480/277 WYE service to 120/240 Single phase

[PVfarmer]

Dude, read what I said again. This time I'll bold the important parts for you.
1. "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,"

2. 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.

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

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

5. 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.

1. Yes. But is it really either/or as far as utility/separately derived? You could connect to either just the utility, or utility *and* a separately derived, while you can't connect to separately derived only-
And when you are connecting output from PV inverter(s) to both utility and SD, those systems should logically be the same voltage.

2. The OP says "I figured 480 delta to 240 delta would work. I am wondering if i connect the A and C phase to a single phase panel and just leave the High leg out." 4

480 delta won't work, because the system is 480/277V wye, unless you go 480/277 wye to 480 delta and then (with a 2nd xfmr) 480 delta to XXXV like SMA says as a "fix" for LV delta on pages 6 and 7.
And connecting to A and C (or L1 and L2 as I said) to supply a load either won't work at all or isn't the best way to do it.
The OP would want to use A, B, C, and N (or L1, L2, L3, and N) for the load.

3. It sure isn't encouraged!

4. How about this- say the OP has just one Tripower, a 15000TL/15000 watt. Say the load is a 20hp irrigation pump instead of a welder and lights. 20hp= 14920 watts.
The OP could:

A- Use a 3 phase 480V irrigation pump. That would draw all 18 amps the 15000TL puts out at max. So when the 15000TL is running at 50%, the rest would come from the grid.
B- Use a 1 phase 240V pump, from L1 and L2 of grid/inverter into a 480V to 240V xfmr. That would draw 62.5 amps, but that isn't possible from 2 legs of the 15000TL- you only get 12A from 2 legs, which is 41.5 amps @ 240V.

A seems "workable" and B does not- with B, there would have to be current going both to and from the grid. That sounds wrong to me.

5. I do understand it- the neutral still has to go somewhere, which is to ground. I just don't think to ground qualifies as "leading out"...

 

[PVfarmer]

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.

Point being, I think the grid people would come back with a "no" if you said you wanted to connect their 480/277V wye system (which is also getting 3 phases of 277V L-N from inverters) to a 480 delta >> 240 delta xfmr.
With a small load, they might say "connect a leg of 277 L-N to a single phase xfmr".
And if the load was a fairly large 240V one, they might say "please use 3 single phase 277V >> 240V xfmrs and wire them delta on the 240V side".

the inverter feeds the C phase of the service more than the A and B phases.
What if the output of the inverter is less than the load?
Say the grid side is connected at 12.47kV delta and the service is 480/277V wye, 100A like the OP's.
That could be done with three single phase 12.47kv > 277V xfmrs (30kVA each), wired in delta on the MV/12.47 side and wye on 480/277 LV side.
Or it could be done with one 3 phase 12.4kV delta to 480/277 wye xfmr, they don't make 90kVA so you'd use a 112.5kVA.
Either way- if the load is say 12kW on the A and B phases, and the inverter is only putting out 10kW at that moment, or 3.33A each on phases A B and C, how can you use 6.66kW from the inverter phases A and B towards the load while getting the remaining 5.3kW from the grid....AND put the 3.33kW from phase C into the grid?

 

[electrofelon]

Point being, I think the grid people would come back with a "no" if you said you wanted to connect their 480/277V wye system (which is also getting 3 phases of 277V L-N from inverters) to a 480 delta >> 240 delta xfmr.
With a small load, they might say "connect a leg of 277 L-N to a single phase xfmr".
And if the load was a fairly large 240V one, they might say "please use 3 single phase 277V >> 240V xfmrs and wire them delta on the 240V side".

the inverter feeds the C phase of the service more than the A and B phases.
What if the output of the inverter is less than the load?
Say the grid side is connected at 12.47kV delta and the service is 480/277V wye, 100A like the OP's.
That could be done with three single phase 12.47kv > 277V xfmrs (30kVA each), wired in delta on the MV/12.47 side and wye on 480/277 LV side.
Or it could be done with one 3 phase 12.4kV delta to 480/277 wye xfmr, they don't make 90kVA so you'd use a 112.5kVA.
Either way- if the load is say 12kW on the A and B phases, and the inverter is only putting out 10kW at that moment, or 3.33A each on phases A B and C, how can you use 6.66kW from the inverter phases A and B towards the load while getting the remaining 5.3kW from the grid....AND put the 3.33kW from phase C into the grid?

If I am correctly understanding what you are proposing/contemplating, you can certainly have the net energy flow on one phase going one way and the other two phases going the other way - Why not? Regarding balancing from a utility standpoint, I have never ever heard of a customer who got scolded by their utility for poor balancing across the 3 phases. I dont think the watthour meter even keeps track of that (I have used utility data in lieu of load calcs several times and the spreadsheet had a bunch of fields but none broke down current per phase).

