Is it possible to change delta to wye?

[shockking]

We have solar array with a single SMA Tripower Core1 33 kW inverter. The inverter goes to a small pad mount 45 kVA 480/208 step down transformer. Apparently we ended up with a transformer with delta on the 480 side, and the inverter is only compatible with 480/277 wye.

Is there a way to get this inverter working? Is our only option to replace the transformer?

 

[jaggedben]

Your only option is to replace the transformer.

Seems like you got the opposite of what you need. You got a 480D to 208Y 'step down' transformer. What you most likely want is a 208D to 480Y 'step up' transformer. At any rate, the manufacturer should approve of the 208 side being the side that energizes the transformer from the utility.

Good luck.

 

[GoldDigger]

Your only option is to replace the transformer.

There are other options, like adding a second transformer, but they would all be more expensive and less practical.

 

[tortuga]

Whats the make and model? You (or somone) can probably can just reconfigure it.

 

[GoldDigger]

Whats the make and model? You (or somone) can probably can just reconfigure it.

It is highly unlikely that one side of the transformer can be reconfigured from delta to wye at the same voltage.

 

[jim dungar]

Whats the make and model? You (or somone) can probably can just reconfigure it.

I have never seen a non-custom transformer that can be field reconfigured.

In my experience the secondary windings are almost always welded at the factory. Then there is the need to change the winding voltage ratio by a factor of 1.73.

 

[shockking]

Thanks all for the replies, much appreciated.

TLDR; after digging, my options are:
1) replace the 480D - 208Y/120 with a 480Y - 208Y/120, for which I was quoted $3.5k installed and 5 week lead time; or
2) add a second transformer, 480Y - 480D, quoted $4.8k installed with 3 day lead time.

The transformer we installed is:
ACME Electric general purpose Low Voltage Distribution Transformer - Three Phase, 480Δ - 208Y/120V, 45kVA
(catalog ID: T3045K0013B)

Seems in theory maybe it could be reconfigured from delta to wye... but I have not come across anyone who's ever heard of it being done. I'm betting @jim dungar is right that all else aside, the windings are likely factory welded in place (not field serviceable).

There's a short 50-foot run from the inverter to the interconnection. The building's service at the POI is 208Y/120. Output from the inverter 480/277 wye. The design intent was to run the 50-feet at 480V 3P3W (no neutral) to a step down transformer, and tie in from there. I don't think the engineer or electrician have much experience with solar and just overlooked that the inverter was wye only.

Two questions linger for me...
1) I don't fully understand what the issue is for the inverter; why does the inverter care if it's delta or wye? What measurement is there that it is able to tell the difference?
(note: the inverter can be used with our without neutral, but must be wye. It arrived from the factory with a bridge between the neutral terminal and the enclosure/ground for use without a neutral conductor to the POI.)

2) what should I do with this transformer if I replace it? It can't be returned now that we've punched holes in it... Ebay/craigslist? Anyone here want it?

 

[synchro]

This one says they have it in stock, but you'd need to verify that:

3-Phase 480 Y 277 - 208 Y 120 (Solar Transformer)

Primary Voltage: 480 Y 277 Secondary Voltage: 208 Y 120 (Solar Transformer) This design features a fully rated neutral on both primary and secondary sides commonly required in solar applications. The transformer can be fed with either 480 or 208 volts in a step up, or step down operation making...

store.maddoxtransformer.com

Adding a second transformer would add unnecessary losses and complexity, take extra room, etc.

 

[dkidd]

We have solar array with a single SMA Tripower Core1 33 kW inverter. The inverter goes to a small pad mount 45 kVA 480/208 step down transformer. Apparently we ended up with a transformer with delta on the 480 side, and the inverter is only compatible with 480/277 wye.

Is there a way to get this inverter working? Is our only option to replace the transformer?

Zig-zag transformer to get a neutral?

StackPath

 

[Carultch]

1) I don't fully understand what the issue is for the inverter; why does the inverter care if it's delta or wye? What measurement is there that it is able to tell the difference?
(note: the inverter can be used with our without neutral, but must be wye. It arrived from the factory with a bridge between the neutral terminal and the enclosure/ground for use without a neutral conductor to the POI.)

This particular inverter requires 277V to ground to operate, and its internal relay settings are based on the phase-to-neutral voltage. It can do its measurements from line-to-ground, so that you don't necessarily need to bring a neutral to it to properly function. However, it still needs the WYE grid in order to avoid the possibility of its components experiencing 480V to ground. While an inverter in general could be built with robust components to operate with 480V nominal to ground as is the most extreme you'll get on an ungrounded delta grid, this particular inverter isn't built for it. Its internal relay settings have a maximum amount you can adjust them to avoid overloading its internal components, and come standard with settings based upon the 277V value in a nominal 277/480V grid.

An ungrounded delta grid will not maintain the three phase voltages to be "equidistant" from ground. On occasion, the "triangle" may be centered, but it will not maintain this with enough stability to allow the inverter to operate. In order to ground the center of an existing ungrounded delta grid, you'd need a zigzag transformer or grounding transformer, to be used for establishing the neutral point as a reference to ground.

 

[shockking]

Makes sense. Thanks @Carultch

 

[jaggedben]

My gut tells me that waiting 5 weeks is well worth avoiding the efficiency losses accrued by an extra transformer over the life of the system.

 

[shockking]

That is a good point, thanks @jaggedben