480/277 WYE service to 120/240 Single phase

[ggunn]

Pretty sure you don't want to, or even if it's possible, to connect Tripowers at 480V.

???

480/277 is the native output AC voltage of a Sunny Tripower.

http://files.sma.de/dl/21561/STPTL-US12-24-DUS153313W.pdf

 

[jaggedben]

<sigh> :slaphead:

 

[PVfarmer]

???

480/277 is the native output AC voltage of a Sunny Tripower.

http://files.sma.de/dl/21561/STPTL-US12-24-DUS153313W.pdf

But the only way you can use 480V is with an extra transformer, according to page 6 and 7 here.
http://files.sma.de/dl/7418/STP24-US_MV_Trafo-TI-en-10.pdf

And on page 69 here, they're rated 20,000 watts at 277V.
http://files.sma.de/dl/21561/STP12-24TL-US-IA-en-16W.pdf

Also, page 39 there ^^, all the voltage parameters are based on 277V.

However, the Tripower 60 model connects at 480V delta.
http://files.sma.de/dl/25977/STP60-US_EXP_DUS151619W.pdf

edit: correct me if I'm wrong of course- it wouldn't be the first time.

 

[jaggedben]

But the only way you can use 480V is with an extra transformer, according to page 6 and 7 here.
http://files.sma.de/dl/7418/STP24-US_MV_Trafo-TI-en-10.pdf

That document does not say that if the service is 480/227 that an additional transformer is required. The delta examples in the diagrams are not 480/277 wye.

And on page 69 here, they're rated 20,000 watts at 277V.
http://files.sma.de/dl/21561/STP12-24TL-US-IA-en-16W.pdf

Also, page 39 there ^^, all the voltage parameters are based on 277V.

Yes, and two lines below that it says the output is 480/277 Wye.

A wye system has both line-line and line-neutral voltages. You should try to understand that.

However, the Tripower 60 model connects at 480V delta.
http://files.sma.de/dl/25977/STP60-US_EXP_DUS151619W.pdf

Interesting, but not relevant.

edit: correct me if I'm wrong of course- it wouldn't be the first time.

Finally you're right about something.

 

[PVfarmer]

That document does not say that if the service is 480/227 that an additional transformer is required. The delta examples in the diagrams are not 480/277 wye.

Yes, and two lines below that it says the output is 480/277 Wye.

It appears to say that you want to connect to the grid at 277V / wye on the LV / inverter side and then delta on the HV side, preferably.
In the diagrams at the bottom of page 3 and 4, there are 3 inverters- L1 of each connected to "leg A" of the wye xfmr, L2 of each to "leg B", and L3 to "leg C", and neutral from all three to the neutral on the xfmr.
So that's 277V, and the inverters are connected the same way in the delta example (meaning wye on the inverter side)
Doesn't the delta example also say both xfmrs have to be sized 2x the output of the inverters?

That 2x thing is stated as- Spv <= 0.5 Sxfmr_LV and Spv <= 0.5 Sxfmr_MV in the delta example.
Whereas the one on pages 3 and 4, the recommend ones, which are wye to wye (neutral on both sides of zfmr/s) and wye to delta, are Spv<= 0.9 Sxfmr_MV.
And the "restrictively recommended" one, wye to wye with no neutral on the MV side, is Spv <= 0.1 Sxfmr_MV, or xfmrs sized 10x the PV output.

Wouldn't you want to make any inverter to LV xfmrs for supplying a load the same voltage and wiring (wye) as the LV to MV xfmrs?

I understand, if you put 2 of the legs from a Tripower together, you get 480V...but it doesn't seem like you are supposed to do that.

 

[jaggedben]

It appears to say that you want to connect to the grid at 277V / wye on the LV / inverter side and then delta on the HV side, preferably.

A wye system has L-L and L-N voltages. Common voltages in the US are 480/277 Wye (that's 480V L-L with 277V L-N) and 280/120. 277V/wye doesn't really mean anything. The OP on this thread clearly tilted the thread "480/277 WYE service". The SMA datasheets say the same thing.

