhaustive test of the equipment supervision • Final verification of detection thresholds, quench heater powering etc. • Electrical isolation tests • Tests performed in collaboration with BARC / India Dipole protection rack on QPS test bench in building 287. 1st test campaign currently starting up. Expected rate 8 to 12 main magnet protection racks per day – other systems according to requirements.

10. Individual system tests of the QPS during installation and prior to powering • Partial powering of the QPS equipment after installation • Equipment not connected to superconducting elements but to interlocks and fieldbus connections • Quench heater power supplies are switched off • Detection inputs are shorted • Verification of the fieldbus connection • Address, equipment name & functional position • 1st sector will be the 1st opportunity to test QPS supervision under realistic conditions and with the full data load • Pre-commissioning of some special equipment • Protection systems for 13 kA main busbars • Quench loop controllers

11. Individual system tests of the QPS @ cold prior to powering • Test of the quench heater circuits & quench detectors • Test of the quench detector • Artificial test signal generated by quench detection hardware • Discharge of quench heater power supplies (if applicable) • Automatic test procedure for the main circuits • Individual trigger for insertion region magnets and inner triplets • Mandatory to verify the proper functioning of the quench heater power supply and the quench heater strips • Analysis based on the content of post mortem buffers • Tests to be repeated on a monthly basis during LHC operation • Test activates the interlock loops and can be combined with the respective tests Once quench heater power supplies are charged access to the concerned QPS equipment and the respective connection boxes on the magnet or DFB side is forbidden.

12. Individual system test of EE systems • For the 32 systems of 13 kA circuits: • To check that the basic electrical, mechanical and hydraulic parameters of each system have not changed since the ‘Global System Tests’ were performed at IHEP (Russia) prior to delivery and installation in the LHC. • At the stage of the ‘Global System Tests’ the electrical data originate from measurements in short circuit (i.e. no stored energy available) • To commission the cooling stations for the extraction resistors. • For the 202 systems of 600 A circuits • To confirm all functional aspects and results of system tests performed at the surface prior to their installation.

13. Individual system test of EE systems continued • For both 13 kA and 600 A facilities: • To verify the local infrastructure, required for operating the EE facilities, once connections to the equipment are established. This concerns mains, UPS, controls infrastructure, the QPS quench loop for power abort, the discharge loop, the SOF (switch-opening-failure) detection loop and cooling water. • To perform functional tests of the complete facility. • To commission the supervision system of each facility. • To check the timing and sequence of interlock signals. • Verification of noise immunity. • Verification of behaviour during failure scenarios. • To verify the adequate activation of the internal fault signals.

14. Individual system tests of the EE systems during installation and prior to powering • Conduction of complete-system functional tests • Functional checking comprises all operational aspects, including failure modes, as well as a verification of the control, monitoring and data acquisition systems in both ‘local’ and ‘remote’ modes • Tests of the individual sub-systems • Extraction switch assembly, extraction resistors & bus-ways • Electrical, mechanical and hydraulic performance monitoring • Voltage withstand test and insulation resistance measurement • Closing / opening cycles • Simulation of fault conditions and verification of interlocks • Accidental, controlled opening, switch-opening-failure, mains (UPS) failure, cables removal, spurious opening of a switch, capacitor discharge, power supply failure, over-current detection, closing failure etc. Thermal evaluation will take place during the short-circuit tests of the power converters.

15. How will the QPS and EE be qualified for operation? • Individual system tests essential but not sufficient for full qualification of QPS and EE • QPS & EE must be fully operational prior to beam commissioning • Qualification of safety systems does not allow shortcuts • Defined sequence of specific tests for QPS and EE in accordance with LHC-D-HCP-0003 • Tests @ stand-by current and @ injection current • Tests @ 30%, 66% and 80% of nominal current • Tests @ nominal current, first with one then with all circuits of a sector • Conditions • ELQA and individual system tests successfully terminated • Controls infrastructure available • Logging, timing, alarms & post mortem • Field Control Room, UPS powering, cooling & ventilation etc. available

16. Interlock tests @ stand-by current • Hardwired interlock loops for the Power Abort signal • Current loops linking the power converter, the powering interlock controller and the quench protection system • Long current loops internal to the quench protection system for the main circuits (linking the odd and even points) • Software link for the transmission of the Power Permit signal LHC-D-ES-0003 rev 1.1 Current loop internal to QPS linking the odd and even point of an arc.

