DC Motor flashover
DC Motor flashover
(OP)
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 volts of the group via a single quadrant thyristor converter. The Centre roll motor's armature is connected across this armature voltage and we control the load on this motor by adjusting the field current, the back emf then controls its armature current. The motor will be working fine, no sparking, steady current, steady speed, and then suddenly flashover between brush arms. As well as flash damage, the interpole windings get distorted, which causes us a lot of down time. The spare is fitted, and this can then work fine for months and then out of the blue, bang, another flashover. The other motor in the group, a 290kW never suffers this problem although its control is the same. We suspect the problem maybe caused if the field controller goes faulty and we get an increase in field current turning the motor into a generator and getting the flashover. We have changed field controllers but still had the problem! Has anyone got any idea's





RE: DC Motor flashover
RE: DC Motor flashover
After 20 years, you might consider a total rewire.
RE: DC Motor flashover
A rebuild is easier and lower cost than you may think. I am doing that on a Jagenberg right now and the material costs no more than around USD 5000 for each drive. You keep the DC motors and get modern digital four-quadrant rectifiers. You can do the rebuild in steps. Changing the problem drive first. And possibly stay there.
Your next flash-over and subsequent production loss will probably cost more than the rebuild.
Gunnar Englund
www.gke.org
RE: DC Motor flashover
RE: DC Motor flashover
So thanks once again for your thoughts
RE: DC Motor flashover
My answer to students question,
"What's the difference between a D.C. Generator or a D.C. motor?"
Answer
"Often only a few volts or a few RPM."
We would then set up the equipment in the shop and verify the statement.
RE: DC Motor flashover