In the diagrams at the bottom of page 3 and 4, there are 3 inverters- L1 of each connected to "leg A" of the wye xfmr, L2 of each to "leg B", and L3 to "leg C", and neutral from all three to the neutral on the xfmr.
So that's 277V, and the inverters are connected the same way in the delta example (meaning wye on the inverter side)

Again, it's 277 L-N and 480 L-L. It's a 480/277 Wye, just like it says in the inverter spec sheet.

I understand, if you put 2 of the legs from a Tripower together, you get 480V...but it doesn't seem like you are supposed to do that.

You don't understand. If you measure from one hot leg to another you get 480V, and that's exactly what you're supposed to get. If you don't have 480V line-to-line, you've connected to the wrong type of system and the inverters won't function. (BTW, you don't 'put 2 legs ... together'. That creates an explosion. I guessing at what you meant there.)

 

[GoldDigger]

The tripower could be designed to deliver current only line to line, with the neutral only there for checking the system balance, as is done with many 120/240 single phase GTIs do. Or it could be designed to deliver current line to neutral, and the availability of the delta connection is not significant.
Does anyone know for sure how the Tripower is built?

 

[jaggedben]

Evidently it requires the neutral and, unlike some inverters, cannot be programmed to work without it. The fact that the specs give the current output at 277V suggests it delivers current line-to-neutral.

As PVfarmer pointed out, the 60kW version appears to be different in this respect.

I'm not sure I can wrap my head around what the difference really means.

 

[PVfarmer]

Evidently it requires the neutral and, unlike some inverters, cannot be programmed to work without it. The fact that the specs give the current output at 277V suggests it delivers current line-to-neutral.

As PVfarmer pointed out, the 60kW version appears to be different in this respect.

I'm not sure I can wrap my head around what the difference really means.

The only thing I can think of is, say you had a 480V 3 phase well pump or something.
The Tripower manual says "any load between the inverter and xfmr(s) has to be separately breakered", so you could run that (solidly grounded) 480V pump off of the Tripower(s) and it would be well-balanced.
So if the pump was 1.5 hp or 1119 watts you'd only be taking 1119/3 watts from each leg.

But I don't get what that means as far as the "neutral reference" that the Tripowers need to have.
Can anyone translate "neutral leading outwards" from the SMA manual?
I read it as "connected electrically but only carrying fault current". And perhaps "imbalance current" if that makes any sense.

And (I think) you wouldn't want to use only L1 to L2 from the inverter for a single 480 to 120/240 xfmr/load, as that would unbalance the inverter(s) output somehow.

So if you had a small 277V load, you could do the same sort of thing as the well pump idea by tapping into all three legs and neutral and using that for a 277/480V panel.
But a 277/480V panel would have to be perfectly balanced to not upset the inverter(s), whereas if you had *isolation* xfmr(s) going 277V wye to 480V delta (or 240 D, or 208Y/120...) the isolation feature of the xfmr(s) keeps any imbalance on the side where it occurs?

Did that thing I mentioned earlier make sense, about having three single phase 277V to 120/240V xfmrs connected on Tripower side at 277V wye and then L1 from each xfmr to L1 in the load panel for 120V loads, and L2 of each xfmr to L2 in the panel, and all 3 xfmr neutrals to the panel neutral? And then L1 and L2 give you your 240V.
That way all three xfmrs would be supplying any loads as equally as possible. I think. I have a one line diagram if anyone wants to see it.
It would also make the "load xfmrs" the same voltage as the to-grid xfmr(s), 277V.

Pretty sure where I am, 200A 208/120V service is three 25 kVA 12.47kV (delta) to three legs of 120V to neutral and/or 208 line-to-line.
So if I can get 100A of 480/277V, it would be three 30 kVA 12.47kV (delta) to three legs of 277 to N and/or 480 L-L.
But the Tripowers don't want to connect at the 480V, they want the "neutral leading out", meaning N connected to a xfmr, and the xfmr also being grounded, I believe.

My guess is that the wye to wye and/or wye to delta "recommended" (by SMA) xfmr(s) setup ensures that any inverter to grid (or inverter to load?) connections are balancing out, so you would want to do the same when connecting any load (like the water pump idea) before or after the xfmr(s).

