Report on problem in opening the 13kA EE system (issue recently found during last CSCM) Bozhidar Panev

FPA Loop topology reminder Problem with “opening” of the 13kA EE system Finding the origin Fixing the issue Test result and performance validation Outline

RB FPA loop - before and after LS1 Before LS1 After LS1 The new introduced voltage dividers into FPA loop determine a total leakage of ~1mA The FPA loop can be ruptured by all quench detectors + SUMFLT of EE systems

On 14–Aug–2014 as a part of CSCM preparation, the quench was simulated from nQPS unit B12L1. The dipole EE system in UA87 did not open its switches – ABNORMAL! The leakage current measured by DQQLC_EVEN was: I_LOOP = 1mA. The investigation began focusing on the FPA board in the EE system. 13kA Dipole EE system in UA87 did not react The FPA board is meant to sense the FPA loop current and to issue an opening command when the quench loop is ruptured. It has two independent sensing channel based on optocouplers. Optocouplers

Simulation of one sensing channel in FPA board A current of 1mA was simulated to flow through the primary side of the optocoupler in order to check whether it is enough to keep the EE system “blind”. Result from the simulation: The switches will remain closed at I_LOOP = 1mA. The relay is not powered  No opening command.

Measurement of the I_LOOP and FPA_REC1&2 In order to find at what I_LOOP value the optocouplers react (EE system opens switches), a measurement was set on test stand in bld.377 Three spare FPA boards were measured and they gave very similar results – the reaction of the EE system occurred at I_LOOP = (120÷150)uA. The conclusion: From the simulation and measurement results it became clear that at 1mA leakage current the switches remain closed. To avoid that, an urgent modification on the FPA board was required. (120÷150)uA. Current

Modification of the FPA board The easiest solution: Add the resistor in parallel to the primary side of the optocoupler. It was calculated that R=100Ω  The threshold of the optocoupler is lifted up to 10mA. The advantage: The modification does not interfere the secondary part – the RC delay stays as it was before. The relay is powered  Switches open

Measurement of the modified board in bld.377 The modification was implemented in one spare FAP board and the measurement was carried out to prove the simulation. The reaction of the EE system occurred at: – I_LOOP = 9.8mA  FPA_REC1 – I_LOOP = 9.6mA  FPA_REC2 Current

After re-installation of the modified boards in RR13 and UA87, the quench was simulated from a few different locations in the sector including (A8,B12)L1. – At 15:54h on quench was simulated from DQLPU A8L1: PM files: _ _A8L _ _RR13.RB.A81  delay = 346ms _ _UA87.RB.A81  delay = 580ms I_LOOP measured by DQQLC_EVEN = 1mA. Conclusion: Correct performance was observed form the RB EE systems Performance verification of the modified FPA boards in sector 8-1 (RB EE systems)

After modification all boards were tested in the test stand in bld.377 prior to be re-installed back in the tunnel. Currently all 13kA EE systems in LHC except one in RR57 are already equipped with the modified FPA boards. As soon as the cooling process in sector 56 is over, the last board will be also fixed. Test results from the modified FPA boards RB.A81 UA87  10.2mA RB.A81 RR13  10.35mA RQD.A81 UA87  9.8mA RQF.A81 UA87  9.7mA RB.A12 UA23  9.6mA RB.A12 RR17  10.1mA RQD.A12 UA23  10.35mA RQD.A12 UA23  10.3mA. RR57  TO BE DONE Some test results from bld.377 Adding 100Ω resistors

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