failed drives

[Besoeker]

Yes, that's how YOU do it, because you know what you are doing.

We do it because we have to. It's quite expensive to have an AC3 rated contactor.

Thanks for the kind words. And apologies for truncating your post.

 

[graywolf]

Other duties prevented further investigations today, but i am thankful for all help:roll:

 

[Besoeker]

Other duties prevented further investigations today, but i am thankful for all help:roll:

Wait til you git the bills in.............
But will lycanthrope pay them?

 

[graywolf]

problem solved

problem solved

Thanks to all , turns out rockwell used bad resisters in this model drive.
they are replacing all defective resistors.

 

[Besoeker]

So assuming you are comfortable with the cooling system, and the application is correct (per kwired's response), power quality is a likely candidate, especially if the caps are involved. On the large drives like that, the big caps have what are called "balancing resistors" across them, which help to even out the stresses the caps see from grid transients that come right through the bridge rectifier. Years of severe transients will take out those resistors, which is followed shortly thereafter by cap failure, followed shortly thereafter by transistor failure. Regular preventative maintenance programs will include inspection and periodic replacement of those balancing resistors. Ignoring PM on drives leaves those resistors (and other things) as ticking time bombs.

I respectfully disagree.

We have been making variable speed drives from component level for about forty years. Mostly custom built. I was on site yesterday looking at two we built in 1993. The DC link is 1170Vdc. The bucket capacitors, 192 in total in each drive, are arranged in strings with four caps in series. Each capacitor has a 22kohm resistor in parallel with it.

The purpose of the resistors is twofold. The first is to ensure that the capacitors will discharge within a reasonable period on removal of power.

The second is to ensure voltage balance across the series banks in operation. Actually, on this project, we have voltage monitoring on the capacitors that goes into the PLC and is displayed as one of the trends on the SCADA system. If over voltage is detected on any of the strings it shuts the drive down.

Mains borne transients will not significantly change the voltage. These have vastly greater energy storage capacity than any transient voltage surge suppressors.

Of course, if the resistors fail on any string that will affect the balance and, if not monitored/detected that can lead to over voltage and the subsequent destruction of capacitors.