 

[ggunn]

1. Yes. But is it really either/or as far as utility/separately derived? You could connect to either just the utility, or utility *and* a separately derived, while you can't connect to separately derived only-
And when you are connecting output from PV inverter(s) to both utility and SD, those systems should logically be the same voltage.

2. The OP says "I figured 480 delta to 240 delta would work. I am wondering if i connect the A and C phase to a single phase panel and just leave the High leg out." 4

480 delta won't work, because the system is 480/277V wye, unless you go 480/277 wye to 480 delta and then (with a 2nd xfmr) 480 delta to XXXV like SMA says as a "fix" for LV delta on pages 6 and 7.
And connecting to A and C (or L1 and L2 as I said) to supply a load either won't work at all or isn't the best way to do it.
The OP would want to use A, B, C, and N (or L1, L2, L3, and N) for the load.

3. It sure isn't encouraged!

4. How about this- say the OP has just one Tripower, a 15000TL/15000 watt. Say the load is a 20hp irrigation pump instead of a welder and lights. 20hp= 14920 watts.
The OP could:

A- Use a 3 phase 480V irrigation pump. That would draw all 18 amps the 15000TL puts out at max. So when the 15000TL is running at 50%, the rest would come from the grid.
B- Use a 1 phase 240V pump, from L1 and L2 of grid/inverter into a 480V to 240V xfmr. That would draw 62.5 amps, but that isn't possible from 2 legs of the 15000TL- you only get 12A from 2 legs, which is 41.5 amps @ 240V.

A seems "workable" and B does not- with B, there would have to be current going both to and from the grid. That sounds wrong to me.

5. I do understand it- the neutral still has to go somewhere, which is to ground. I just don't think to ground qualifies as "leading out"...

Why are you even worried about the load? The amount of imbalance on the service is the same whether there is an inverter on line or not.

So, why is it that he couldn't just connect the inverter to the 240 delta service through a 480/277 wye to 240 delta transformer? I have done it with a 480/277 inverter bank to a 208 service without pulling a neutral from the service, and tying the neutral to ground on the 480 side of the transformer. It worked (and still is working) just fine.

 

[PVfarmer]

Why are you even worried about the load? The amount of imbalance on the service is the same whether there is an inverter on line or not.

So, why is it that he couldn't just connect the inverter to the 240 delta service through a 480/277 wye to 240 delta transformer? I have done it with a 480/277 inverter bank to a 208 service without pulling a neutral from the service, and tying the neutral to ground on the 480 side of the transformer. It worked (and still is working) just fine.

Don't you mean 240V delta LOAD there? His service is already 480/277 wye.
I see a lot to 480 delta to 240 delta xfmrs, and 240 delta to 480/277 xfmrs, but a 3 phase 480/277 to 240 delta doesn't seem common.
Of course with a bank of 3 single phase you can do 480/277 to 240 delta easily- the 480/277 side is wired 277V L-N.

Because when you "tie the N to ground" on the 480 side, you mean of the 480/277 wye xfmr, that's L to N and also N to ground- because the N of the xfmr is linked to L1 L2 and L3, it's 3 phases of 277V.

I have done it with a 480/277 inverter bank to a 208 service

You mean 208/120 wye service, right? So the step-down xfmrs are taking in 3 phases of 277V wye from the inverters and putting out 120V L-N and 208V L-L, correct?

I guess he *could* really use three 1 phase 277 xfmrs going from 277V L-N wye on the inverter side to:
208Y or
240 delta or
120/240 single phase.
But if you go 240 delta and tap between 2 legs to get 120V, you have that unusable wild leg, which...may be not the best setup.

 

[jaggedben]

1. Yes. But is it really either/or as far as utility/separately derived?

Yes, it really is either/or because that's how a separately derived system is defined and an inverter can only connect to one system. You clearly don't understand what a separately derived system is. You should look that up.

while you can't connect to separately derived only-

Yes you can. The examples with two transformers in the SMA document are exactly that.

5. I do understand it- the neutral still has to go somewhere, which is to ground. I just don't think to ground qualifies as "leading out"...

The neutral has to connect to the inverter. Judging by the examples, SMA also wants it grounded. These are not mutually exclusive. I still don't think you understand.

I'm only responding to try to make sure misinformation is corrected. The rest of your post demonstrates mostly lack of reading comprehension and I'll trust that other readers can figure that out.

 

[PVfarmer]

you can certainly have the net energy flow on one phase going one way and the other two phases going the other way - Why not?

