Facility converting service from 120/240V 3ph, 4W delta to 277/480V Wye

[housemoney]

Facility with lots of small motor loads, some existing motors & lighting staying, new service and distribution equipment going in.

Other than the obvious- existing equipment ratings, breaker ratings, available fault current etc. what are some other items to watch out for when changing service voltage?

 

[hillbilly1]

I did the exact thing to a paper recycling plant about 25 years ago. Just added a 75 kva transformer to feed the old existing service, all of the new stuff they added came off the 480 volt service. Had a battle with the inspector though, couldn’t get it through his head I had to use yellow brown purple for the new service because the old service had to be black orange blue because of the high leg.

 

[augie47]

Keep in mind the old service was 240. Because of the restriction on neutral loading the transformer(s) you add for for 120v loads will likely be 208/120. There may be some equipment that actually requires 240 an you will need to address that.
Like hillbilly, I have converted a few plants. On a couple of them we added a 208Y/120 and a 240/120 (4w) transformer.

 

[winnie]

I think augie47's point is important. You are going to need a 480V to 2xxV transformer, and _most_ 480V to 240V high leg delta transformers have a restriction on neutral loading.

If your system can tolerate 208V, then 120/208V is preferable for your 2xxV system; but if you really need 240V then you need to think about the neutral loading issue. There is no physics requirement for the neutral current limit; simply a transformer design issue, so your choices as to the approach here.

Depending upon the upgrade you might also end up with higher available fault current issues.

-Jon

 

[petersonra]

It seems likely to me that all your 240 V single phase and 120 V loads are on the same panelboard(s). Maybe you could just add a single phase 480 to 240/120 V transformer for those panelboard(s).

 

[don_resqcapt19]

I think augie47's point is important. You are going to need a 480V to 2xxV transformer, and _most_ 480V to 240V high leg delta transformers have a restriction on neutral loading.

If your system can tolerate 208V, then 120/208V is preferable for your 2xxV system; but if you really need 240V then you need to think about the neutral loading issue. There is no physics requirement for the neutral current limit; simply a transformer design issue, so your choices as to the approach here.

Depending upon the upgrade you might also end up with higher available fault current issues.

-Jon

The answer to that is to build the bank with 2 or 3 single phase transformers in place of using a 3 phase transformer. That way the transformer that is center tapped for the line to neutral loads can be sized larger to support the single phase line to neutral loads.

 

[d0nut]

It may also be more beneficial to swap out any 240V only loads you have with equipment that can operate at 208V, depending on how many, what size, and how old those loads are. You may also end up with separate 208Y/120V systems and 240V 3 phase, 3 or 4 wire systems. It may be worth spending a little more money now to simplify the distribution for the facility going forward.