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User name stevens
Log entry time 09:09:36 on July 8,2000
Entry number 45355
keyword=Hadron dipole failure
During the recovery from the refrigerator casualty, the hadron dipole wouldn't restart. We found two phases of power reading low (100-200VAC). Investigation revealed that the phase power detector which turns on the red strobe "MAGNETS ON" lights short-circuited and burned out the three phase 480VAC fuses in the UPS BYPASS switch box. Aparently the 3 phase UPS back-fed 1 phase 480VAC and low voltage on two more phases. The back fed power caused no harm, and posed no personnel hazard because normal procedures to isolate power also isolated the backfed power. But it did create a rather bizarre failure mode in which the power supply partially lights up and seems to be on, but it does not respond to control input, and it reads back current output (about 300 amps) that does not exist. We replaced the burned out fuses, removed the bad phase detector, put the strobe lights on manual operation, and restored power. The dipole power supply responded normally. We will investigate the back-fed power problem during the next maintenance period.