I have a problem about my DC Motor. DC Motor is 200Kw,1GH5 siemens.Field Coil was burned.I had doubt about over current.I installed Fuse in the circuit. Two months later, Field Coils was burned again. After Electrical workshop repaired ,I seperated field circuit from Simoreg Drive.Field Circuit was made from our electronic workshop.Nevertheless ,Over Voltage occur circuit in contrary to over current. This cause field coils burning. Why does over voltage occur. Sincerely

It is not clear from your post if you mean short over-voltages in the range of milliseconds or the over-voltages lasting hours. In my opinion, the short term over-voltages are irrelevant and cannot cause problems with the field winding. The long term over-voltages would be the problem of your power supplier. Just take into consideration that the field winding has to work successfully with voltages in certain tolerances, most of the time in +/- 10% range. If your voltages are in that range the problem is elsewhere.
The fusing of the field will probably not help. For example, if the rated current of the field is 3.1 Amps and you use 4 Amp fuse, the field current of 4 Amps will never burn the fuse but it will burn the field winding in very short time.
From my own experience, the burning of the field winding was in 99% of the cases due to lack of cooling.
Search this forum for other posts about field winding problem. The most recent is, I guess, the following:
http://maintenanceforums.com/eve/forums/a/tpc/f/7161085912/m/7381065633

jank

jank,
My field voltage is about 135VDC. I observed 270VDC in over voltage value.In addition, this value rise up.My Over voltage Relay cut off field circuit in few seconds.
There is not a problem in motor cooling.Regularly My personal check motor cooling.
I changed field cable and cable route so that electro magnetic field could be in the plant area.Nevertheless, this problem occured.

Hi erdal,
How do you supply the field voltage?
Why you separated the field circuit from Simoreg?

Cristian

Hi Christian,
I had suspician about Simoreg Field Circuit.Maybe,there could be a problem about diode, thyristor or circuit.
I supplied different 380VAC source. That is to say, simoreg and field supply are different. I observed field supply with Fluke 434 as over voltage occured.There wasn't anything change in supply voltage 380VAC.

I am not familiar with the Simoreg, but from the description it seems to be a constant current field supply. The best supply possible for the field circuit. The constant field current also means a constant flux density in the airgap of your motor. As the temperature of the field winding increases the voltage must also increase to keep the current constant. In this case it does not have too much sense to measure the field voltage; the field current is what counts. The current is always more important.
I would advise caution with your separate field supply. You may have solved one problem, but create several other potential problems. I can guarantee you that Siemens does know what they are doing.
I believe a prudent approach would be following the service manual of your drive/motor to the letter. It might as well be, that you are missing something that might bite you in the future.
jank

Hi jack,
My Line was built in 1990. We have used Simoreg 6RA24 Drive. There is not spare board.I talked Siemens Personel but they can't help.Thus ,I made field circuit.