240V delta

[jeff motta]

I am looking for some advice, I have a client who wants to add a power panel for 120v receptacles around the plant, I found a spare 200A 3phase breaker available, but the service is 240V delta. I plan to come off the spare 200a breaker from the 240v delta panel, install a 75KVA 240 delta to 208v/120v wye transformer to feed the new power panel, I wanted to know if there are any specifics as to breaker/fuse sizing.

Thanks

 

[augie47]

Art 450 for transformer protection (normally 125%) then Art 240 for conductor protection and Art 250 for grounding.

 

[tortuga]

Is it not center tapped hi-leg delta?

 

[jeff motta]

Is it not center tapped hi-leg delta?

It is a 240v center tapped high leg delta. 240V - 3phase 3- wire

 

[tortuga]

It is a 240v center tapped high leg delta. 240V - 3phase 3- wire

If its center tapped that would be what I call 4 wire.
Why not use the center tap and just do a single phase 120/240 panel for the 120V loads?

 

[LarryFine]

It is a 240v center tapped high leg delta. 240V - 3phase 3- wire

So, you have two 120v L-N lines now. How large is your expected 120 loading?

If relatively small, I agree. Just install a 1ph 120/240v panel from your existing service.

 

[jeff motta]

If its center tapped that would be what I call 4 wire.
Why not use the center tap and just do a single phase 120/240 panel for the 120V loads?

I could be wrong about the center tap, this is the older service now fed from the new 480 service, they have a 300kva 480v delta to 240v/120v delta transformer feeding a main 240 3phase 3wire distribution panel, then out to the older service. All of the older main service is fed only with 3phase 3wire (no neutral) and its original labeling says 3pahse 3wire, so again I may be wrong, that's why I'm here asking for help. I do like your suggestion.

 

[LarryFine]

I could be wrong about the center tap, this is the older service now fed from the new 480 service, they have a 300kva 480v delta to 240v/120v delta transformer feeding a main 240 3phase 3wire distribution panel, then out to the older service.

Check your 240v delta line-to-neutral voltages. You should have two at 120v and one at 208v.

 

[jeff motta]

So, you have two 120v L-N lines now. How large is your expected 120 loading?

If relatively small, I agree. Just install a 1ph 120/240v panel from your existing service.

Yes, A phase and C phase to ground = 120v B phase 208V to ground. This panel will be for 120v power, fans, lights, power for small machines possibly.

 

[LarryFine]

Yes, A phase and C phase to ground = 120v B phase 208V to ground.

Then you're golden. Install a 1ph panel using A, N, and C, ignoring B.

 

[jeff motta]

Then you're golden. Install a 1ph panel using A, N, and C, ignoring B.

Thats what I originally wanted to do, but when I opened the main panel, it lacks the neutral. All of the older 208v/120v panels have a 240v delta to 208v/120v transformer feeding the 208v120v panels.

 

[LarryFine]

Thats what I originally wanted to do, but when I opened the main panel, it lacks the neutral.

Can you add one? Can you find the transformer's secondary neutral?

 

[jeff motta]

Can you add one? Can you find the transformer's secondary neutral?

it would be too much work; they have parallel 4/0 - 3 conductor tray cable feeding the old service, that's why I am looking for info on sizing for the 240 delta to 208v/120v wye transformer set up.

 

[don_resqcapt19]

it would be too much work; they have parallel 4/0 - 3 conductor tray cable feeding the old service, that's why I am looking for info on sizing for the 240 delta to 208v/120v wye transformer set up.

The transformer protection rules are in Table 450.3(B) and the secondary conductor rules in 240.21(C).
The 200 amp breaker is fine for the primary protection.

 

[LarryFine]

Another option is a 240v-to-120/240v transformer to derive a new neutral.

 

[d0nut]

I could be wrong about the center tap, this is the older service now fed from the new 480 service, they have a 300kva 480v delta to 240v/120v delta transformer feeding a main 240 3phase 3wire distribution panel, then out to the older service. All of the older main service is fed only with 3phase 3wire (no neutral) and its original labeling says 3pahse 3wire, so again I may be wrong, that's why I'm here asking for help. I do like your suggestion.

It may also make more sense to feed your new transformer from the 480V service if the plant is trying to move away from the old 240V equipment they have. That way you aren't adding new loads to a system they are trying to remove.

 

[infinity]

Thats what I originally wanted to do, but when I opened the main panel, it lacks the neutral. All of the older 208v/120v panels have a 240v delta to 208v/120v transformer feeding the 208v120v panels.

I plan to come off the spare 200a breaker from the 240v delta panel, install a 75KVA 240 delta to 208v/120v wye transformer to feed the new power panel

If the 75 Kva works for you then just go with that.

 

[jeff motta]

It may also make more sense to feed your new transformer from the 480V service if the plant is trying to move away from the old 240V equipment they have. That way you aren't adding new loads to a system they are trying to remove.

I agree, I threw that out there but they are limited on 480v distribution and want to save any open space for future machines.

 

[tortuga]

I agree, I threw that out there but they are limited on 480v distribution and want to save any open space for future machines.

Another possibility if they don't have any older 120V loads that are voltage sensitive like incandescent lighting, is remove the 240 delta and replace it with a 220Y127 (you possibly could use a 208Y120 with a tap changer). The 220 would be likely high enough for the 240V equipment, and VFD's like a wye type voltage better than delta.
You would probably save about 3000kwh a year in transformer losses.

 

[ramsy]

remove the 240 delta and replace it with a (Y)

I thought a zigzag transformer was the only way to derive a neutral?

Would those (WYE)'s derive their own neutral, without a feeder neutral?