Single phase inverter fed from three phase system

[BBGigante]

Hello,

Recently in my worksite we acquired an inverter as back up energy for the offices in case of blackouts (common in my country). The equipment is a TRACE APC6048 Pure Sine Wave inverter which requires 220V input to work properly (according to specs accepts from 194-243V).

The office building is powered from a three phase, Delta-Y 460-208/120V transformer, and what occurred is that when I tried powering the inverter from that 208V three phase system running two lines to the input side of the inverter, the electronics went haywire (I heard a strong rattling sound coming out of the inverter for 2 seconds and then the sound stopped, but the output of the inverter was out of specs, voltage readings were wrong between the L1, L2 and Neutral).

I took the equipment back to the seller and then they told me that it can’t feed it from a three phase system but rather from a single phase system, so I needed to get a special transformer in order to change from 208V line-line voltage from the thee phase transformer to 240V single phase and then input that to the inverter.

• Has anyone here seen any case like it?
• What difference does it makes for the electronics, being powered from 208V three phase and 240V single phase (given the fact that 208V is within the tolerated range)?
• What type of transformer do you think this "special transformer" is? Scott-T? Open Delta? Any other?

Here's a link to a very similar equipment I found:
http://www.extremeheatsolar.co.za/AP-Inverter-owners-Manual-Version-4.0.pdf

Thanks for any reply.

 

[GoldDigger]

The biggest problem with connecting the inverter to two phases and the neutral is that the center tap of a transformer winding from L to L will not be at neutral voltage as it would be with 120/240 single phase. Some parts of the electronics may be relying on that.

We need more info on how you intend to connect it. Will it be trying to drive three phase loads when running as backup? That simply cannot be done, period.

There is a transformer config, not Scott-T, that can feed equally from three phases to single phase, but I am pretty sure it would not help you.

Sent from my XT1585 using Tapatalk

 

[Smart $]

If all you did was power up the inverter with no load connected, then the unit was defective and the seller is feeding you a line of BS.

 

[Smart $]

Here's a link to a very similar equipment I found:
http://www.extremeheatsolar.co.za/AP-Inverter-owners-Manual-Version-4.0.pdf

Similar will not cut it.

Aside from that, this is a DC to AC inverter. Is your inverter also a DC to AC inverter? If yes, what are you powering it with?

Something sounds hinky with this whole setup.

 

[BBGigante]

Wow thank you so much for that quick response.

The inverter is meant to drive a 6KVA UPS (Eaton Powerware 9170+) which uses split phase power modules to produce 220V output, so I have two lines and a neutral coming out of the UPS thus providing me with two 120V circuits to power all the computers and servers. The inverter also powers all the lighting in the building (fluorescent lamps).

Right now I have an old inverter, pretty much like a SW5548 which requires 120V input so I simply take one line and neutral from the three phase transformer and feed it straight forward, then at the output I have a step up transformer to make it 220V. The thing is that inverter is faulty and we need to replace it, but now I ordered this APC6048 which provides a 240V output straight forward without the need of the step up transformer.

I thought I could power it from my three phase system since all my air conditioners are powered from it (220V single phase units) and they run just fine, considering they have an electronic card in the indoor unit to control its operation.

 

[BBGigante]

The upper drawing is what it looked like before, it was working correctly. The lower drawing is what I tried, and failed.

As I said before the first inverter is 120V input, and the output was stepped up via a transformer to feed the UPS and some lighting. The new inverter is 220V input and the output goes straight to the UPS, but I couldn’t get the output to work correctly, I tested with no load connected to it.

 

[Smart $]

The upper drawing is what it looked like before, it was working correctly. The lower drawing is what I tried, and failed....

Too small to read text.

Nevermind. Opened image in new window and zoomed in.

 

[Smart $]

...
As I said before the first inverter is 120V input, and the output was stepped up via a transformer to feed the UPS and some lighting. The new inverter is 220V input and the output goes straight to the UPS, but I couldn’t get the output to work correctly, I tested with no load connected to it.

Why do you not power the lighting and UPS directly without the inverter?

The 120-208V labeled 1Ø transformer is not correct. You cannot power 120V lighting with a 208V secondary.

 

[BBGigante]

I'm sorry my drawing is kind of funky; the lighting circuits are powered from one line of the 208V circuits and the neutral bar on the right, not straight from the 208V lines. What I have is two 120V circuits from those two lines and the neutral.

