Transformer configuration

[electro7]

Hi,

I am designing a 277/480V solar system (277/480V wye inverters). Service is 120/208V wye. Can I use a 277/480V wye to 208V delta transformer? Will the 208V delta side of the transformer work okay with the utility service voltage of 120/208 wye? Is the only difference that the 208V delta does not have a neutral?

Thanks ahead of time.

 

[ggunn]

Hi,

I am designing a 277/480V solar system (277/480V wye inverters). Service is 120/208V wye. Can I use a 277/480V wye to 208V delta transformer? Will the 208V delta side of the transformer work okay with the utility service voltage of 120/208 wye? Is the only difference that the 208V delta does not have a neutral?

Thanks ahead of time.

Yes; 480/277V wye to 208V delta is the way to go. Make sure the transformer is rated for step down operation; some are bidirectionally listed and some are not.

 

[electrofelon]

How many KW?

 

[electro7]

Thanks ggunn!

It is a 112.5 Kva. 105kw of solar.

 

[electrofelon]

Are you sure its worth installing a transformer vs using 208 inverters?

 

[electro7]

Are you sure its worth installing a transformer vs using 208 inverters?

Well if I remember correctly (need to double check with my distributor), the 208V inverters are quite a bit more expensive than the 277/480V and with the 208V I need about double the amount of strings.

But what are the typical percentage of losses in transformers? I thought maybe 2%. If that is the case I think it is quite a bit more cost effective for me to run with the 480V inverters and not worry to much about the 2%, or add 2% more of solar capacity to make up for the loss.

What are your thoughts?

 

[electrofelon]

Well if I remember correctly (need to double check with my distributor), the 208V inverters are quite a bit more expensive than the 277/480V and with the 208V I need about double the amount of strings.

But what are the typical percentage of losses in transformers? I thought maybe 2%. If that is the case I think it is quite a bit more cost effective for me to run with the 480V inverters and not worry to much about the 2%, or add 2% more of solar capacity to make up for the loss.

What are your thoughts?

I dont know off the top of my head about the inverter cost difference, you may well be correct that 208 is more expensive. Also 208 string inverters definitely dont come as large so you would need more of them. IIRC the best you can do is fronius 15KW symo, but that does do 1KV strings so the number of strings wouldnt be any greater. Of course you potentially save on the AC side wire with 480, but that depends on where the transformer goes.

I think you are about right to figure 2% load loss, but dont forget no load losses 24/7. Lots of variables for sure. I still have a bad taste in my mouth from a poorly designed job with transformers where they should have stuck with 208, but your situation could certainly be different.

 

[electro7]

I dont know off the top of my head about the inverter cost difference, you may well be correct that 208 is more expensive. Also 208 string inverters definitely dont come as large so you would need more of them. IIRC the best you can do is fronius 15KW symo, but that does do 1KV strings so the number of strings wouldnt be any greater. Of course you potentially save on the AC side wire with 480, but that depends on where the transformer goes.

I think you are about right to figure 2% load loss, but dont forget no load losses 24/7. Lots of variables for sure. I still have a bad taste in my mouth from a poorly designed job with transformers where they should have stuck with 208, but your situation could certainly be different.

What left you with a bad taste in your mouth regarding the poorly designed transformer job? So I can avoid the same mistake

 

[electrofelon]

What left you with a bad taste in your mouth regarding the poorly designed transformer job? So I can avoid the same mistake

This system was 100k ish. They used one transformer for each inverter and put them next to the inverters on the roof. I cant remember the inverter size and how many there were, it was either three or four. So we had all those transformers and associated disconnects, terminations, etc to make up and we didnt get the advantage of running 480 volts most of the way down to the electrical room. I could see transformers being worth it with ONE sitting next to the switchboard

 

[electro7]

This system was 100k ish. They used one transformer for each inverter and put them next to the inverters on the roof. I cant remember the inverter size and how many there were, it was either three or four. So we had all those transformers and associated disconnects, terminations, etc to make up and we didnt get the advantage of running 480 volts most of the way down to the electrical room. I could see transformers being worth it with ONE sitting next to the switchboard

I see. That defeats the purpose for the most part.

I agree with you, using one transformer near switchboard is best.