480V to 480V Isolation transformer question.

[Gary Gagnon]

Hey guys. I have a need to isolate a production cell from the rest of the plant. Its fed from a standard 60 amp buss switch down through a 60 amp disconnect, with 40 amp fuses directly to servos, then a single phase 5kva transformer for 120 volts that runs all the PLC, pneumatics, conveyor motors, ect... We have experienced a few isolated issues where the servos (AB Kinetix) have picked up stray high voltage (brownouts/spikes?) from the plant and I'm wanting to put this machine on its own transformer, or figure out some protection.
I know the machine draws around 12'ish amps while running. I have 3 questions:
1.) should I reduce the disconnect fuse size and run a smaller ISO transformer (9 & 10 KVA seem to be common sizes)
2.) what type of isolation transformer should I purchase? I've never spec'd one before. They seem to be mostly delta/wye, but I'm not sure if I want or need 3ph neutral. Delta/Delta xfomers seem kind of rare in smaller applications like mine.
3.) is there a better way to protect our expensive servo machines, other than an isolating xformer on the 480, for reasonable money?

 

[jim dungar]

If you want to go the route of a transformer instead of a filter, look into 'drive isolation' styles. Every major manufacturer offers them

 

[Gary Gagnon]

Its not that I have a preference, my experience (induction melting) is that isolation transformers are good for blocking transients from passing through. If a filter does an effective job, i'm ok with that too. From what I've read, drive isolation is basically moving the isolation transformer from the whole machine, to just feeding the 480 to the servo drives. Thats a good idea. I could probably get away with a 5 or 7.5 KVA. I'll get some amperage data and size that out. Should we then attach the secondary delta neutral to chassis ground?

 

[jim dungar]

Its not that I have a preference, my experience (induction melting) is that isolation transformers are good for blocking transients from passing through. If a filter does an effective job, i'm ok with that too. From what I've read, drive isolation is basically moving the isolation transformer from the whole machine, to just feeding the 480 to the servo drives. Thats a good idea. I could probably get away with a 5 or 7.5 KVA. I'll get some amperage data and size that out. Should we then attach the secondary delta neutral to chassis ground?

You would not have a secondary delta with a neutral. You will have a secondary wye or a delta. My guess is your servos need to have a reference to ground, so a wye with a grounded neutral is probably the best choice.