Hi all 

    we are using 6ra7015 to supply  a DC generator field to control the generator , the generator voltage is controlling the speed of 2 dc motors connected in series , the motors field is connected in series too through a separate supply . the application is crane slewing system . the problem is that when we run the motors the go over speed and with high current that the generator trip , i checked every part of the system and found nothing faulty . as we are in urgent situation and to over come my problem i had reduced the output voltage of the drive to the generator field to the minimum value i can also i change the speed reference to about 2 % . this way the motors current is about 98% . wish one can help investigate the problem and how to solve . motors field current were measured and found ok , there is no generator voltage  feedback  connected to the drive ,only tacho and motor aramature current , insulation , brushes and commutator found ok . the problem exist even the motors are decoupled from the gearboxes . attached the  dnl file