 

[jaggedben]

PVfarmer, there's so many problems with your last post (and others) that its not worth responding in detail.

You keep talking about connecting to 'inverters' which is wrong thinking. Both loads and interactive-inverters must connect to a system with the right voltage and configuration. Generally that system is either the utility service (supplied from a utility transformer that you don't need to know anything about), or a separately derived system, a.k.a transformer connected to another system. (I'm leaving out stand-alone systems here and the Tripowers are not intended to work with them.)

Neither loads nor inverters have to be perfectly balanced, although there are restrictions on how unbalanced inverters can be. Balancing loads just ensures you are not wasting capacity and efficiency in the system. Unbalanced loads do not 'unbalance' in inverters output. The output that is not used within the system or service will be exported to other systems or to the grid.

Tripowers have to connect to a 480/277V wye system. Discussing whether they connect 'at 480V' or 'at 277V' is pretty much a nonsense discussion, notwithstanding academic questions about how they are internally configured. It makes no difference to anything else connected to the system.

Whatever SMA means by 'neutral leading outwards', I'm positive it's not either of the things you suggested. I think they are just trying to communicate that it must be what we call a Wye system, with a neutral connected at the center of all three windings. I guess in some other English speaking countries they call it a 'star system', so maybe the Germans were just unsure of what terminology to use.

 

[ggunn]

So if you had a small 277V load, you could do the same sort of thing as the well pump idea by tapping into all three legs and neutral and using that for a 277/480V panel.
But a 277/480V panel would have to be perfectly balanced to not upset the inverter(s)...

But for the inverter to run it must be connected to the grid, and if it's connected to the grid who cares if the local load is balanced or not?

 

[PVfarmer]

You keep talking about connecting to 'inverters' which is wrong thinking. Both loads and interactive-inverters must connect to a system with the right voltage and configuration. Generally that system is either the utility service, or a separately derived system
---
there are restrictions on how unbalanced inverters can be.
Unbalanced loads do not 'unbalance' in inverters output. The output that is not used within the system or service will be exported to other systems or to the grid.
---
Tripowers have to connect to a 480/277V wye system.It makes no difference to anything else connected to the system.
I think they are just trying to communicate that it must be what we call a Wye system, with a neutral connected at the center of all three windings.

I'm not sure what to call it besides "connecting"- the inverter has L1, L2, L3, N, and PE....connections. It says "Output Phases - 3 / Line Connections - 3-N-PE" on the spec sheet. PE for Primary Earth (or ground), I believe.
--
An off balance load wouldn't affect the inverter(s) overall output, but it would affect the grid interaction and balance. It mentions those issues in the National Grid interconnection booklet.
For instance- if you used a 480V to 120/240V xfmr for the load, running from L1 and L2 of the Tripower(s), and current from L1,L2 and L3 of the TPs is normally going out to the grid at 3 x 277V (when there's no load), when the welder starts going on and off, L1 and L2 (at 480V) could end up using current from the grid- then where does L3 go?
---
This is pasted from page 2 of the link. If N is required, how can you get 480V, when you only get 480V by not using the N?
The voltage on the low-voltage side must be 3 x 277 V/480 V. A neutral point is required and must lead outward as a neutral conductor.
http://files.sma.de/dl/7418/STP24-US_MV_Trafo-TI-en-10.pdf

 

[kwired]

But for the inverter to run it must be connected to the grid, and if it's connected to the grid who cares if the local load is balanced or not?

Far from being a PV expert myself, but that is my understanding of them - if the unit is say 35 kW, it puts out 35 kW - if there is enough sun/storage in battery to reach full power anyway. If a local load uses less then 35 kw, then the remainder is metered out into the grid, if the local load is more then 35 kw then there is net consumption from the meter from the grid. If local load is unbalanced - inverter is still putting out 35 kw, it just depends on what is going where when it comes to metering usage/input to grid. The utility transformer is setting voltage and phasing - the inverter is just matching up to it.

