NEMA A vs NEMA B 1

[smeg]

I have recently stumbled into a problem. I admit that I am no expert on NEMA and or motors, I can control and write the code for one so long as it runs. Here is the prob. I have a 200HP Motor with a 250HP afd on it. The load an be erratic and in the past I have used a dynamic resistor to absorb regen. Through no fault of my own we have wound up with a NEMA A motor on it (I read some of your comments about getting a cost reduction - exactly that!!) Anyway, as the motor reaches synchronous speed, the drive faults out on locked rotor current. The current tries to go through the roof. If I run at a reduced speed say 90% of sync speed, it runs fine. Only when I run towards 60HZ this happens. Can anybody help me understand why? Is this symptomatic of NEMA A? Should I be able to tweek the AFD into not being so clever and adjust characterisics to overcome this or am I screwed until I get a NEMA B on there?
Any help will be gladly received
Thanx

 

[smeg]

Thanx, I am witing to hear the rsults of the test with droop (typo DickDV) and disabling the Vector. The more I go into it and hear your comments, the more I believe there is an answer here. Thanx again for all your assistance.

 

[smeg]

Kind of anti-climax I guess. I could not contact the site engineer to check the suggestions, but he did contact AB. They came they fitted an "impact board" and everyone went home happy. So there remains a slight haze over what would have worked. I still maintain there was a fix somehow with the 1336 but at least there is no bread shoratgae this week.
Thanx to all who helped.