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Inverter 3 Phase Questions


Jack007

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Good day, i realise that this is probably more a electrical question, but i would like to ask it here due to inverters being part of the equation.

i would like to have the ability to power 3 Phase equipment. Up to now ive only had experience with 230V.

Q1: If one has a sentral system feeding 3 seperate buildings, can building 1 be fed single phase; building 2 be fed single and 3 phase; and building 3 be fed single and 3 phase as well?

Q2: How would this be done on a wire level? Q2.2 Would the buildings being fed single as well as 3 phase need sperate wires for both 3phase and single phase or could one simply "tap" single phase from the 3 phase wires at the destination?

Q3: I understand that the phases should be balanced, would this setup cause issues in this regard?

Q4: Would i need a 4th inverter to only feed the single phase usages separately?

Q5: Could additional inverters be added to a phase to increase its kw capacity? Q5.2 What would this mean in terms of the total 3phase capacity and phase balance then?

Q6: If 3x 8kw inverters are used to generate 3phase, what would the total 3phase capacity be? Would it be able to power a 8kw or 24kw 3phase motor? Q6.2 How would single phase fit into this equation in terms of capacity available?

Thank you so much for your explanation.

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3 hours ago, Jack007 said:

Q1: If one has a central system feeding 3 separate buildings, can building 1 be fed single phase; building 2 be fed single and 3 phase; and building 3 be fed single and 3 phase as well?

Yes.

3 hours ago, Jack007 said:

Q2: How would this be done on a wire level?

Single phase is just one phase (any will do) and neutral.

3 hours ago, Jack007 said:

Q2.2 Would the buildings being fed single as well as 3 phase need sperate wires for both 3phase and single phase or could one simply "tap" single phase from the 3 phase wires at the destination?

No need for extra wires for single phase.

3 hours ago, Jack007 said:

Q3: I understand that the phases should be balanced, would this setup cause issues in this regard?

Different utilities have different requirements in this regard. But in general, it doesn't matter all that much. Loads tend to average out across the phases, and if they don't, the utility can change one or more customers from one phase to another.

3 hours ago, Jack007 said:

Q4: Would i need a 4th inverter to only feed the single phase usages separately?

No. A three phase inverter is like three single phase inverters in one box. It can get a little tricky sorting out the currents that will flow when you have genuine 3-phase loads and single phase loads.

3 hours ago, Jack007 said:

Q5: Could additional inverters be added to a phase to increase its kw capacity?

Usually, yes. Though if you have a 3-phase inverter, usually these will not want to talk to a single phase inverter. With Axperts for example, you usually install three identical inverters for 3-phase, but you can add a fourth, fifth or more identical inverter to the setup to beef up one or more phases. These inverters have to be physically close to each other to be paralleled; you can't have inverters in separate buildings in parallel.

3 hours ago, Jack007 said:

Q6: If 3x 8kw inverters are used to generate 3phase, what would the total 3phase capacity be?

24 kW.

3 hours ago, Jack007 said:

Would it be able to power a 8kw or 24kw 3phase motor?

Ignoring start-up currents for now (and these are very significant, often 5x - 7x the full load current), you could run a 24 kW load such as a 24 kW motor.

3 hours ago, Jack007 said:

Q6.2 How would single phase fit into this equation in terms of capacity available?

Let's say you have a 9 kW three-phase load. It could be connected star (phase to neutral) or delta (phase to phase); it doesn't matter, each inverter will be providing 3 kW either way. So those inverters would each have 5 kW capacity left over for single phase loads. If you had say a 6 kW single phase load, you could not run it, even though you have 15 kW capacity spare (24 - 9 = 15), since each inverter only has 5 kW capacity left over.

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16 minutes ago, Coulomb said:

Yes.

Single phase is just one phase (any will do) and neutral.

No need for extra wires for single phase.

Different utilities have different requirements in this regard. But in general, it doesn't matter all that much. Loads tend to average out across the phases, and if they don't, the utility can change one or more customers from one phase to another.

No. A three phase inverter is like three single phase inverters in one box. It can get a little tricky sorting out the currents that will flow when you have genuine 3-phase loads and single phase loads.

Usually, yes. Though if you have a 3-phase inverter, usually these will not want to talk to a single phase inverter. With Axperts for example, you usually install three identical inverters for 3-phase, but you can add a fourth, fifth or more identical inverter to the setup to beef up one or more phases. These inverters have to be physically close to each other to be paralleled; you can't have inverters in separate buildings in parallel.

24 kW.

Ignoring start-up currents for now (and these are very significant, often 5x - 7x the full load current), you could run a 24 kW load such as a 24 kW motor.

Let's say you have a 9 kW three-phase load. It could be connected star (phase to neutral) or delta (phase to phase); it doesn't matter, each inverter will be providing 3 kW either way. So those inverters would each have 5 kW capacity left over for single phase loads. If you had say a 6 kW single phase load, you could not run it, even though you have 15 kW capacity spare (24 - 9 = 15), since each inverter only has 5 kW capacity left over.

Thank you so so much @Coulomb for taking the time to answer my questions. I really do appreciate it tremendously.

Quote

Let's say you have a 9 kW three-phase load. It could be connected star (phase to neutral) or delta (phase to phase); it doesn't matter, each inverter will be providing 3 kW either way. So those inverters would each have 5 kW capacity left over for single phase loads. If you had say a 6 kW single phase load, you could not run it, even though you have 15 kW capacity spare (24 - 9 = 15), since each inverter only has 5 kW capacity left over.

What if that 6kw single phase load was allowed to draw power from 2 or 3 of the phases in a parallel type fasion in order to keep the voltage the same but to allow for higher current? Is this possible - as i understand the phases are displaced by 120deg

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10 hours ago, Jack007 said:

What if that 6kw single phase load was allowed to draw power from 2 or 3 of the phases in a parallel type fashion in order to keep the voltage the same but to allow for higher current? Is this possible - as i understand the phases are displaced by 120deg

Because they are 120° apart, there is 400 V between them. So you can't parallel them; this would effectively be short circuiting a stout 400 V supply.

This is the frustration of separated loads or a even 3-phase setup. There can be situations where you have plenty of capacity, but because of the configuration, you can't use it all. If you parallel all on one phase, that never happens, because all the paralleled inverters share the load about equally.

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11 hours ago, Jack007 said:

Which inverters are known to parallel/do well in 3phase setups?

I only know the Voltronic Axperts (with various brand names); I believe that most inverters from manufacturers have similar arrangements, but I have no idea of the details for them.

With Axperts, you can't parallel the very small model, usually you need at least 4 kVA before they have the paralleling ability. But above this power level, pretty much all models can be paralleled, EXCEPT the VM models (e.g. Kodak OG with no further letters or characters like +). These VM models are the "value" models, that have a smaller processor that doesn't have room for all the paralleling firmware support.

You usually need one paralleling kit for each inverter to be paralleled or 3-phased. With 3 phase, you need at least  3 inverters, you can't do 2 (and there would be no point). A few models come with a paralleling board already installed, and presumably one set of paralleling cables comes with.

As for do well, the Axperts (which I regard as just barely good enough) seem to do OK most of the time with paralleling; I have a pair of paralleled Axperts myself (PIP-4048MS). Once set up properly, they seem to do fine, except for the occasional report of fault code 60 (power feedback protection). Even that seems to be an installation problem. I had a problem with one of my paralleling boards that was affected by nearby lightning, and was able to repair it myself.

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