Solar wye/wye transformer

[electrofelon]

WYOY (101.7 FM, "Y101") is a contemporary hit radio station in Jackson, Mississippi. WYOY debuted in September 1996, and gave the Jackson area its first Top 40 station since 1993. Its studios are located in Ridgeland and the transmitter site is in Raymond.

 

[synchro]

"Why, why?"

Also:

http://library.industrialsolutions.abb.com/publibrary/checkout/White%20Papers%7CGET-3388B%7Cgeneric&usg=AOvVaw2Ao8Mgxni0VKnPz7C_rKbh

 

[electrofelon]

Also:

http://library.industrialsolutions.abb.com/publibrary/checkout/White%20Papers%7CGET-3388B%7Cgeneric&usg=AOvVaw2Ao8Mgxni0VKnPz7C_rKbh

Boring, would much rather listen to WYOY

 

[LarryFine]

WYOY (101.7 FM, "Y101") is a contemporary hit radio station in Jackson, Mississippi. WYOY debuted in September 1996, and gave the Jackson area its first Top 40 station since 1993. Its studios are located in Ridgeland and the transmitter site is in Raymond.

Oh, reality? Okay. I sometimes listen to WHYY in PA when I travel north. https://whyy.org/

WHYY-FM is a public FM radio station licensed to serve Philadelphia, Pennsylvania. Its broadcast tower is located in the city's Roxborough neighborhood at while its studios and offices are located on Independence Mall in Center City, Philadelphia.

 

[electrofelon]

Oh, reality? Okay. I sometimes listen to WHYY in PA when I travel north. https://whyy.org/

WHYY-FM is a public FM radio station licensed to serve Philadelphia, Pennsylvania. Its broadcast tower is located in the city's Roxborough neighborhood at while its studios and offices are located on Independence Mall in Center City, Philadelphia.

Yes I Am familiar. The NPR program "fresh air"is based out of WHYY and they say those call letters in the intro.

 

[jim dungar]

I wish people would just install delta->wye transformers for these. It just seems like some people think the wye-wye is "more grounded" or some other silly reasoning.

Invertors usually need a neutral point for their voltage reference. The supply to the building needs to have a neutral point, on their source, for Line-Neutral loads.

 

[electrofelon]

Invertors usually need a neutral point for their voltage reference. The supply to the building needs to have a neutral point, on their source, for Line-Neutral loads.

Just to be clear, for the purposes of this discussion I am referring to a customer owned <600 volt transformer, not the utility transformer supplying the premises. There are certainly valid reasons for wye wye on the utility and power distribution side. For this we would have to slog through that "the why's of the wyes paper", but again I prefer to just rock out to some WYOY FM!

 

[winnie]

Invertors usually need a neutral point for their voltage reference. The supply to the building needs to have a neutral point, on their source, for Line-Neutral loads.

But both of these needs can be provided by a conventional delta:wye transformer.

The building side neutral is provided by the supply transformer to the building.

Jon

 

[jim dungar]

But both of these needs can be provided by a conventional delta:wye transformer.

The building side neutral is provided by the supply transformer to the building.

Jon

Not when the invertor is the source.

 

[wwhitney]

Not when the invertor is the source.

Solar inverters are typically grid-tied, so that is generally the default for discussion unless other specified. And when grid-tied, the neutral is supplied by the utility, even when the energy comes from the inverter.

Cheers, Wayne

 

[synchro]

Solar inverters are typically grid-tied, so that is generally the default for discussion unless other specified. And when grid-tied, the neutral is supplied by the utility, even when the energy comes from the inverter.

Cheers, Wayne

And the inverters driving the wye side of a delta-wye won't create excessive circulating currents in the delta windings because the inverters function as current sources and are not establishing the AC voltage waveforms.

 

[electro7]

Dang, I didnt realize the complications with this configuration. Definitely making sure its a delta on the utility side next time.

