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Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 12:10am 01 Oct 2022
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I have a 32A 3 phase outlet. I want to run single phase loads off 2 of the phases back to neutral. Phase to phase is 415 IF I remember correctly so that won't do for 230V Equipment.
From the limited information I can gather, because of the phase separation and being an unbalanced load, I should be able to run more than the 7300W total load 32A should equate to.
If figure this to be 7300w / .3 = 2400W so total of 9700W rounded off.
Is this correct?
I asked sparky and he said because the neutral carried the load from each phase it worked out at the 7300W but he forgot the science and it was more but couldn't say how much.
The basic question is how much power can I push ( solar inverters) back down each of the 2 individual phases?
I have been running a 4 and a 5KW inverter for some time, one on each phase and had no problem but Sparky seems to think that's ifffy... at the same time he keeps saying he knows nothing about solar, not that I see this has anything to do with solar, just AC Operation.
Godoh Guru Joined: 26/09/2020 Location: AustraliaPosts: 458
Posted: 08:40am 01 Oct 2022
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Davo, I am not sure where you get your figures from. The whole current thing comes down to the power factor of the circuit.
Power in an AC circuit is calculated by Power = 1.732 X V I cos Sorry don't have symbols but 1.732 is the square root of 3 Cos is Cos theta or the power factor of the load.
So a 32 amp three phase socket should be able to supply a total of 23Kw. That is with a power factor of 1 ( purely resistive load).
Each phase should supply 12.748Kw with the same power factor.
The problem you will have is that as you are supplying power into an unbalanced three phase circuit on only two phases is that the Neutral will have to carry all the return current. Also remember that the waveforms in a three phase circuit are 120 electrical degrees apart, so that throws more complexity into your unbalanced circuit.
I would think that keeping the total power to the single phase value of 12.748kw would be fine.
Of course the best way to run your system would be to get hold of a second hand three phase inverter, then you have no problems at all.
Hopefully someone with a better handle on the situation will chime in.
Pete
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 09:19am 01 Oct 2022
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I get them from Ignorance and trying to work it out best I could from the very little I could find on the matter.
That's why I wanted to ask the more knowledgeable for a confirmation or correction. I don't know beans about this but I was trying to learn what I could which was bugger all. One of those things that just does not seem to be addressed or I don't know the correct search terms.
Thanks for your input, it is very helpful and exactly the sort of info I was looking for!
I was aware of the neutral carrying the load of both the active phases which was why I thought ( incorrectly) the 120 O phase separation would give an overlap where more load could be carried.
Could you explain please, even in rough terms, why each phase would carry 12 KW? My thought was that 32A x 230V = 7360W and it was simply the current capacity of the cable that was the limit.
That is being each phase back to neutral for a 230V output as these will be run as 2 separate and independent single phase " Loads".
I thought that in single phase at least, it would be down to the carrying capacity of the 6MM cable I have. Likewise, Was my opinion that the practical current carrying capacity of 2.5 was around 20A although I do understand there are different ratings but that was the average.
The sparky eluded to the fact that there was some extra in the neutral line, also 6Mm due to the phase seperating but couldn't remember how it worked or what it worked out at.
I just need to know what the Limits are on putting these 2 single phase inverters on 2 poles with a common neutral and if I can gain some hard to find knowledge alone the way. so much better and appreciated! :0)
I would like to have a 3 phase inverter, they are bigger and cheaper than the single phases but unfortunately my metering won't allow for that.
mab1 Senior Member Joined: 10/02/2015 Location: United KingdomPosts: 209
Posted: 09:41am 01 Oct 2022
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Hi Dave 230v x 32a = 7300w max per phase 400v x 32a = 12800w max between 2 ph For resistive loads: luckily, gtis operate near unity powerfactor so should approximate a resistive load.
4kw gti at 230v = 17.4a 5kw gti at 230v = 22a
Formula (from internet) for calculating neutral current: In = sqrt ( A^2 + B^2 +C^2 - AxB - AxC - BxC)
= sqrt (302 + 484 + 0 - 383 - 0 - 0 ) = sqrt 403
= 20a
If it's just the gtis connected i don't see an issue, but bear in mind if you have loads connected as well as the gtis on the same circuit then you can draw 32a per phase from the grid plus whatever the gti is producing: up to 54A
Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9306
Posted: 12:27pm 01 Oct 2022
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Deleted duplicate posts from mab1.Smoke makes things work. When the smoke gets out, it stops!
mab1 Senior Member Joined: 10/02/2015 Location: United KingdomPosts: 209
Posted: 01:53pm 01 Oct 2022
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Thanks for that grogster :) i had an Internet glitch when i posted it and was afraid it would lose all my typing - evidently managed to hit post again twice, but didn't know how to delete the duplicates.
Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9306
Posted: 12:21am 02 Oct 2022
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It's no problem, and my comment was only for the forums information. Only admin can delete duplicate posts. You can edit or delete your most recent one, but the ones above you cannot. Smoke makes things work. When the smoke gets out, it stops!
phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2135
Posted: 12:23am 02 Oct 2022
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Is the outlet 4 pin or 5pin? If it's 4 there is no neutral.
Assuming 5 pin, the neutral current is the vector sum of the 3 actives. If they all have the same PF the currents are:-
L1 L2 L3 N 32 0 0 32 32 32 0 32 32 32 32 0
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1578
Posted: 09:43am 03 Oct 2022
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Thank you for the replies.
It seems I am good To run 2x 5 KW inverters, 20A, on 2 individual phases with both tied back to Neutral.
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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