Transformer sizing for step up and step down transformers

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ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
I ws just saying it is possible and it is

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I know what you are saying (that you can land a three phase inverter on a single phase service) and it isn't. Just saying it is over and over doesn't prove a thing. Provide the complete technical details and I'll look at them, and if you are correct I will stand corrected, admit my error, and issue a public apology to you for doubting you. Otherwise what you are saying is just so much noise.
 

zman990

Member
Location
US
I don't need any feedback at this time I have a manufacturer quoting what solar edge told them I need I will have it next week

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kwired

Electron manager
Location
NE Nebraska
I ws just saying it is possible and it is

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Anything is possible, someone just needs to build it. What you want to do isn't typically available in standardized units and you may want to look harder at what it will actually take to do what you want to do from what several are saying. I am not all that knowledgeable about the PV side of things, but when it comes to general power transformers I know you will not find a unit that takes three phase in, at a certain kVA, and puts that same full kVA out as single phase. If that is not what you are trying to do then I may have been wrong a long time ago, but this has been my understanding from early on in this thread of what you want to do.
 
This might explain why you aren't getting quality feedback from the tech service department. Garbage in = garbage out.
Transformers are possible. We use them all the time. Was that it?
Oh snap! Right on however. If we don't know what he's trying to do, how does the SE guy that said "get this xfmr" know what he's doing?

zman990
I don't need any feedback at this time I have a manufacturer quoting what solar edge told them I need I will have it next week

Ok, now I'm seriously worried, and I'm the guy with the least credentials!
Seriously, dude- does this SE/SolarEdge person know that your *SERVICE* is 120/240V 1ph and not just a little bit of loads, like under 10kW of 120/240V loads?
The only way I can see a 75kVA 480V delta ---> 120/240V center tapped xfmr working for anything you're talking about is off of a 480/277V panel.
As in 480/277V panel ---> your xfmr ---> loads.
Which would mean you'd *have to* have 480/277V service.

You have three big problems:
1. You are talking about 66kW of PV output. That's also 66kVA. You have 120/240V service, possibly 416 amps of 120V (50kVA). Ok. Look--->66,000 / 120V = 550 amps. You can't put 550A thru your 416A service transformer. You don't pwn it!!

2. You are talking about 3 phase inverters that say MEDIUM VOLTAGE XFMR REQUIRED in their installation manual- 120/240V 1ph is not MV!

3. You haven't talked to your POCO! If you did, they'd tell you that you have the wrong service AND the wrong xfmr for your inverters!

Let's review those...

1. Your service is too low of a kVA for your inverters.
2. Your inverters are the wrong phase for your service.
3. It won't work! :happyyes:

Even if you wanted to use 6 of the 11.4kW 1ph SE inverters, or 68.4kW/kVA at 120/240V, your POCO would still say you have to get a single 75kVA service transformer instead of the 50kVA one you have now.
 

jaggedben

Senior Member
Location
Northern California
Occupation
Solar and Energy Storage Installer
I don't need any feedback at this time I have a manufacturer quoting what solar edge told them I need I will have it next week

Dude...
They think you have a high-leg delta service. You've told us it's a single phase service. I hope one of you is wrong. :slaphead:

Good luck.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
What they said. Someone is very much mistaken and I don't think it is I, unless your service is actually three phase. If your system is truly 240/120V single phase and you have ordered a three phase inverter, I hope whoever you bought it from will let you return it because there's no way you are connecting it to the service.

Here's another thing: Looking at the specs for the Solar Edge three phase inverters, the SE9KUS is only 208/120V three phase compatible and the SE10KUS and SE20KUS are only 480/277V three phase compatible. None of them are 240 three phase compatible, so even if you have a three phase 240V service you'll need a transformer.
 
