240 delta with high leg solar installation

[jaggedben]

Allowed inverter shutdown time is different than fault clearing time on the transformer output time.

Then look at the trip curve of the breaker on the utility side.

Perhaps what you're not understanding is that the available fault current from the utility is at least two orders of magnitude greater than the inverter output. So for most portions of the trip curve the inverter is going to be a rounding error. The code does not require it to be addressed. By the way, this question also has nothing to do with the fact that there is a transformer in the system design. You could be asking the same thing about any inverter output connection.

 

[PVfarmer]

The array could have a GEC but it's entirely irrelevant to what's been mentioned so far.

See UL 1741.

Does UL 1741 say anything about following the installation manual?
I'd say the installation manual is pretty darn relevant, including the part where a 3 phase 240V grid of any kind is not listed as "supported".

I don't get the inspector's issue with faults, but this seems fairly straightforward.

 

[jaggedben]

I think the manufacturer has the final say on interpreting their own manual. And I could be wrong, but I believe they'd say this install is okay. The fact that the manual might use the word 'grid' when it means 'AC system' shouldn't by itself be a show stopper, in my opinion, if the manufacturer confirms what they really meant. It would have been prudent for the designer to check with SolarEdge. But again, unless we find out from the OP that this is the inspector's real objection, let's not belabor the point too much.

 

[PVfarmer]

I think the manufacturer has the final say on interpreting their own manual.

And I could be wrong, but I believe they'd say this install is okay.

The fact that the manual might use the word 'grid' when it means 'AC system' shouldn't by itself be a show stopper, in my opinion, if the manufacturer confirms what they really meant.

But again, unless we find out from the OP that this is the inspector's real objection, let's not belabor the point too much.

I don't see what there is to interpret- high-leg isn't listed.

I don't see how you can connect the 208V orange conductor of a high-leg service to a 240V delta xfmr for stepped-down PV output.

It doesn't list high-leg no matter what you call it. The inverter needs the neutral from the grid for reference, and the loads use that same neutral (in the MSP as described).

Sure, I can't explain what it has to do with faults/breakers tripping.
But when the POCO's xfmr is delivering 208V on the high leg, how can it receive 240V from PV?

The OP could perhaps solve the issue by changing the service to plain 240 delta and adding/using a 240D -> 240/120CT xfmr for loads.

 

[PVfarmer]

The OP could perhaps solve the issue by changing the service to plain 240 delta and adding/using a 240D -> 240/120CT xfmr for loads.

Pardon me, too late to edit- that's if 240 delta is ok with SolarEdge. And of course the POCO and inspector too.

 

[jaggedben]

The OP has connected the inverter to a 480/277 Wye. There happens to be a transformer between that system and the service. But there is always a transformer somewhere up the line. It's just often on the utility's side of the service point. So if it's okay to connect an inverter to a 480/277 Wye 'grid' when you have no idea what the utility transformer is, then it should be okay to connect to a 480/277 Wye SDS when the other side of the transformer is approved by an engineer.

There's no reason a high-leg can't be connected to the delta side of a transformer designed for that purpose. It's called a high-leg delta for a reason. The high-leg is 208V to ground, and 240V to the other phase conductors.

 

[ggunn]

Does UL 1741 say anything about following the installation manual?
I'd say the installation manual is pretty darn relevant, including the part where a 3 phase 240V grid of any kind is not listed as "supported".

It's not connected to a 240/120V high leg service, it's connected to a 480/277V transformer that is connected to a 240/120V high leg service. As far as the inverter is concerned, it's connected to a 480/277V service. I do this frequently and it works fine.

 

[PVfarmer]

Guys...
CAUTION! tends to get my attention.

Page 36:
GridConnectionGuidelines
NOTE Three phase inverters require
neutral connection at all times (only WYE type grids with neutral
connection are supported).


When connecting multiple single phase inverters in an
installation connected to a three-phase grid, phase
balancing may be required by the utility or grid operator.

Page 37:
CAUTION!
The only supported Delta grid is the 208V L-L grid.
Connecting the inverter to other Delta grids
may damage the inverter and will
void the warranty.


To set the inverter for
Delta grid connection,
you must move
the fuse from the
WYE fuse holder, marked as Y GRID,
to the Delta fuse holder, marked
as ∆ GRID.
https://www.wholesalesolar.com/cms/solaredge-se14400us-208-installation-manual-3800765590.pdf

 

[ggunn]

Guys...
CAUTION! tends to get my attention.

Page 36:
GridConnectionGuidelines
NOTE Three phase inverters require
neutral connection at all times (only WYE type grids with neutral
connection are supported).


When connecting multiple single phase inverters in an
installation connected to a three-phase grid, phase
balancing may be required by the utility or grid operator.