If you've got a MV delta and LV wye setup, a load drawn from A and B phases on the lower lines is coming from the upper A B and C lines- so how could you feed into the grid from phase C of the lower lines while feeding from the grid to the load from A B and C above?
The lower C phase would be going out to A and C phases on the top lines here- are you saying it'll then go back to the load through the left and middle xfmrs?
If so, that can't be the best way to do it.
This diagram is just a quickie, but it's sort of a Tripower with only phases A and B going to a load.

 

[PVfarmer]

1/Yes, it really is either/or because that's how a separately derived system is defined and an inverter can only connect to one system. You clearly don't understand what a separately derived system is. You should look that up.

2. while you can't connect to separately derived only-
Yes you can. The examples with two transformers in the SMA document are exactly that.

3. The neutral has to connect to the inverter. Judging by the examples, SMA also wants it grounded. These are not mutually exclusive. I still don't think you understand.

1. If you have 480/277 inverter(s) connected line-side to a 480/277 service, and those 3 phases of 277V are connected to xfmrs that supply a 208/120 load to simplfy things, that load is separately derived, so the inverter(s) are connected to both systems, not either/or.
. By definition, a separately derived system is a “premises wiring system whose power is derived from a battery, a solar photovoltaic system, or from a generator, transformer, or converter windings, and that has no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system.” While each year brings more advances in solar photovoltaic and battery system technologies, clearly, transformers remain the most common power source for separately derived systems. Typically, for example, in a high-rise building, power will be distributed at the 480-volt level. The 480/277 voltages can be used for power applications. At intermediate floors, 480Y/277-volt transformers are installed to transform a 480-volt supply to a 208Y/120-volt system for lighting, convenience receptacles, and appliance loads.
http://www.ecmag.com/section/codes-standards/grounding-separately-derived-systems-part-1-basics

2. By connecting to a separately derived only I meant not connecting to the grid- Tripowers can't do that.

3. I think they want it both leading out and grounded. The neutral(s) from the inverter(s) has/have to connect to the xfmr(s) before going to ground is the way I'm reading it.

 

[jaggedben]

1. If you have 480/277 inverter(s) connected line-side to a 480/277 service, and those 3 phases of 277V are connected to xfmrs that supply a 208/120 load to simplfy things, that load is separately derived, so the inverter(s) are connected to both systems, not either/or.

No, the inverter is only connected to the service in that case. Look at your own quote.

. By definition, a separately derived system is a “premises wiring system whose power is derived from a battery, a solar photovoltaic system, or from a generator, transformer, or converter windings, and that has no direct electrical connection, including a solidly connected grounded circuit conductor, to supply conductors originating in another system.”

When I say 'connected' here I don't mean inductively linked through a transformer. Let's distinguish between a direct electrical connection and connection inductively through a transformer. A tripower can be connected to any number of systems by induction, but only one by direct electrical connection. Does that help?
:slaphead:

2. By connecting to a separately derived only I meant not connecting to the grid- Tripowers can't do that.

Sure they can. They can connect to any 480/277 system that sets voltage and frequency and can absorb their output. As mentioned earlier though, they're not designed for systems that aren't powered from the grid.

3. I think they want it both leading out and grounded. The neutral(s) from the inverter(s) has/have to connect to the xfmr(s) before going to ground is the way I'm reading it.

The transformer will probably have two terminals connected to the neutral point, one for the neutral conductor and the other for the ground conductor. If not, you just connect the ground wire to the neutral wire close by. That's what it means to ground a conductor.

 

[jaggedben]

The lower C phase would be going out to A and C phases on the top lines here- are you saying it'll then go back to the load through the left and middle xfmrs?
If so, that can't be the best way to do it.

The power will flow from the inverter to the load on the phases where there's load, and from the inverter to the grid on the phases where there's no load.
There's absolutely nothing wrong with it. It's how all grid-tied inverters work. It's kind of the whole point of this solar thing we're doing.

 

[PVfarmer]

1. No, the inverter is only connected to the service in that case. Look at your own quote.
2. When I say 'connected' here I don't mean inductively linked through a transformer. Let's distinguish between a direct electrical connection and connection inductively through a transformer. A tripower can be connected to any number of systems by induction, but only one by direct electrical connection. Does that help?
:slaphead:

3. Sure they can. They can connect to any 480/277 system that sets voltage and frequency and can absorb their output. As mentioned earlier though, they're not designed for systems that aren't powered from the grid.

4. The transformer will probably have two terminals connected to the neutral point, one for the neutral conductor and the other for the ground conductor. If not, you just connect the ground wire to the neutral wire close by. That's what it means to ground a conductor.