The problem is I have 9 sites with these transformers. 4 of the sites will have a single pole 277V lighting circuit and a 2 pole 480V comm circuit which I will use phase a, b, and c for (I think is best for good balance for nuetral current in this sitiation, correct?). The other 5 sites will only have the 3 phase solar on the 480V side.

All sites have the 208V nuetral bonded to ground at the service. The problem I am seeing with connecting the nuetral to the XO and removing the XO bonding strap, and having the EGC on both the 480V side and 208V (Service) side bonded, is that they are bonded at the service and therefore means the HO neutral is connected to that same path. Am I thinking about that right? Not sure that is preferable.

Therefore I am back to leaving the nuetral conductor off on the XO terminal of the transformer. These are all customer owned transformers and are on the load side of the service (although some are line side taps with a fused disco). All the services are 208/120V wye.

The transformer manufacturer recommended leaving the nuetral XO (on the utility side) disconnected.

Any last thoughts?:/

Sent from my SM-N960U using Tapatalk

 

[wwhitney]

All sites have the 208V nuetral bonded to ground at the service. The problem I am seeing with connecting the nuetral to the XO and removing the XO bonding strap, and having the EGC on both the 480V side and 208V (Service) side bonded, is that they are bonded at the service and therefore means the HO neutral is connected to that same path.

And why is that a problem?

Both the 208V system and the 480V system need to have exactly one neutral-EGC bond. On the 208V side, that's at the service, so it's not allowed to create another one via bonding the transformer X0 to the case. While on the 480V side, you must supply the bond, like on any SDS.

Note that if you don't connect a 208V neutral to X0, and leave X0 bonded to the case and hence the EGC, then the EGC will carry the 208V neutral current the transformer requires to supply L-N loads on the 480V system. Which is not allowed, to use the EGC as a circuit conductor.

So as I understand it, the only choice is to bring the 208V neutral to X0 and to break the X0-case bond.

Cheers, Wayne

 

[jim dungar]

Solar inverters are typically grid-tied, so that is generally the default for discussion unless other specified. And when grid-tied, the neutral is supplied by the utility, even when the energy comes from the inverter.

Cheers, Wayne

Yes, but not all invertors are grid-tied.
I have done several that involve PV, battery walls, hydrogen generators, and natural gas generation and provide backup power as well as cogeneration.

 

[synchro]

The transformer manufacturer recommended leaving the neutral XO (on the utility side) disconnected.

That sounds like it might have a delta tertiary winding, in which case the neutral on the utility side should not be connected to X0. You should confirm whether this is the case. The nameplate should show if a tertiary is present.
If there isn't a tertiary winding then the neutral on the utility side needs to be connected to X0.

 

[wwhitney]

Yes, but not all invertors are grid-tied.

I don't see anything in the OP that would suggest that the inverters are dual-mode (hybrid), capable of operating in grid-tied mode or island mode with a grid disconnect device. But perhaps it's a mistake to assume the inverters are grid-tie only.

If I understand correctly, you are pointing out that if the inverters are dual-mode, then a delta 208V - wye 480V transformer wouldn't work for powering 120V loads on the 208V side from the inverters when the grid is disconnected? So a wye-wye transformer would be the logical choice in that case?

Cheers, Wayne

 

[wwhitney]

That sounds like it might have a delta tertiary winding, in which case the neutral on the utility side should not be connected to X0.

And X0 still gets debonded from the case, right? As otherwise the EGC provides a 208V neutral connection via the service neutral-ground bond.

Cheers, Wayne

 

[synchro]

And X0 still gets debonded from the case, right? As otherwise the EGC provides a 208V neutral connection via the service neutral-ground bond.

Cheers, Wayne

Yes, I agree.

 

[LarryFine]

So as I understand it, the only choice is to bring the 208V neutral to X0 and to break the X0-case bond.

That's how I see it, too. Wire it as you would any regular load.

 

[ggunn]

Invertors usually need a neutral point for their voltage reference.

Most of the commercial PV inverters I work with can use a neutral but do not require it. As delivered there is a strap bonding the neutral lug to ground that must be removed if a neutral conductor is run to the inverter.