480 wye solar to 208 wye transformer connections 225kva

[harborrick]

Need a little guidance and clarification.
We have Solar Edge 480/277 20k inverters running to AC Panel Board 480v
Then to AC disconnect 480volt 3 phase 4 wire
From Disconnect to transformer 4 wires landing on H1,H2,H3 and XO
Using 2 new ground rods to XO creating neutral.
From other side of transformer I am bringing 3 phase 3 wire 208 volts to existing service with a AC disco in between
My question is do I need to bring another wire from XO to existing switchgear and if so where do I land.
I am already bring a equipment ground to existing ground buss?
Thank You in Advance
Project in California

 

[GoldDigger]

IMHO, unless you have phase loss protection to shut down the inverter(s), and maybe even then, you must supply a neutral to the 208Y/120 side of the transformer. That same neutral would then also connect to the 480V side and you would have a non-SDS configuration.
Not connecting the neutral on the POCO side of a three phase wye is only necessary when the other side is delta wound (or in some cases when it drives a three phase motor load.)

 

[Smart $]

IMHO, unless you have phase loss protection to shut down the inverter(s), and maybe even then, you must supply a neutral to the 208Y/120 side of the transformer. That same neutral would then also connect to the 480V side and you would have a non-SDS configuration.
Not connecting the neutral on the POCO side of a three phase wye is only necessary when the other side is delta wound (or in some cases when it drives a three phase motor load.)

Ummm... the other side appears to be delta configured. POCO-wye : PV-delta.

...
From Disconnect to transformer 4 wires landing on H1,H2,H3 and XO
...

No mention of H0.

 

[ggunn]

Ummm... the other side appears to be delta configured. POCO-wye : PV-delta.

It seems to me that it is the other way round, i.e. POCO delta 208 and PV wye 480/277.

 

[Smart $]

...
Then to AC disconnect 480volt 3 phase 4 wire
From Disconnect to transformer 4 wires landing on H1,H2,H3 and XO
...

It seems to me that it is the other way round, i.e. POCO delta 208 and PV wye 480/277.

Really???

 

[ggunn]

Really???

Yes, really. He has multiple SE 480/277V wye inverters that he wants to interconnect with a 208V service. He can do it either with a wye 480V to delta 208V isolation transformer or a 480V to 208V autotransformer. Either way, it has to be wye on the 480 side because the SE inverters need a grounded neutral.

 

[Smart $]

Yes, really. He has multiple SE 480/277V wye inverters that he wants to interconnect with a 208V service. He can do it either with a wye 480V to delta 208V isolation transformer or a 480V to 208V autotransformer. Either way, it has to be wye on the 480 side because the SE inverters need a grounded neutral.

An X0 terminal indicates the tranformer is wye on the low voltage side.

 

[jaggedben]

It seems to me that it is the other way round, i.e. POCO delta 208 and PV wye 480/277.

I agree. No mention of whether the POCO side has a neutral, and clear indication that inverters are to be wye/configured. In fact the OP is asking where he would land a neutral in the switchgear, which kind of suggests maybe there's no neutral bus over there? But then his mixture of 'H1,H2,H3 and XO' is confusing to me and suggests maybe he also doesn't have the right transformer.

My answer: Not enough info!

 

[jaggedben]

An X0 terminal indicates the tranformer is wye on the low voltage side.

Maybe he meant to say or HO, or maybe he doesn't have a suitable transformer, or maybe both sides are wye. Something doesn't jive.

 

[Smart $]

Maybe he meant to say or HO, or maybe he doesn't have a suitable transformer, or maybe both sides are wye. Something doesn't jive.

Ding, ding, ding.

At least one too many maybe's to say he's good to go. :happyyes:

 

[harborrick]

Maybe he meant to say or HO, or maybe he doesn't have a suitable transformer, or maybe both sides are wye. Something doesn't jive.

Utility side is 120/208 3 Phase 4 wire
480v inverters just need to see neutral created to transformer.
I will open transformer tomorrow and get more info.
I believe inverters just need to see the neutral on one side?
We have done it this way several times.
Our inspector was just asking some good questions about the return GEC to tie into existing switchgear.

 

[GoldDigger]

Utility side is 120/208 3 Phase 4 wire
480v inverters just need to see neutral created to transformer.
I will open transformer tomorrow and get more info.
I believe inverters just need to see the neutral on one side?
We have done it this way several times.
Our inspector was just asking some good questions about the return GEC to tie into existing switchgear.

