Thanks for all the replies. It looks as though the motor field variation is the most likely cause. We do have a field failure relay in the circuit, and it has never operated, and we also have changed the field failure relay in case it was faulty. We put some monitoring equipment on, and at the...
We recently have had 3 flashovers over a period of about 2 years on a 330kW 750volt DC motor on a Centre roll drive on a paper machine, that has been in service for about 20 years. The Centre roll is in a group of 3 drives, one of which is a master drive with an encoder controlling the armature...
