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    User name stevensm

    Log entry time 14:39:14 on October18,2005

    Entry number 157303

    This entry is a followup to: 156968

    Followups:

    keyword=tech/right dipole disengaged

    On Monday we began trobleshooting the right dipole problem, which seemed to be primarily the fact that the M3 (main output) contactor never closed. Coincidentally, we were seeing FC (thyristor fire control) fault and sometimes a ZFCT fault, but these usually cleared normally, and are unrelated to the main problem.

    Viewing the dipole gui, the failure mode appears as a normal start sequence, but although the power supply status changes from "off" to "on", the magnet status remains disengaged, and a "power supply" fault appears. The power supply fault can be cleared with a reset, but the magnet cannot be ramped. The M3 contactor status bit appears in the gui as the "Magnet" status (disengaged = off, engaged = on).

    Locally at the power supply, the failure mode appears as a normal start sequence, but the M3 lamp never lights, and the sound that M3 makes is changed from the normal "zzzzzClunk" of the motorized circuit breaker closing, to a louder zzzzzCLACK" of the motorized circuit breaker tripping on closure. And we found that when we took the front cover off of M3, it would not "cock" when the handle was moved to the off position, even if the undervoltage release was manually held engaged.

    We found that the Undervoltage Release device in M3 was receiving 110VAC just like it should (the undervoltage release is part of the protection system). The undervoltage release is the only installed trip device in M3. The device's mechanical linkage immediately became suspect. We changed the undervoltage release coil, and the entire breaker with no joy. Eventually we learned that the cam and pawl device that is part of the undervoltage release had a bent pawl, which is made of spring steel. The bend resulted in the mechanism not pushing the solenoid up far enough to be held by the 110 coil, and thus the switch was in a continuously "tripped" state. We replaced the cam and pawl device, and it worked normally.