Wye o wye.....

Status
Not open for further replies.
O

Open Neutral

Senior Member
Location
Inside the Beltway
Occupation
Engineer
I have 3 sync'ed 5KW inverters that put out 208/120 3ph. I need 480/277. Simple, just need a stepup transformer......But the 480 side feeds a remote Delta->Wye xfmr.

[When the inverters are not on-line, a PoCo xfmr feeds us from a wye. When Reddi Kilowatt goes on vacation, an ATS will switch from it to the inverters.]

I can't see any way around a Wye-Wye transformer, but know that brings a host of issues. Is there such a thing as Wye-Delta-Wye, or one with an aux. delta winding to control the harmonics?
 
Transformers aren't my forte, but can't you just feed the remote Delta transformer with 480 from your new step-up transformer? It doesn't need a neutral for its primary side, right? I don't see why it would care; 480 is 480.
 
The philosophical radio station: WYOY

Open Neutral said:
I can't see any way around a Wye-Wye transformer, but know that brings a host of issues. Is there such a thing as Wye-Delta-Wye, or one with an aux. delta winding to control the harmonics?
Click to expand...
A wye-primary transformer should be supplied as if it were a Delta primary. Just let the primary neutral (H0) float. You don't need to supply a primary neutral.
 
Open Neutral said:
I have 3 sync'ed 5KW inverters that put out 208/120 3ph. I need 480/277. Simple, just need a stepup transformer......But the 480 side feeds a remote Delta->Wye xfmr.

[When the inverters are not on-line, a PoCo xfmr feeds us from a wye. When Reddi Kilowatt goes on vacation, an ATS will switch from it to the inverters.]

I can't see any way around a Wye-Wye transformer, but know that brings a host of issues. Is there such a thing as Wye-Delta-Wye, or one with an aux. delta winding to control the harmonics?
Click to expand...

What voltage is the remote delta-wye secondary? If 208Y/120, why not tie the inverters into its secondary? ...voltage drop issues?
 
Smart $ said:
What voltage is the remote delta-wye secondary? If 208Y/120, why not tie the inverters into its secondary? ...voltage drop issues?
Click to expand...

It is 208Y/120.

The stepdown is 1100 ft away. Besides the stepdown, there are multiple 480 3ph motors there. We're at 480 to keep down the losses and costs down; even so, we're pulling 3*500 MCM, plus gnd & a neutral [in case a single phase 277 load emerges in the future...]

We could abandon that 277 possibility, but if we feed a delta primary with a delta source; then everything floats without constraint. I believe that is what's called "ill-advised".... {There's another issue that precludes such, which I'm skipping for now..}


[We priced out up-converting the Poco and inverter to 4160, and then down to 208Y; but it was $5K more with only slightly less loss, and the local electrician was sure the AHJ would have kittens over 4160 at a residence.]
 
LarryFine said:
A wye-primary transformer should be supplied as if it were a Delta primary. Just let the primary neutral (H0) float. You don't need to supply a primary neutral.
Click to expand...

See, that's what makes sense to me. Wire the 208 primary for Delta and then the secondary could be your 480/277, and the remote transformer can just take a 480 3? feed from there.

Yah?
 
Open Neutral said:
It is 208Y/120.

The stepdown is 1100 ft away. Besides the stepdown, there are multiple 480 3ph motors there. We're at 480 to keep down the losses and costs down; even so, we're pulling 3*500 MCM, plus gnd & a neutral [in case a single phase 277 load emerges in the future...]

We could abandon that 277 possibility, but if we feed a delta primary with a delta source; then everything floats without constraint. I believe that is what's called "ill-advised".... {There's another issue that precludes such, which I'm skipping for now..}


[We priced out up-converting the Poco and inverter to 4160, and then down to 208Y; but it was $5K more with only slightly less loss, and the local electrician was sure the AHJ would have kittens over 4160 at a residence.]
Click to expand...
Then a 208D to 480Y xfmr appears to be the best solution.
 
Smart $ said:
Then a 208D to 480Y xfmr appears to be the best solution.
Click to expand...

To fill in some of the additional factors....

1) So the standby three inverters each have a L and a N output terminal. I tie the N's together. Does that 3*N then float....? [I'm having a hard time picturing this today (little sleep last night), so if it's obvious, I apologize.]

2) On the 480 side, there are grid-tie inverters that put out 277 L-N.
They support the downstream loads both in PoCo & standby modes; and if there is excess output, they'll backcharge the standby inverters' battery string through the transformer in question. A problem or not?
 
Open Neutral said:
To fill in some of the additional factors....

1) So the standby three inverters each have a L and a N output terminal. I tie the N's together. Does that 3*N then float....? [I'm having a hard time picturing this today (little sleep last night), so if it's obvious, I apologize.]

2) On the 480 side, there are grid-tie inverters that put out 277 L-N.
They support the downstream loads both in PoCo & standby modes; and if there is excess output, they'll backcharge the standby inverters' battery string through the transformer in question. A problem or not?
Click to expand...
#1. N is required to be grounded.

#2. I don't see it as a problem.
 
Open Neutral said:
To fill in some of the additional factors....

1) So the standby three inverters each have a L and a N output terminal. I tie the N's together. Does that 3*N then float....? [I'm having a hard time picturing this today (little sleep last night), so if it's obvious, I apologize.]
Click to expand...
Oh, I didn't realize you meant three 1-ph units being combined as a wye source. I envisioned three paralleled units.

I'd clear it with the manufacturer, but yes, join (and bond, if not already done) the inverter out N's together, but supply the transformer as a Delta load.

2) On the 480 side, there are grid-tie inverters that put out 277 L-N.
They support the downstream loads both in PoCo & standby modes; and if there is excess output, they'll backcharge the standby inverters' battery string through the transformer in question. A problem or not?
Click to expand...
Hmmm. Now, we need to know if three wye-connected inverters can accept a Delta load as a recharging source. Again, the manufacturer should be consulted.
 
Open Neutral said:
To fill in some of the additional factors....

1) So the standby three inverters each have a L and a N output terminal. I tie the N's together. Does that 3*N then float....? [I'm having a hard time picturing this today (little sleep last night), so if it's obvious, I apologize.]
Click to expand...
[When the inverters are not on-line, a PoCo xfmr feeds us from a wye. When Reddi Kilowatt goes on vacation, an ATS will switch from it to the inverters.]
Click to expand...
When not on utility power, what keeps the three 1? inverter output voltages 120? apart?
 
Status
Not open for further replies.
Top