You need to be very sure from the inverter spec whether it sources current to the neutral (in the event of unbalance for any reason) or whether it just uses the neutral for a voltage reference.
If you connect the inverter side of the transformer without a solid neutral the three wye voltages will tend to be equal whether or not the source wye voltages are equal (in the case of a delta wye transfomer). This can be either a good or a bad thing depending on how you look at it, and you need to know what the inverter wants to see.

If your transformer has X0 but no H0 it is a wye on the 208 side and a delta on the 480 side. That is not going to work for your inverter, AND you would have to leave the X0 floating on the input side because of the presence of a delta secondary.

You have a lot of checking to do and quite likely acquiring a different transformer.

 

[harborrick]

You need to be very sure from the inverter spec whether it sources current to the neutral (in the event of unbalance for any reason) or whether it just uses the neutral for a voltage reference.
If you connect the inverter side of the transformer without a solid neutral the three wye voltages will tend to be equal whether or not the source wye voltages are equal (in the case of a delta wye transfomer). This can be either a good or a bad thing depending on how you look at it, and you need to know what the inverter wants to see.

If your transformer has X0 but no H0 it is a wye on the 208 side and a delta on the 480 side. That is not going to work for your inverter, AND you would have to leave the X0 floating on the input side because of the presence of a delta secondary.

You have a lot of checking to do and quite likely acquiring a different transformer.

Transformer has a HO. Sorry I misspoke on original post.
I will be hooking up on solar end to H1.H2,H3 and HO(creating my neutral with 2 new rods hooking up to HO
Then parallel feeders to 800 amp disco with no neutral.
Just 2 equipment grounds back to new service .
So I believe inverter will see the neutral on 480 side HO (True)?

 

[GoldDigger]

So I believe inverter will see the neutral on 480 side HO (True)?

Yes indeed.

 

[mpd]

Did you check with Solaredge to find out if they have any specific transformer requirements and creating a neutral? I inspected a solar system about a year ago the inverter manufacture specified a specific transformer and a neutral was run from utility side to the transformer for the inverter neutral and the transformer was not to be installed with any ground to neutral connections at the transformer

 

[electricmonkpv]

SDS vs. non-SDS transformer connections for 3-phase inverters

SDS vs. non-SDS transformer connections for 3-phase inverters

IMHO, unless you have phase loss protection to shut down the inverter(s), and maybe even then, you must supply a neutral to the 208Y/120 side of the transformer. That same neutral would then also connect to the 480V side and you would have a non-SDS configuration.
Not connecting the neutral on the POCO side of a three phase wye is only necessary when the other side is delta wound (or in some cases when it drives a three phase motor load.)

I want to know more about ‘phase loss protection’ and what to consider in connecting inverters to transformers in general. I suppose phase loss protection relates to neutral current if a phase opens for some reason? Don’t the inverters just see unbalance voltage and cut out?


How does a Separately Derived System neutral arrangement affect inverter coupling to the grid? More stable? Less stable?






I’m connecting a Scott ’T’ 2-phase to 3-phase transformer to allow 3-phase, 208V / Wye inverters to feed to grid on a 2-phase system.


There are X0, X1, X2, X3 on the 3-phase side, and H0, H1, H2, H3, H4 on the 2-phase side (H1-2 is 240V, one phase and H3-4 is 240V another phase at 90deg). All 2-phase un-grounded conductors are 120V to ground.




The manufacturer, Hammond Power Systems, has recommended NOT connecting the H0 grounded conductor, and to operate the transformer as a separately derived system with X0 bonded to the transformer case and building grounding electrode system. The tech center guy was concerned about ‘circulating currents’ if H0 is used.

 

[GoldDigger]

Make sure the transformer documentation is compatible with wye type inverters.
Also make sure to recognize that the H side in this case is actually the secondary (inverter) side.
If the inverter is capable of sourcing current to the neutral, I do not see how you can possibly leave the wye center point on the inverter side disconnected.
As for phase loss, if one of the hot leads on the POCO side opened or shorted to neutral, I would certainly expect a unified three phase inverter to shut down.
But if you instead used three independent single phase inverters I would definitely not leave the wye point unconnected.

mobile

 

[jaggedben]

Also make sure to recognize that the H side in this case is actually the secondary (inverter) side.
...

I think you meant the opposite ... or something.

 

[GoldDigger]

I think you meant the opposite ... or something.

The high voltage side of the transformer is facing the 480Y/277 inverter(s) while the 208Y(/120?) side faces POCO.
And AFAIK the higher voltage side will be the H terminals, whether it is billed as a step-up or a step-down transformer.
How do you see it?

mobile

 

[jaggedben]

I'm looking at electromonkpv's post about connecting a 208 wye inverter to a 2phase system. Probably it should be the start of a new thread, but it looks to me like you overlooked his description.