Originally Posted by PVfarmer

The lower C phase would be going out to A and C phases on the top lines here- are you saying it'll then go back to the load through the left and middle xfmrs?
If so, that can't be the best way to do it.
That's exactly right, and absolutely the best way to do it.

I really don't get that- how is taking the C phase of 277V, stepping it up to the A and C phases of 12.47kV grid, then back down to A and B phases of 277V for the load better than just using 277V A B and C for the load *and* the grid interconnect?

1. Sure, the inverter is direct connected to the 480/277V service electrically, and OK, it's not connected to the separate system directly- but it is connected to the xfmr(s) that supply that system. So it's connected to the 480/277V service and they are both supplying the load- I guess I was using connected when I meant supplying there then.

2. I think so.

3. They can connect to any 480/277 system that sets voltage and frequency and can absorb their output.
But the inverter output would be say 15000 watts at high noon and maybe 3000 watts at 6PM in summer - not sure what kind of system would work that way/have that load profile.

Say you had that single 15000TL and wanted to use it off grid- you'd have to get a 43.2kWh or 57.6kWH battery bank and maybe 2 Outback Radian 8048A hybrid inverters- then you could take the 480/277 from the 15000TL, and run it through xfmrs down to 120/240V into either the AC generator inputs or the "grid tie" inputs of the Radians-(might as well use the grid input if you are off-grid- then the PV system is acting as the grid) anyway both inputs can take 50A each, and the 18.1A output at 480/277 from the inverter would be 62.5A at 240V, so 31.25A into each Radian, no problem.

4. The output of the Tripowers is L1 L2 L3 and N, and there's also a PE/ground connection wire, which isn't direct connected electrically to the other 4. I'm pretty sure some (not all) of the xfmr wiring diagrams I've seen have say H1 H2 H3 and N connection points and then a solid dot to the side which I believe is the same sort of ground wire, not connected electrically.
Or single phase xfmr diagrams will have H1 H2 and the unconnected dot- if you connect H1 to the inverter's L1 and H2 to the inverter's N, there's your neutral leading out, and then you'd also wire that N to the xfmr to ground connection like you mentioned.

 

[jaggedben]

I really don't get that- how is taking the C phase of 277V, stepping it up to the A and C phases of 12.47kV grid, then back down to A and B phases of 277V for the load better than just using 277V A B and C for the load *and* the grid interconnect?

You're not stepping it up and back down. Power flows first to the local loads and then to the grid, on each phase.

But the inverter output would be say 15000 watts at high noon and maybe 3000 watts at 6PM in summer - not sure what kind of system would work that way/have that load profile.

The grid has a large enough load that other generators can be managed to fit its load profile around what's supplied by all the solar connected to it. There are limits to this flexibility, of course, but with the possible exception of Hawaii we haven't gotten anywhere near them in the US. Germany is a different story.

 

[PVfarmer]

You're not stepping it up and back down. Power flows first to the local loads and then to the grid, on each phase.

The grid has a large enough load that other generators can be managed to fit its load profile around what's supplied by all the solar connected to it. There are limits to this flexibility, of course, but with the possible exception of Hawaii we haven't gotten anywhere near them in the US. Germany is a different story.

Originally Posted by electrofelon

you can certainly have the net energy flow on one phase going one way and the other two phases going the other way - Why not?

Thanks for hanging in here- I still don't get it.
If you have power flowing to the loads on A and B in this diagram, because the load is only wired to A and B:
http://forums.mikeholt.com/showthread.php?t=171944&p=1678225#post1678225

How can the inverter power/phase C stay on the LV side and "get to" the load on A and B?
The inverter would have to leave phase C "empty" and put those amps onto phases A and B only- but I don't think they do that.

I don't know about that second part- if you look at page 75 here, DG systems <100kW are "triggering large studies (in New England) due to aggregate generation".
http://www.nationalgridus.com/non_html/ri_dg_seminar.pdf

 

[wwhitney]

How can the inverter power/phase C stay on the LV side and "get to" the load on A and B?

It won't. It will go out to the grid and power somebody else's load on the C phase. If there's another customer on the same POCO transformer, it may do this by staying on the LV side. Otherwise, it will go through a couple POCO transformers first.

Cheers, Wayne

 

[PVfarmer]

It won't. It will go out to the grid and power somebody else's load on the C phase.

Howdy, Wayne....I'm still confused- when the phase C of the inverter is going out to grid through the xfmr on the right (call it Z), which is connected to A and C phases grid-side, why wouldn't it go back to the load through the left xfmr (call it X) and the middle xfmr (call it Y).
The grid phase A is connected to xfmr X and grid phase C is connected to xfmr Y, so wouldn't it stay on the LV

If there's another customer on the same POCO transformer, it may do this by staying on the LV side.

