Rotor Lock (VSD-Cegelec)

Hye All,

i encounter a new problem with my VSD motor. Really appreaciate if you guys can give me some idea to troubleshoot this problem. the cronology as below:

We shutdown the motor (29/07/2008 @ 1100) due to sound abnormal. the operation suspect the sound coming from the bearing. once the mechanical settled inspected the bearing, operation request to run the motor(solo run). unfortunately, when the motor start, the RPM start to increase. so thus the current. its normal for the current to increase since it was starting current. but then when to motor reached 50rpm, then it starts to reduce the rpm but the current continue increase until the motor trip. when obserse at site, once the motor tripped the shaft (with coupling hub) stop immediately like something hold the rotor.i did check the exciter bridge, machine bridge and also network bridge, but everything in good condition. from the mechanical opinion the bearing still ok since the shaft can be manually rotate. below are the detail of the motor:

rated current 800A

rated voltage 2.2kV

exciter rated voltage 415V

during the problem the exciter current show at 240A.

really need your help. if need more information please let me know.