 

[BBGigante]

The reason for powering the UPS and lighting from the inverter is that when a blackout occurs, the lighting stays on until the generator kicks up, and the UPS because at night the factory is closed and the generators are not working in case of blackouts, so the UPS would discharge and the servers would go off.

 

[Electric-Light]

Hello,

Recently in my worksite we acquired an inverter as back up energy for the offices in case of blackouts (common in my country). The equipment is a TRACE APC6048 Pure Sine Wave inverter which requires 220V input to work properly (according to specs accepts from 194-243V).

The office building is powered from a three phase, Delta-Y 460-208/120V transformer, and what occurred is that when I tried powering the inverter from that 208V three phase system running two lines to the input side of the inverter, the electronics went haywire (I heard a strong rattling sound coming out of the inverter for 2 seconds and then the sound stopped, but the output of the inverter was out of specs, voltage readings were wrong between the L1, L2 and Neutral).

You should read through the equipment manual. See if neutral is required as mentioned already.
What were those voltage readings? It might be usable over the range you provided but might require setting it properly for the line and load voltage.

In your application context inverter and UPS are the same thing and you should avoid the layers of series connected transformers and UPS to minimize efficiency reduction.

I took the equipment back to the seller and then they told me that it can’t feed it from a three phase system but rather from a single phase system, so I needed to get a special transformer in order to change from 208V line-line voltage from the thee phase transformer to 240V single phase and then input that to the inverter.

What difference does it makes for the electronics, being powered from 208V three phase and 240V single phase

They're running single phase 208 or 240v. When you have UPS involved, it affects the line cut off or transfer point.

 

[Smart $]

I'm sorry my drawing is kind of funky; the lighting circuits are powered from one line of the 208V circuits and the neutral bar on the right, not straight from the 208V lines. What I have is two 120V circuits from those two lines and the neutral.

So the transformer secondary is [split phase] 120/240V... not 208V.

And the inverter has a 48VDC battery backup input?

 

[BBGigante]

So the transformer secondary is [split phase] 120/240V... not 208V.

And the inverter has a 48VDC battery backup input?

Well the step up transformer after the old inverter just has four terminals, two inputs (L and N) and two outputs (L1 and L2) so I don’t think it's split phase transformer. What we do is that we take one line of the transformer output and the same neutral that’s used originally at the input of the inverter and that gives you 120V, same for the other line so you have two circuits with the same neutral. If you take a closer look the same neutral goes to the first and second panel.

As for the inverter it does have a 48VDC battery bank so it works when there’s a blackout, that’s the reason of having it. Imagine is the middle of the night and the power goes out, diesel generators don’t start up because they’re turned off, so the UPS would discharge after 20mins approximately. In this case the inverter provides several hours of runtime until the utility power comes back or somebody starts the generators in the morning.

Thank you for sharing with me, I know I’m not an expert but I’m trying to explain things just how they are as close to reality as possible.

 

[Besoeker]

Anyone else have trouble swallowing this?

"Pure sinewave AC with an average THD of 15%"

 

[BBGigante]

You should read through the equipment manual. See if neutral is required as mentioned already.
What were those voltage readings? It might be usable over the range you provided but might require setting it properly for the line and load voltage.

In your application context inverter and UPS are the same thing and you should avoid the layers of series connected transformers and UPS to minimize efficiency reduction.

I took the equipment back to the seller and then they told me that it can’t feed it from a three phase system but rather from a single phase system, so I needed to get a special transformer in order to change from 208V line-line voltage from the thee phase transformer to 240V single phase and then input that to the inverter.

In this case the neutral is required because the UPS requires it in order to provide 120V output, also the lighting circuits before the UPS also require it. About the readings I don’t remember exactly but they were way off, I think the reading was 84V between L1 and N, and 234 between L2 and N, also both readings were fluctuating a Little.
Anyways the supplier confirmed it was damaged and repaired it at their shop, then tested it and readings were ok (they replaced a board inside though didn’t say which exactly) and now we’re waiting for that famous special transformer to arrive.

[/QUOTE]They're running single phase 208 or 240v. When you have UPS involved, it affects the line cut off or transfer point.[/QUOTE]

About this part I was talking about what difference does it makes for the new inverter control board to be fed from a three phase 208V circuit and a single phase 240V circuit. Because in terms of the acceptable input range specified, 208V it’s ok.

 

[BBGigante]

Anyone else have trouble swallowing this?