Page 37:
CAUTION!
The only supported Delta grid is the 208V L-L grid.
Connecting the inverter to other Delta grids
may damage the inverter and will
void the warranty.


To set the inverter for
Delta grid connection,
you must move
the fuse from the
WYE fuse holder, marked as Y GRID,
to the Delta fuse holder, marked
as ∆ GRID.
https://www.wholesalesolar.com/cms/solaredge-se14400us-208-installation-manual-3800765590.pdf

What has all this got to do with anything? Most of us who do this for a living know what inverters will and won't connect to what services and what we need to do for POCO compliance. BTW, What you have cut and pasted must be from a particular inverter's documentation; not all three phase inverters require a neutral connection. The SMA 30kW Tripower is an example of such an inverter.

Anyway, I believe that even the most naive designers knows not to connect a 208V inverter to a 480V service or vice versa.

 

[PVfarmer]

The high-leg is 208V to ground

There's no reason a high-leg can't be connected to the delta side of a transformer designed for that purpose.

The high leg is supposed to be marked orange because it is 208V, to ground *and* neutral.

But in the pic posted in post #10 of the "PV to service panel" xfmr, the xfmr is *not* designed for that purpose- there no neutral, it is 240V delta.
The OP also said: "On the service side of the xfmr, there is no neutral connection. There is one on the inverter side, but not service side."

This below is talking about how the inverter neutral must be connected to WYE grid neutral, I don't see how the 480Y/277V side of a PV step down transformer counts as grid if the neutral ends there.

Seems like the 9kw and 14.4kw are OK for delta-

AC Output Line Connections
4-wire WYE (L1-L2-L3-N) plus PE or 3 wire Delta
https://www.solaredge.com/sites/default/files/se-three-phase-us-inverter-208V-datasheet.pdf

But not the 20 or 33.3kW-

AC Output Line Connections
4-wire WYE (L1-L2-L3-N) plus PE
https://www.solaredge.com/sites/default/files/se-three-phase-us-inverter-datasheet.pdf

NOTE Three phase inverters require neutral connection at all times (only WYE type grids with neutral connection are supported).

 

[PVfarmer]

What has all this got to do with anything?
What you have cut and pasted must be from a particular inverter's documentation;

Um....yeah.
If you would have clicked the link right next to the pasted stuff, you would have seen it's from the actual installation manual for the inverter the OP is using, as far as I know. OP- "We are using a SolarEdge 33k 480v inverter. "

And yes, the SMA 30kW can connect @ 480V delta- the others, 24kw, 20kw, 15kw and 12kW are 480Y.
I knew that already.
I posted the link a while back in this thread, in fact.
It's the bottom left corner- if you have a "stinger ground" (high-leg) grid, you must use SMA 5.0, 6.0. 4548-US or 6048-US inverters.
http://files.sma.de/dl/1380/COMMONTXCONFI_AUS161222W.pdf

The point is that the LV side of the step down xfmr for the PV should be the same as the service voltage/LV side of grid transformer.

240 delta (from PV) with no neutral simply isn't the same as 240/208/120 high leg service.

 

[ggunn]

240 delta (from PV) with no neutral simply isn't the same as 240/208/120 high leg service.

But it is. The 240V delta part (the phase to phase voltages) of that service is exactly the same. The voltages to ground of the three phases of the service have nothing to do with the voltages to ground on the 480V side of the transformer; that's what separately derived means. A 480/277V wye to 240V delta transformer, even if the 240V service is high leg, will work just fine; the neutral isn't used. I have several systems installed and running set up exactly that way.

One thing that you do have to be careful of, however, is to be sure that the POCO's transformer driving the high leg will take 1/3 of the power from the PV. Many high leg services are set up with a much smaller high leg driver, and if your PV system is "large" you could overload it.

 

[acrwc10]

I think this has gone way off track from what the OP stared. As I read it the issue is the transformer output flowing to the service is an ungrounded delta, the service it is connected to is a 240 Y. if there is a ground fault between the transformer and the service, the interconnecting OCPD at the service will trip. but the PV output will still be feeding the transformer until it sees the power outage on the utility side. The PV will be feeding the fault until shut down occurs in the inverter. How long would be an acceptable time for this to go on?

 

[jaggedben]

I think this has gone way off track from what the OP stared. As I read it the issue is the transformer output flowing to the service is an ungrounded delta, the service it is connected to is a 240 Y.

It is a grounded delta, and it is a high-leg not a wye.

Please quit using the phrase 'transformer output'. It has no meaning when there are sources on both sides. Either side could of the transformer could output energy depending on what is hooked to it.

if there is a ground fault between the transformer and the service, the interconnecting OCPD at the service will trip. but the PV output will still be feeding the transformer until it sees the power outage on the utility side. The PV will be feeding the fault until shut down occurs in the inverter. How long would be an acceptable time for this to go on?