 

[GoldDigger]

To me "must lead outward" is a statement that any wye center point must not be isolated but must ultimately connect to a service or supply neutral. (That is, outward means away from the inverter connection point.)
One thing that is not clear from this is whether they would allow connection of the inverter to an SDS, where the wye point is grounded but not connected directly to POCO neutral.
My gut reaction is that this would be allowed, but that an ungrounded wye source would not be. Nor would a connection to a grounded wye be allowed where only the three hot conductors from the source are present, even if a locally derived neutral is provided via a zig-zag transformer.

The distinction actually makes sense when POCO uses a grounded wye secondary but does not run a neutral.
NEC requires a neutral when line to neutral loads are present, but the GTI is not a load.

 

[PVfarmer]

But for the inverter to run it must be connected to the grid, and if it's connected to the grid who cares if the local load is balanced or not?

The powers that be reserve the right to charge ya if things aren't up to "specs".

1. Customer generation connected to the distribution system can cause a variety of system
impacts including steady state and transient voltage changes, harmonic distortion, and
increased fault current levels. Parallel generation systems, which located individually on
higher capacity feeders may not cause very serious impacts, can, on weaker circuits, in
aggregation or in special cases (such as lightly loaded networks), significantly impact the
Company’s Distribution EPS.
2. An Impact Study and a Detailed Study in some cases is needed to identify the severity of
system impacts and the upgrades needed to avoid problems on the Company Distribution
EPS. Typically, an Impact or Detailed Study will be performed by the utility to determine if
the proposed generation on the circuit results in any relay coordination, fault current, and/or
voltage regulation problems.
3. There is a wide range of potential issues associated with the interconnection of DG facilities
to the Company Distribution EPS including, but not limited to:
• Impact on step voltage regulation equipment
• Increased fault duty on Company circuit breakers
• Interference with the operation of protection systems
• Harmonic distortion contributions
• Voltage flicker
• Ground fault overvoltages
• Islanding
• System restoration
• Power system stability
• System reinforcement
• Metering
4. It is important to scrutinize the interconnection of Customer DG facilities to the Company
Distribution EPS so that any negative impacts can be avoided and assure that the customer
generation will have only a positive or, at least, neutral impact on the EPS performance. It is
the intent of any Company study in accordance with SCDG requirements when applicable to
avoid negative power system impacts by identifying the particular type of impact that will
occur and determining the required equipment upgrades that can be installed to mitigate the
issue(s)

 

[jaggedben]

I'm not sure what to call it besides "connecting"- the inverter has L1, L2, L3, N, and PE....connections. It says "Output Phases - 3 / Line Connections - 3-N-PE" on the spec sheet. PE for Primary Earth (or ground), I believe.

Dude, read what I said again. This time I'll bold the important parts for you.
"Both loads and interactive-inverters must connect to a system with the right voltage and configuration. Generally that system is either the utility service, ... or a separately derived system,"

In the next quote you talk about "a load running from L1 and L2 of the Tripowers". That's crazy talk. You connect the load to L1 and L2 of the system. You connect the Tripowers to L1,2,3 and N of the system. If you only connect a load to the Tripowers nothing will work.

An off balance load wouldn't affect the inverter(s) overall output, but it would affect the grid interaction and balance. It mentions those issues in the National Grid interconnection booklet.

As I said, there are limits on the size of imbalance. That is not the same as imbalance being prohibited.

For instance- if you used a 480V to 120/240V xfmr for the load, running from L1 and L2 of the Tripower(s), and current from L1,L2 and L3 of the TPs is normally going out to the grid at 3 x 277V (when there's no load), when the welder starts going on and off, L1 and L2 (at 480V) could end up using current from the grid- then where does L3 go?

To the grid. And/or somehow to another load connected to L3 directly or inductively through a transformer.

This is pasted from page 2 of the link. If N is required, how can you get 480V, when you only get 480V by not using the N?
The voltage on the low-voltage side must be 3 x 277 V/480 V. A neutral point is required and must lead outward as a neutral conductor.
http://files.sma.de/dl/7418/STP24-US_MV_Trafo-TI-en-10.pdf

Line-to-line voltages are 480. Line-to-neutral voltages are 277. Getting 480V by not connecting to neutral does not mean neutral does not exist. Maybe if you had ever done any electrical work this wouldn't be so hard for you to understand.

