• F. Formenti, Z. Charifoulline, G.-J. Coelingh, K. Dahlerup-Petersen, R. Denz, A. Honma, E. Ravaioli, R. Schmidt, A.P. Siemko, J. Steckert
  CERN, Geneva
• SF. Feher, R.H. Flora, H. Pfeffer
  Fermilab, Batavia

Two events, occurring in 2008 during commissioning of the LHC circuits, lead to fundamental changes to the scope of circuit protection. The discovery of aperture-symmetric quenches and the accidental rupture at 9kA of an interconnecting busbar resulted in an emergency program for development and implementation of new protection facilities. The new scheme comprises a distributed busbar supervision system with early warning capabilities based on high-precision splice resistance measurements and system interlocks for rapid de-excitation of the circuit in case of a sudden splice resistance increase. The developed symmetric quench detectors are digital systems with radiation-resistant FPGA logic controllers, having magnet heater firing capabilities. This program successfully allowed a safe re-powering of the collider. The concept of the new electronics boards and the powering modules will be described. More than 14'600 extra cables and 6'000 new detector and control cards were added to the existing QPS system. A first evaluation of the system performance as well as a number of interesting discoveries made during the commissioning will be presented.