Burning Of Fuses Of A Dc Drive 95Kw

[AB2005]

Hi;

Please see the attached image which is a diagram of power circuit of a 95KW DC drive. There are two fuses mentioned for each phase and each fuse is 660V 200A rated. Am I correct that one fuse of each phase is for forward operation and second fuse is for reverse operation? Please make me correct if mistaking.

This drive (almost 20years old) runs a 93.6KW motor of a single facer unit of Corrugator machine. We have been facing a problem with this drive that some time (after one or two months) its fuses blow out. Some time three fuses some time four and some time five. There is no any jamming in machine which leads to blow out the fuse. We have made test of motor and found it ok. Matter of thinking is that why fourth or fifth fuses are blown.

[mariomaggi]

Dear AB2005,

I guess that this drive could have some problems due to age of the control card. Are there some electrolytic capacitors that now are no more efficient? You can look also to disturbances coming from cables or radio, probably such disturbances increased during years. I don't see in your diagram any inductor, I hope that it is connected is series to your DC motor.

Best regards,

Mario

[marke]

Hello AB2005

 

No, the fuses are not for forward and reverse.

You have one fuse for current from phase 1 to the positive terminal and 1 for current from phase one to the negative terminal.

In forwards, positive current will flow to the positive terminal and negative current to the negative terminal.

In reverse, Negative current flows from phase 1 to the positive terminal and positive current flows from phase 1 to the negative terminal.

 

Fuse failure can be due to commutator and/or brush problems in the motor. Fuse failure can also be due to triggering problems with the SCRs.

 

With the reversing drives, only half the SCRs are used forwards, and half are used reverse. If some of the unused SCRs are accidently triggered on, you will effectively short circuit the supply and a fuse or two will fail.

 

I would check all the wring and connectors between the SCRs and the motor. I would also carefully check the snubber networks, if the snubbers are not working, the SCRs can be turned on by dv/dt.

 

I would also thoroughly check the control board for faults.

As Mario suggests, check all the electrolytic capacitors in the unit.

 

Best regards,

Mark.