 

[PVfarmer]

The powers that be reserve the right to charge ya if things aren't up to "specs".

Not sure if this pic will post.
I think it worked.
According to the grid people, either wye or delta is ok, but according to SMA, if you wanted to interconnect to the grid LV/delta and MV/wye (the right pic), you'd have to use a wye to delta xfmr setup before the delta to wye pictured on the right here.
And the one on the left is what SMA recommends (they recommend that left wye to delta *or* wye to wye (not pictured), but the right one is the "not recommended" by SMA setup).

 

[jaggedben]

To me "must lead outward" is a statement that any wye center point must not be isolated but must ultimately connect to a service or supply neutral. (That is, outward means away from the inverter connection point.)

Yeah. I think perhaps all they mean to clarify is that there must actually be a neutral conductor(s) connecting the neutral point of the transformer to the inverters. You can't use a Y transformer without actually using the neutral. One would think this is obvious but maybe people have been confused.

One thing that is not clear from this is whether they would allow connection of the inverter to an SDS, where the wye point is grounded but not connected directly to POCO neutral.
My gut reaction is that this would be allowed, but that an ungrounded wye source would not be. Nor would a connection to a grounded wye be allowed where only the three hot conductors from the source are present, even if a locally derived neutral is provided via a zig-zag transformer.

The distinction actually makes sense when POCO uses a grounded wye secondary but does not run a neutral.
NEC requires a neutral when line to neutral loads are present, but the GTI is not a load.

All of their examples have the neutral grounded on the side that connects to the inverters, but some of the examples have either ungrouded delta or ungrounded wye on the other side.

 

[jaggedben]

Not sure if this pic will post.
And the one on the left is what SMA requires (they recommend that left wye to delta *or* wye to wye (not pictured), but the right one is the "not recommended" by SMA setup).

Fixed that for you. Tripowers require a wye system so the one on the right would be for some other brand of inverter. Or maybe the 60kW Tripower, as you pointed out.

 

[ggunn]

The powers that be reserve the right to charge ya if things aren't up to "specs".

1. Customer generation connected to the distribution system can cause a variety of system
impacts including steady state and transient voltage changes, harmonic distortion, and
increased fault current levels. Parallel generation systems, which located individually on
higher capacity feeders may not cause very serious impacts, can, on weaker circuits, in
aggregation or in special cases (such as lightly loaded networks), significantly impact the
Company’s Distribution EPS.
2. An Impact Study and a Detailed Study in some cases is needed to identify the severity of
system impacts and the upgrades needed to avoid problems on the Company Distribution
EPS. Typically, an Impact or Detailed Study will be performed by the utility to determine if
the proposed generation on the circuit results in any relay coordination, fault current, and/or
voltage regulation problems.
3. There is a wide range of potential issues associated with the interconnection of DG facilities
to the Company Distribution EPS including, but not limited to:
• Impact on step voltage regulation equipment
• Increased fault duty on Company circuit breakers
• Interference with the operation of protection systems
• Harmonic distortion contributions
• Voltage flicker
• Ground fault overvoltages
• Islanding
• System restoration
• Power system stability
• System reinforcement
• Metering
4. It is important to scrutinize the interconnection of Customer DG facilities to the Company
Distribution EPS so that any negative impacts can be avoided and assure that the customer
generation will have only a positive or, at least, neutral impact on the EPS performance. It is
the intent of any Company study in accordance with SCDG requirements when applicable to
avoid negative power system impacts by identifying the particular type of impact that will
occur and determining the required equipment upgrades that can be installed to mitigate the
issue(s)

And your point is... what?

With an unbalanced load connected to the grid when there is an inverter present and when you are loading up the A and B phases with nothing on the C phase, the inverter feeds the C phase of the service more than the A and B phases. NBD. The inverter does not know or care whether the power it is producing on each phase is being used locally or by the grid.