We have 3 Alstom AC drives coupled together to a single motor (MV 3000 = MVDL 1000 x 3 Nos), now when the motor running at very slow speed (vector mode), it knocks and stops as if some mechanical gear locking and on one of the 3 drives coupled together one of the Phase U or W trips on a High current or on current imbalance. 4 Yrs this was running with out any problem.
Appreciate some one could respond on this subject from your experience.