SEE UL 1741.

We are talking a fraction of a second here.

 

[acrwc10]

It is a grounded delta, and it is a high-leg not a wye.

Please quit using the phrase 'transformer output'. It has no meaning when there are sources on both sides. Either side could of the transformer could output energy depending on what is hooked to it.



SEE UL 1741.

We are talking a fraction of a second here.

I use the term "output" just so you know what side of the transformer I am referring to. Yes the transformer could output on both sides, that is obvious, but the PV is feeding into it and is not a load, so that is irrelevant to the conversation. You say "a fraction of a second"! based on what? your experience? or did you get that from the inverter manufacturer?

 

[Smart $]

Does UL 1741 say anything about following the installation manual?
I'd say the installation manual is pretty darn relevant, including the part where a 3 phase 240V grid of any kind is not listed as "supported". ...

That's the whole point of the transformer... converting from a non-supported grid to a supported "grid".

 

[PVfarmer]

The voltages to ground of the three phases of the service have nothing to do with the voltages to ground on the 480V side of the transformer; that's what separately derived means.

I have several systems installed and running set up exactly that way.

One thing that you do have to be careful of, however, is to be sure that the POCO's transformer driving the high leg will take 1/3 of the power from the PV. Many high leg services are set up with a much smaller high leg driver, and if your PV system is "large" you could overload it.

The fact is that the installation manual for the OP's inverter says neutral is required. It can't end on the PV side of the PV xfmr.
It need the grid neutral to operate correctly- you can't turn off neutral sensing in a SE 33.3kW inverter.

Seems like the OP described the neutral as a GEC.
Isn't it actually a SBJ? (or possibly a SSBJ, I can't picture the diagram in my head)

On the service side of the xfmr (240 delta), there is no neutral connection. There is one on the inverter side, but not service side. The GEC is tied continuously from the array, through the inverter, through the disconnect,through the xfmr which is also tied to the neutral on the inverter side of xfmr, through the disconnect, and tied the the ground/neutral bar at the service.

I think this has gone way off track

Couldn't not having the neutral connected properly cause the inspector's issue?

It is a grounded delta, and it is a high-leg not a wye.

Please quit using the phrase 'transformer output'.

I'd say the AC PV output is still output after going thru the xfmr, for discussion purposes at least.

As explained by the OP, it seems the inverter neutral is tied to the center-tapped service neutral. (red part above). Maybe that is the problem.

 

[PVfarmer]

That's the whole point of the transformer... converting from a non-supported grid to a supported "grid".

I realize that. If the OP's service was 480Y/277V, there would still be a xfmr owned by the POCO to step up the inverter to MV grid voltage.

But the service is this:
http://forums.mikeholt.com/attachment.php?attachmentid=7057&d=1340325879

I'm assuming the main service panel has orange-marked high-leg conductors for bus B (leg X1/208V in the above pic).
What I'm not seeing is how bus B can be connected at 208V to the POCO xfmr and also be 240V when connected to 1 of 2 windings of the 240 delta side of PV xfmr.

 

[Smart $]

I realize that. If the OP's service was 480Y/277V, there would still be a xfmr owned by the POCO to step up the inverter to MV grid voltage.

But the service is this:
http://forums.mikeholt.com/attachment.php?attachmentid=7057&d=1340325879

I'm assuming the main service panel has orange-marked high-leg conductors for bus B (leg X1/208V in the above pic).
What I'm not seeing is how bus B can be connected at 208V to the POCO xfmr and also be 240V when connected to 1 of 2 windings of the 240 delta side of PV xfmr.

B is 208V to the grounded neutral. It is also 240V to A and 240V to C. That's all the "PV" transformer needs is A, B, and C at 240V to each other.

 

[jaggedben]

I use the term "output" just so you know what side of the transformer I am referring to. Yes the transformer could output on both sides, that is obvious, but the PV is feeding into it and is not a load, so that is irrelevant to the conversation. You say "a fraction of a second"! based on what? your experience? or did you get that from the inverter manufacturer?

Yes, it's based on my experience. I've never disconnected a utility interactive inverter from the utility and had to wait any amount of time in which I could do anything else before the inverter side conductors became de-energized. I've seen the power reading change instantly on meters.

But also: SEE UL 1741. I believe that's the document that definitively answers you're question 'how long is acceptable for the inverter to output power' once the primary source is disconnected. The existence of a transformer makes no meaningful difference to how long it takes.

FYI, the inverter's algorithims may detect the fault and shut off the inverter faster than the utility side circuit breaker.

The fact is that the installation manual for the OP's inverter says neutral is required. It can't end on the PV side of the PV xfmr.

That last sentence is exactly backwards. The neutral for the PV side SDS must end at the PV side of the xfmr. Any further connection from there is considered an SSBJ or a GEC and is not supposed to carry any current.