wye to wye Step up/ step down transformer question

[joe.usip]

With a wye-wye, the line side star point can be connected. For a delta-wye with the delta on the inverter side, the line side star point should not be connected.
If a line side star point is not connected to a neutral it must also not be bonded/grounded.

I think this is where i was confused, because XO and HO are the same terminal, so by grounding one i am grounding both.

 

[GoldDigger]

I think this is where i was confused, because XO and HO are the same terminal, so by grounding one i am grounding both.

Fine for wye-wye, yes.

 

[PVfarmer]

Howdy y'all- I don't think that's an autoxfmr.
edit: DUH! I looked again. Type:Auto!

But still
My POCO doesn't allow autoxfmrs for connecting PV inverters, or they don't like it a lot.

The pic of the specs plate Joe posted listed primary and secondary.
There's no primary/secondary with an auto xfmr.

This autox goes from 480Y to 208Y:
http://www.temcoindustrialpower.com/products/Transformers_-_General/HT4438.html

This is the wiring diagram. I don't get it at *all*, but I do get how there's no pri/sec.
http://attachments.temcoindustrialpower.com/Wiring_diagram/transformer_wiring_HT_diagram14.pdf

This isolation xfmr looks more like the pic Joe posted.
http://www.temcoindustrialpower.com/products/Transformers_-_General/HT0585.html

It even has the Hs and Xs on Pri and Sec.
Wiring for previous link:
http://attachments.temcoindustrialpower.com/Wiring_diagram/transformer_wiring_HT_diagram35.pdf

So I think you're good, Joe! (I think?) You have the X0 on the inverter side (which the inverter has to have) and the H1 H2 and H3 are 208 L-L, so will be 120V L-N.

Anyone else? The inverter(s) neutral gets bonded/ground on the 480Y/sec side of Joe's xfmr, and the 208V from the "primary" (output) side of the xfmr gets bonded/grounded at the...600A disco?
I'm a little confused by @ parallel runs- should it be 3?

200 amp load center
to
fused 200 amp disconnect
to
XFMR, 2 parallel output runs
to
fused 600 amp disco, 2 parallel runs
to
line side tap at 1600 amp 208Y switchgear

 

[PVfarmer]

These are my rules- as you see, it's for "step-up".
Not sure why they put it in quotes.
But Joe step-down is what they are talking about here, as the "interface".


5.5.3 Primary and Higher Voltage Served DG Customers

The Company reserves the right to specify the winding connections for the Customer’s
“step-up” transformer between the Company’s delivery point and the Customer’s DG
facility’s output voltage as well as whether it is to be grounded or ungrounded. The
Customer shall provide their interface “step-up” transformer’s specifications and ratings
for the Company’s review in the impact and detailed studies.

5.5.3.1 Effectively Grounded, Four-wire Multi-grounded 3-phase Wye EPS:

The Company requires that all interface transformers be configured to have a
wye connected primary winding with a fully insulated neutral, and the secondary
winding to have a delta connection.

• If infeasible, an alternative that is subject to Company acceptance review is a
primary wye grounded - secondary wye grounded transformer requiring a
grounded source permitted under specified conditions.

 

[PVfarmer]

5 Solectria inverters ((3) 28TLs (2) 23Tls) 480Y output

Joe, I hate to say it but, you may have a problem here.

 

[GoldDigger]

Howdy y'all- I don't think that's an autoxfmr.
edit: DUH! I looked again. Type:Auto!

But still
My POCO doesn't allow autoxfmrs for connecting PV inverters, or they don't like it a lot.

The pic of the specs plate Joe posted listed primary and secondary.
There's no primary/secondary with an auto xfmr.

This autox goes from 480Y to 208Y:
http://www.temcoindustrialpower.com/products/Transformers_-_General/HT4438.html

This is the wiring diagram. I don't get it at *all*, but I do get how there's no pri/sec.
http://attachments.temcoindustrialpower.com/Wiring_diagram/transformer_wiring_HT_diagram14.pdf

This isolation xfmr looks more like the pic Joe posted.
http://www.temcoindustrialpower.com/products/Transformers_-_General/HT0585.html

It even has the Hs and Xs on Pri and Sec.
Wiring for previous link:
http://attachments.temcoindustrialpower.com/Wiring_diagram/transformer_wiring_HT_diagram35.pdf

So I think you're good, Joe! (I think?) You have the X0 on the inverter side (which the inverter has to have) and the H1 H2 and H3 are 208 L-L, so will be 120V L-N.

Anyone else? The inverter(s) neutral gets bonded/ground on the 480Y/sec side of Joe's xfmr, and the 208V from the "primary" (output) side of the xfmr gets bonded/grounded at the...600A disco?
I'm a little confused by @ parallel runs- should it be 3?

200 amp load center
to
fused 200 amp disconnect
to
XFMR, 2 parallel output runs
to
fused 600 amp disco, 2 parallel runs
to
line side tap at 1600 amp 208Y switchgear

The extra H and X taps on the autotransformer are likely voltage adjustment taps. Use instead of the ones listed to get either higher or lower ratio.

 

[GoldDigger]

Joe, I hate to say it but, you may have a problem here.

View attachment 13992

All that shows for sure is that the inverter side needs to be grounded wye. They draw a POCO side for completeness, but do not attach any words to it as they do for the secondary.

 

[PVfarmer]

All that shows for sure is that the inverter side needs to be grounded wye. They draw a POCO side for completeness, but do not attach any words to it as they do for the secondary.

Aren't the two thick black vertical lines an air gap?

 

[joe.usip]

All that shows for sure is that the inverter side needs to be grounded wye. They draw a POCO side for completeness, but do not attach any words to it as they do for the secondary.

This may be a dumb question, but do i still need to ground the neutral at the transformer to a ground rod even though the neutral is already grounded at the switch gear?

 

[PVfarmer]

This may be a dumb question, but do i still need to ground the neutral at the transformer to a ground rod even though the neutral is already grounded at the switch gear?

Not dumb at all- it's pretty confusing.
Try page 23?
http://www.mjobee.com/projects&news/delta xfmr1.pdf