Three Phase Inverter:

5kW, 7kW, 8kW, 9kW, 10kW, 12.5kW, 15kW, 16kW, 17kW, 25kW, 27.6kW, 33.3kW*


* 33.3kW - For medium voltage only - requires medium voltage transformer
http://www.solaredge.us/groups/products/pv-inverter

You said you're using two of the 33.3kW.
You have to have a service xfmr which is MV on the grid side and 480Y/277V on the PV inverter side.
That means it *has* to be a 480/277V service, not the 120/240V one that you have.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Three Phase Inverter:

5kW, 7kW, 8kW, 9kW, 10kW, 12.5kW, 15kW, 16kW, 17kW, 25kW, 27.6kW, 33.3kW*


* 33.3kW - For medium voltage only - requires medium voltage transformer
http://www.solaredge.us/groups/products/pv-inverter

You said you're using two of the 33.3kW.
You have to have a service xfmr which is MV on the grid side and 480Y/277V on the PV inverter side.
That means it *has* to be a 480/277V service, not the 120/240V one that you have.

There are indeed more three phase inverters for standard service interconnection than my old data sheet shows.

SE three phase inverters for 208/120: http://www.solaredge.us/files/pdfs/products/inverters/se-three-phase-us-inverter-208V-datasheet.pdf

Two of them - 9kW and 14.4kW.

SE three phase inverters for 480/277: http://www.solaredge.us/files/pdfs/products/inverters/se-three-phase-us-inverter-datasheet.pdf

Three of them - 10kW, 20kW and 33.3kW. There is nothing on there that says the 33.3kW is different from the other two 480V inverters in terms of connectivity. The output voltage ranges are the same for all three of them.
 
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zman990

Member
Location
US
Anything is possible, someone just needs to build it. What you want to do isn't typically available in standardized units and you may want to look harder at what it will actually take to do what you want to do from what several are saying. I am not all that knowledgeable about the PV side of things, but when it comes to general power transformers I know you will not find a unit that takes three phase in, at a certain kVA, and puts that same full kVA out as single phase. If that is not what you are trying to do then I may have been wrong a long time ago, but this has been my understanding from early on in this thread of what you want to do.
Solar edge asked told me I need a 120/240 primary and 480/277 secondary so that is what is being quoted by a manufacturer that told me they can make anything.
So price is number one concern will it be cheaper if so I may be on to something if not it was fun and has a chance of being the best way of installing larger ground mounts on single phase services idk we see

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zman990

Member
Location
US
Oh snap! Right on however. If we don't know what he's trying to do, how does the SE guy that said "get this xfmr" know what he's doing?



Ok, now I'm seriously worried, and I'm the guy with the least credentials!
Seriously, dude- does this SE/SolarEdge person know that your *SERVICE* is 120/240V 1ph and not just a little bit of loads, like under 10kW of 120/240V loads?
The only way I can see a 75kVA 480V delta ---> 120/240V center tapped xfmr working for anything you're talking about is off of a 480/277V panel.
As in 480/277V panel ---> your xfmr ---> loads.
Which would mean you'd *have to* have 480/277V service.

You have three big problems:
1. You are talking about 66kW of PV output. That's also 66kVA. You have 120/240V service, possibly 416 amps of 120V (50kVA). Ok. Look--->66,000 / 120V = 550 amps. You can't put 550A thru your 416A service transformer. You don't pwn it!!

2. You are talking about 3 phase inverters that say MEDIUM VOLTAGE XFMR REQUIRED in their installation manual- 120/240V 1ph is not MV!

3. You haven't talked to your POCO! If you did, they'd tell you that you have the wrong service AND the wrong xfmr for your inverters!

Let's review those...

1. Your service is too low of a kVA for your inverters.
2. Your inverters are the wrong phase for your service.
3. It won't work! :happyyes:

Even if you wanted to use 6 of the 11.4kW 1ph SE inverters, or 68.4kW/kVA at 120/240V, your POCO would still say you have to get a single 75kVA service transformer instead of the 50kVA one you have now.
Ok so 6*11.4 se inverters is 6*60=360 amps single phase so tap conductors line side fuse at 400 all good not my problem if utility has transformer issues not associated with cost of installing

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zman990

Member
Location
US
Ladies and gentlemen it can someone explain nominal operating voltage in data sheet for solar edge