"Pure sinewave AC with an average THD of 15%"

Well that link I posted is a Chinese one I found online which looks oddly familiar (almost the same) as the equipment I got here, only that mine's branded "TRACE Engineering", but I’m not really quite sure about that because I think TRACE as a brand disappeared a long time ago or was absorbed by XANTREX, can’t really find it on the internet anymore.

Not saying that the one I got is better than this one, maybe it’s the same equipment and they just rebranded it, but just saying that the manual I provided in that link is not for the equipment I received, I just found it online by running a search on “TRACE APC6048”. Maybe that one is just a modified sine wave really.

 

[Smart $]

Well the step up transformer after the old inverter just has four terminals, two inputs (L and N) and two outputs (L1 and L2) so I don’t think it's split phase transformer. What we do is that we take one line of the transformer output and the same neutral that’s used originally at the input of the inverter and that gives you 120V, same for the other line so you have two circuits with the same neutral. If you take a closer look the same neutral goes to the first and second panel.

As for the inverter it does have a 48VDC battery bank so it works when there’s a blackout, that’s the reason of having it. Imagine is the middle of the night and the power goes out, diesel generators don’t start up because they’re turned off, so the UPS would discharge after 20mins approximately. In this case the inverter provides several hours of runtime until the utility power comes back or somebody starts the generators in the morning.

Thank you for sharing with me, I know I’m not an expert but I’m trying to explain things just how they are as close to reality as possible.

Okay.

What it amounts to is you got lucky with the original setup. This is why your new setup has wonky L-N voltages and likely why it let the smoke out (perhaps no actual smoke, but functionally the same). :happyyes:

 

[Smart $]

If you can't find an exact replacement inverter and want to use the one you have, i.e. a replacement, you'll need a transformer with a rated primary voltage the same as the inverter output, with a 120/240V 1Ø 3W secondary. The secondary center tap needs to be grounded to same grounding electrode system as the 480V-208/120V incoming transformer. Do not connect to the same neutral as in your drawing.

However, you should check whether your UPS can tolerate a 240V input voltage.

 

[BBGigante]

If you can't find an exact replacement inverter and want to use the one you have, i.e. a replacement, you'll need a transformer with a rated primary voltage the same as the inverter output, with a 120/240V 1Ø 3W secondary. The secondary center tap needs to be grounded to same grounding electrode system as the 480V-208/120V incoming transformer. Do not connect to the same neutral as in your drawing.

However, you should check whether your UPS can tolerate a 240V input voltage.

Sir that was a very clear response, thank you very much. Tomorrow I’ll be getting that new transformer they recommend to feed my new inverter, so I’ll be setting it up and I’ll let you guys know how it went.

As for the UPS I think it can take it, it is e very versatile equipment with lots of configurations available but I will review that point with the user manual before connecting it.

The one thing I don’t get about the original set up we have there (it’s been like that since I got there) is the neutral point being the same before the inverter and after the step up transformer. Does it means that in my new set up I’ll have to tie all neutrals together? i.e. the system neutral with the new transformer’s output and the new inverter neutral terminal, so when I take one of the inverter’s output lines it is referenced to that same neutral potential and I can use that neutral later on the subsequent sub-panel as a supply for my 120V circuit.

 

[Electric-Light]

In this case the neutral is required because the UPS requires it in order to provide 120V output, also the lighting circuits before the UPS also require it. About the readings I don’t remember exactly but they were way off, I think the reading was 84V between L1 and N, and 234 between L2 and N, also both readings were fluctuating a Little.

Earlier you said:

when I tried powering the inverter from that 208V three phase system running two lines to the input side of the inverter

I don't know how it is designed inside the magic box. If you're saying you energized the equipment without supplying the neutral it requires on the input inside, that is likely what damaged it. You should ask Schneider Electric if that old model can be configured for 120v with a jumper block. Let the new system be your new UPS. Ditch (bypass) the other UPS. Get a copy of the installation manual.

All these transformation back and forth downstream of the UPS (inverter) will cut down the run-time by wasting power.
If it has a separate input for generator power, the normal side should go to a unprotected power and generator side to generator protected power.

About this part I was talking about what difference does it makes for the new inverter control board to be fed from a three phase 208V circuit and a single phase 240V circuit. Because in terms of the acceptable input range specified, 208V it’s ok.

Read the installation instructions. This is equipment specific information that I have no real idea about.