17. Interlock tests @ stand-by current - continued • STRING II experience – switching from zero to stand-by current sometimes not so easy • Faulty instrumentation wires • Wrong circuit parameters loaded (e.g.: for digital quench detectors) • EMC problems Digital protection unit DQGPU for the protection of 4 corrector circuits. • Interface tests between the different systems absolutely mandatory • Quench detector & power converter connected to the same circuit? • Abort signal properly received and treated by PIC? • Power Permit signal correctly generated and routed? • Discharge requests by EE and power converters seen by QPS?

18. Power tests @ injection current • Energy extraction discharge (only where applicable) • One discharge per EE system before provoking any quench • Quench detectors • Stability & noise immunity to be verified • Quench heater firing • All quench heaters in case of insertion region magnets • Selected magnets in case of main circuits • Selected heater firing (see slide 20) to be tested during commissioning of the 1st sector • Simulation of a fault of the main circuit EE systems

19. Power tests – current profiles • Problem: detection of “bad” splices during 1st powering of a superconducting circuit • Quenches in “bad” splices develop slowly and may me detected too late (i.e. beyond damage level) if ramping with nominal parameters • Remedy: • Stepwise ramping to nominal current with intermediate evaluation • Semi-automatic procedures for correctors and insertion region magnets (currently under discussion) • Manual evaluation for main circuits (few circuits, higher risk) Procedure only required for the 1st powering of a superconducting circuit and after thermal cycles and interventions (T>80 K)

20. Power tests form intermediate current levels to nominal • Tests foreseen for all circuits with magnets equipped with quench heaters and / or energy extraction facilities (including those with a 50 mW discharge resistor internal to the power converters) • Energy extraction discharge • Quench heater firing • Verification of quench heater performance • Only one magnet per main circuit • Energy extraction discharge @ 80% of nominal current for main circuits • Nominal • Energy extraction discharge • Quench heater firing (one magnet per circuit) • Nominal with all circuits in unison • Surprises not excluded • Final qualification after 24 hour run Quench tests also required for validation of cryogenic recovery procedures. During the 1st ramping of a superconducting circuit the HTS current leads have to be commissioned at the same time (proper setting of cooling & heating …)

21. Dedicated tests during the powering of the 1st sector • Validation of digital quench detector firmware • Adjustment of digital filters and inductance tables • Commissioning of automatic test procedures • Preparation of automatic powering procedures and battery tests • Test of selected heater firing @ injection current • Selected heater firing is the only way to prevent equipment damage to the main circuits in case of a failure of the 13 kA energy extraction systems • Functionality tested without current during QPS and EE individual system tests (for every sector) • Tests @ injection current will quench magnets but limit the amount of dissipated energy • Test foreseen with one dipole EE system and one quadrupole system • EMC tests in collaboration with AB-CO and AB-PO

22. Estimated resources in case of equipment failure • ELQA resources are limited and calculated for the best case • In case of non-conformities diagnostics may have to be scheduled according to the available resources • ELQA and QPS can reveal non-conformities inside the cold masses and on the connection side level – but they have no mandate nor resources to fix these problems • QPS equipment failures • Typical intervention time ³ 1 hour • Time may significantly be reduced during the hardware commissioning in case of • Field Control Room • Spares stored in or close to the concerned area • QPS programming tools available in the field

23. Conclusions • Proper Electrical Quality Assurance essential for LHC operation • Non-conformities in the superconducting circuits not revealed by ELQA may cause long intervention times afterwards • QPS and EE must be fully operational prior to beam commissioning • Test must ensure 100% functionality • Shortcuts during test & commissioning not acceptable • More time required for the hardware commissioning of the first sector in order to ensure smooth commissioning of the others • Required time will not only depend on the respective hardware commissioning procedures but as well on the number and kind of non-conformities revealed during these exercises • No contingency to deal with non-conformities not related to QPS & EE equipment