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Solar edge asked told me I need a 120/240 primary and 480/277 secondary so that is what is being quoted by a manufacturer that told me they can make anything.
So price is number one concern will it be cheaper if so I may be on to something if not it was fun and has a chance of being the best way of installing larger ground mounts on single phase services idk we see

Ok so 6*11.4 se inverters is 6*60=360 amps single phase

Ladies and gentlemen it can someone explain nominal operating voltage in data sheet for solar edge

Just because they can make anything, that doesn't mean it's the right thing!
If the low price is for the wrong thing, that's no good!
I understand (sort of) your intentions. You want to install 60-something kW/KVA of PV inverters on a 120/240V service.

WHICH ONES???

You keep talking about how you're using the SE 33.3kW models, and now you're talking about six 11.4 120/240V SE inverters- but you've got the amps wrong for the 1ph models!

The 11.4kW 120/240V SE 1ph inverter puts out 47.5 amps at its' nominal voltage, the nominal V being 240V- that's 95 amps at 120V.
95 * 6 = 570 amps!!
You only have 400 amps of 120V service- but like I said before, check on that, you might actually only have a 400A main breaker on a 200 amp 120V service.

But also like I said- 1 ph or 3ph doesn't matter here- you CAN'T put 66+kVA of anything thru a 50kVA xfmr.
Here are the specs- the 33W 3ph has 40A of output at 480 WYE (not delta)

40A * 480V * 1.73= 33,216w. Also = to 33.2kW and 33.2 kVA.
33.2kVA = 277 amps at 120V.

So even if there IS some magical way to turn the 3ph inverters output into 120/240V 1ph, you only have room for 1 of them.

But the 3ph SE inverters have a NEUTRAL output which you must use.

Please- tell me- where are you going to attach the N wire coming from the inverter(s)?
A 480V delta 3ph xfmr has no place to attach the N wire...so where will you connect it?

1 phase:
http://www.civicsolar.com/sites/default/files/documents/solaredge-single-phase-datasheet-276766.pdf

3 phase:
AC Output Line Connections 4-wire WYE (L1-L2-L3-N) plus PE
http://www.enfsolar.com/ApolloF/solar/Product/pdf/Inverter/55ed454087d4a.pdf
 
Ladies and gentlemen it can someone explain nominal operating voltage in data sheet for solar edge

Ok, this is where it gets confusing- anyone else want to chip in here?
How can the inverter put out 480V L-L when the neutral is required for reference?
It *would* put out 480V L-L, sure, but that doesn't mean you're supposed to connect it L-L? If you have to use the N wire, the Ls are 277V, correct?

Doesn't zman have to connect the 3 Ls and the N to a 277V 3ph xfmr primary, as well as a some voltage of 3ph secondary to run the xfmr at full kVA?
As a few people have mentioned already?

SE 33.3kW-
AC Output Voltage Minimum-Nominal-Maximum(2) (L-N) 244-277-305 Vac
AC Output Voltage Minimum-Nominal-Maximum(2) (L-L) 422.5-480-529 Vac

Normal Operation
During normal operation the array ground reference is established by the center grounded Wye grid and referenced through the non-isolated inverter. This equivalent protection prevents over voltages on conductors and equipment and, results in the ungrounded array voltage being centered equally on either side of ground.
http://www.solaredge.com/files/pdfs/se_3p_system_design_and_nec.pdf
 

kwired

Electron manager
Location
NE Nebraska
Solar edge asked told me I need a 120/240 primary and 480/277 secondary so that is what is being quoted by a manufacturer that told me they can make anything.

I think most of us are asking (for your best interest) that you confirm that it is indeed 120/240 single phase that they are going to send you, as most are betting there is a misunderstanding and they intend to send you a 120/240 delta three phase unit.

This is a basic misapplication of transformers in general before you even get into some of the more technical reasons why it might not work.

Forget the PV for a moment, there is no such transformer that will take 120/240 single phase in and output 480/277 three phase, there are phase converters, VFD's or other units that use a combination of other basic components that can do this - but none of them can be "reverse fed" to convert three phase to single phase.
 
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