The PS will soon be back in operation
The PS's power supply system is undergoing repairs for the accelerator to restart on 26 June.
The AB Department's Power Converter Group is working flat out with Siemens to return the PS's power supply system to working order. A problem appeared on the insulation of the power cables of the rotor of the rotating machine (photo) which supplies power to the PS magnets. To prevent more significant damage to the rotating machine, the AB Department, with the approval of the CERN Management, decided to shut down the PS which had started running on 15 May. Everything is being done to restart the accelerator on 26 June.
The PS's rotating machine comprises a motor coupled to a generator. The generator's rotor acts like a flywheel, supplying high-power pulses of 40 to 50 megawatts to the PS magnets. The 6 megawatt motor drives the installation at 1000 revolutions per minute and compensates only for variations in speed. It is an essential interface since it would be hard to imagine connecting such an electrical charge, pulsed every 1.2 seconds, directly to the electrical power grid. 'It really is the PS's pacemaker,' explains Frédérick Bordry, leader of the AB Department's Power Converter Group (AB/PO). 'The rotary unit completes five to ten million cycles per year and absorbs significant variations in torque during each of its cycles.'
The generator's rotor, which weighs 80 tonnes, was replaced in 1977 and operated without a problem for 27 years. In 2004, having identified signs of wear on the rotor's blades, the AB/PO Group decided to perform the necessary repairs before the start of LHC operations. The replacement rotor was thus installed in 2005 and successfully tested ahead of PS operations in 2006. The start of operations took place in February, without a problem. Unfortunately, on 15 May the teams that regularly perform routine inspections noticed pieces of insulation that had fallen to the ground and scratches on the stator. The decision was therefore taken to stop the rotating machine in order to prevent irreversible damage.
Siemens, which supplied the machine in 1968 and has carried out the maintenance work ever since, quickly sent a team to replace the faulty rotor with the one that has just been repaired. Several weeks'work will be required, given the difficulty of the handling operation and complexity of the electrical system. As a result, the AB Department is preparing to submit a new operating schedule which has as little impact as possible on users. The AB/PO Group is also examining solutions to replace this unique piece of machinery which will be celebrating its 40 years in service in 2008.