So if inverter phase C is only connected to xfmr Z, there would have to be another meter there for the other customer- then the inverter phase C would go to that 2nd customer load while A and B from inverter are going to customer 1. Right?:?

 

[jaggedben]

So if inverter phase C is only connected to xfmr Z, there would have to be another meter there for the other customer- then the inverter phase C would go to that 2nd customer load while A and B from inverter are going to customer 1. Right?:?

You're finally catching on.

 

[PVfarmer]

Originally Posted by PVfarmer

So if inverter phase C is only connected to xfmr Z, there would have to be another meter there for the other customer- then the inverter phase C would go to that 2nd customer load while A and B from inverter are going to customer 1. Right?:?

You're finally catching on.

Ok, but then what happens if there is no "other customer" load on phase C during daylight hours?
Inverter phase C goes to the step-up to grid xfmr.
I don't get why you'd want to have a PV system, but only connect 2 phases of it to the load instead of three- you'd be taking/paying for power from the grid 33% more of the time by only using 2 phases of the inverter(s).
Depending on the load of course- if it was small, maybe wouldn't matter so much, like the OP's 40A 240V welder, 9600 watts = 11.6A at 480/277V, so that's 27.5% of the 42.2A (3 phase) that the OP's 2 inverters are putting out at maximum.

That means the one phase of the inverter would only be supplying the welder 100% around midday.
If he used all three phases from the inverters, the PV would be running the welder 100% until total output dropped below 27.5%.

This is a farm we're talking about here- farmers in general are not into paying more for something (grid power) when they can get it for less (PV Power)

 

[wwhitney]

So how does a 3 phase meter work? Will it just record the net power produced or consumed, so that the imbalance doesn't matter?

Cheers, Wayne

 

[PVfarmer]

So how does a 3 phase meter work? Will it just record the net power produced or consumed, so that the imbalance doesn't matter?

Cheers, Wayne

I think a basic old-school one won't, but I'm not sure.
Now I'm wondering- if the "other customer" you spoke of has loads with no generation- the meter for that customer wouldn't know if the power was coming from PV or grid or both- so the POCO would be charging the 2nd customer for customer 1's PV output- how would customer 1 get paid?

This one will record net.
Another reason is that this meter will report the direction of current on each line in real-time so you can determine the net watts (forward or reverse) at any time.
http://www.ekmmetering.com/ekm-omni...ay-controlling-universal-smart-kwh-meter.html

I was wondering the same thing for 3 phase myself, after looking at this.
http://www.outbackpower.com/downloads/documents/wiring_diagram/Single_Radian_net-meter_drawing.pdf

And this is sort of interesting- there's some controversy Down Under.
I have never seen an installation where this happens. All the 3 phase meters that I have seen take into account the sum of all the electricity being used on all the phases and then subtract that from the amount of solar energy being generated to calculate the import or export amount for billing. i.e. if you are on a stingy FiT, they don’t penalise you financially for having a single phase inverter on a 3 phase supply.
http://www.solarquotes.com.au/blog/...bout-connecting-solar-to-your-3-phase-supply/

 

[GoldDigger]

Originally Posted by PVfarmer

So if inverter phase C is only connected to xfmr Z, there would have to be another meter there for the other customer- then the inverter phase C would go to that 2nd customer load while A and B from inverter are going to customer 1. Right?:?




Ok, but then what happens if there is no "other customer" load on phase C during daylight hours?
Inverter phase C goes to the step-up to grid xfmr.
I don't get why you'd want to have a PV system, but only connect 2 phases of it to the load instead of three- you'd be taking/paying for power from the grid 33% more of the time by only using 2 phases of the inverter(s).
Depending on the load of course- if it was small, maybe wouldn't matter so much, like the OP's 40A 240V welder, 9600 watts = 11.6A at 480/277V, so that's 27.5% of the 42.2A (3 phase) that the OP's 2 inverters are putting out at maximum.

That means the one phase of the inverter would only be supplying the welder 100% around midday.
If he used all three phases from the inverters, the PV would be running the welder 100% until total output dropped below 27.5%.

This is a farm we're talking about here- farmers in general are not into paying more for something (grid power) when they can get it for less (PV Power)

Ultimately very simple. The generating plant winding (or whatever) for that phase simply sources less current than the windings for the other two legs.

It is less efficient than driving a balanced load in terms of reaching maximum output, but it does not produce (to first order) any energy waste at the generating plant.