Download Electrical safety of LHC quench heater circuits in case of

Electrical safety of LHC quench heater circuits in case of
faulty heaters by
 Motivation
– So far quench heater power supplies have to be switched off prior to
work on the corresponding DFB for reasons of electrical safety
• No problem for insertion region magnets (up to 12 power supplies
per DFB)
• Significant amount of work for the main circuits (up to 718 power
supplies per arc)
 Risk of an electrical shock hazard caused by the quench heaters is
extremely unlikely under normal operating conditions
AT-MEI-PE, RD, MPP 16-JAN-2008
– People follow the rules …
– Installations are conform (i.e. quench heaters are isolated from the cold
mass and the coils)
 Electrical shock hazard may be possible in case of
– Vandalism and other severe professional faults …
– Earth fault of quench heater circuit & (spurious) trigger of quench
detection system  to be checked
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Experimental setup
 Proposal by Hugues: experimental verification of “worst case scenario”
– Measure voltage developed by fault current in case of discharge into a heater
exhibiting an earth fault
AT-MEI-PE, RD, MPP 16-JAN-2008
– Determine the possible risk for a human connected in parallel (e.g. leaning
across a DFB)
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Results & conclusions
 As expected fuse blows and protects the equipment
 Maximum observed voltage: U_max = 22 V, t < 0.1 ms
 Tested configuration represents no risk for electrical shock hazard
– is it really the worst configuration?
 QPS prefers nevertheless that the current leads will be connected prior to
charging the quench heater power supplies
AT-MEI-PE, RD, MPP 16-JAN-2008
– ELQA has to be finished as well (possible source of spurious triggers)
 All current leads must be shorted and properly earthed before work on the
DFB can start (in case quench heater power supplies are charged)
– Proper earth connection requires low resistance and inductance
 For all circuits other than RB, RQD and RQF the quench heater power
supplies will be switched off in case work on the DFB is necessary
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