I'm hooking up an abb robot which requires 475v 3ph 7.2 kva. The shop has 208 3ph and my electricians are suggesting wiring a step down transformer backwards. But I'm concerned that if it's not a buck/boost that any fluctuation will damage the robot. I'm also ignorant about what the kva rating on the transformer should be. For some reason I've had a hard time finding people with transformer expertise to help me understand the equipment I need. Any help is greatly appreciated. I would post a picture of the tag but I can't figure out how to do that here.
Stepping up 208-460 3ph for robot
- Thread starter kceegee
- Start date
- Location
- Illinois
- Occupation
- retired electrician
I approved this based on the statement that electricians working for this general contractor will be doing the work, and this post is just asking for advice.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Just buy the correct Delta/Wye step up transformer. A reverse wired standard transformer will have Delta secondary which will be ungrounded unless you want to use a corner grounded system. I'm guessing that you don't want that.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Note that transformer used in reverse will often be a delta on the 480 side in this case, so you would will either corner ground it or leave it ungrounded and install ground detectors. Neither is really a big deal, but more importantly, the machine may need a grounded wye supply. I would confirm with the manufacturer it's ok if you go that route.
Probably a 10kva transformer would work.
Edit: and I agree with infinity, the correct transformer would be best.
Probably a 10kva transformer would work.
Edit: and I agree with infinity, the correct transformer would be best.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
The robot supplier should be able to supply the transformer. I have a customer that has a lot of Italian and German machines, and I just make sure the manufacturer sends the transformer with the machine. Usually they are an auto transformer with multi taps for anything from 208 to 480.
winnie
Senior Member
- Location
- Springfield, MA, USA
- Occupation
- Electric motor research
I concur with the above. You do not want a reverse fed 480:208V transformer. You want a proper 208V delta to 480/277V wye transformer, or a wye autotransformer.
9kVA is a standard size which should do fine unless there are large startup loads.
9kVA is a standard size which should do fine unless there are large startup loads.
electrofelon
Senior Member
- Location
- Cherry Valley NY, Seattle, WA
Guess I was thinking of single phase where 10 is a standard size. I don't think I ever noticed 9 was a standard size for 3 phase
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Transformers can be built in two different styles: Isolation and Autotransformer.
In the US, Isolation is the most common style, installed by contractors for power distribution, while Autotransformers are not uncommon for dedicated loads. In American most autotransformers are field assembled into bucks boost configurations for voltage changes in the 10-20% range. Many foreign machine makers will supply auto transformers in their machines with voltage ranges in the 125-200% range.
Your bigger concern should be the load side winding configuration of Wye or Delta. Wye systems are probably the most common configuration in the world, excluding residential. Most surge protection systems are designed for the line to ground voltages found with Wye systems. While not rare, delta connected transformer outputs are not common. Many electricians are not experienced with installing or troubleshooting ungrounded or corners grounded delta systems which have 'special' NEC installation considerations.
In the US, Isolation is the most common style, installed by contractors for power distribution, while Autotransformers are not uncommon for dedicated loads. In American most autotransformers are field assembled into bucks boost configurations for voltage changes in the 10-20% range. Many foreign machine makers will supply auto transformers in their machines with voltage ranges in the 125-200% range.
Your bigger concern should be the load side winding configuration of Wye or Delta. Wye systems are probably the most common configuration in the world, excluding residential. Most surge protection systems are designed for the line to ground voltages found with Wye systems. While not rare, delta connected transformer outputs are not common. Many electricians are not experienced with installing or troubleshooting ungrounded or corners grounded delta systems which have 'special' NEC installation considerations.