We have 3 Alstom AC drives coupled together to a single motor (MV 3000 = MVDL 1000 x 3 Nos) on our ship, 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. For testing purposes When we diconnet all drive output and run one one at slow rpm it does not lock but cannot incresae speed as motor is 2800 kw. Connect two or 3 drives together then again it starts knocking and braking & trips.
Appreciate some one could respond on this subject from your vast experience.
Have you checked the tuning of the drive to the motor?
This is very important in vector mode.
Some drives refer to this as an ID run.
The system was working for 4 yrs and it has a controller common for all 3 drives together so did'nt bother to check the tuning. I just took the scope readings of all 3 phases of all 3 drives after disconnecting all cables to the motor (2880 KW) and two drives the pattern on U phase and W phase found different -- like firing only negative cycle or positive cycle where as the V phases all looks same -- but cannot trust scope due to harmonics---When checked with Alstom, they advise me to change all drives and delivery tome is 20 to 26 week so trying all my best as in Alstom UK has also all new young lads..