3 phase and Grid tie... what will happend?

[Sunking]

Kengine7 my reference is to purely resistive power to keep it simple where PT = P1 + P2 + P3.

If you want to take power factor into th equation the math is a little more complicated and I do not think many here would understand: P = √3(V * I * cos(f)) or P = 3(Vp * Ip * cos(f))

[Kengine7]

Russ I am going to give you the simple answer. It means you will have neutral current flowing of about 1.5 amps. If all three phases are perfectly balanced, you will not have any neutral current flowing in a 4 wire wye system.

Think of it like this: We have three horses bridled together to a common point pulling in 3 different directions. They are pulling 120 degrees adjacent to each other. Think a pie cut in thirds. If they apply the same force, they go no where. If one or two are pulling harder than one, the center of the circle travels at x degrees at Y speed. The math is very complicated and beyond the scope of this discussion.

But to get to what you want to know the Power adds to PT = P1 +P2 +P3 assuming there is no power factor involved with pure resistive load. Again the math is very complicated if we factor in Power factor which means angles again.

So in your questions lets assume the power factor = 1, or a purely resistive load like a resistor and then we can use Ohm's Law. The voltage is assumed to be 208 volts for a 208 delta system. So you have 1 amp in phase A and the power in Phase A = 208 volts x 1 amp = 208 watts. Phase B power = 208 volts x 2 amps = 416 watts. Phase C power = 208 volts x 3 amps = 624 watts Total power consumed = PA + PB + PC = 208 + 416 + 624 = 1248 watts.

So in a 3-phase 208/120 circuit to deliver 1248 watts the maximum current is 3 amps at this degree of unbalance. If balance so all 3 phase current are equal the current in each phase would be 2 amps in each phase. To do the same with a single phase circuit at 240 volts would require 5.2 amps, or 10.4 amps @ 120 volts.

Hopefully now you see why 3-phase and higher voltages are the way to go for higher power demand.

Here is an example: I supply a single phase 240/120 service rated at 200 amps at your house, and next door I deliver the same 200 amp service at the equivalent voltage 0f 208/120. How much power can each service deliver at a given moment in time.

Single phase can deliver 240 volts x 200 amps = 48,000 watts or 48 Kw
3-phase can deliver 208 volts x 200 amps x 3 phases = 124,800 watts or 124.8 Kw

Understand?

Check your math below.

[Kengine7]

How about 200 x 120 x 3 or 208 x 200 x 1.73?

[Kengine7]

Europe, huh?

If you have three phase and the line to line voltage is within the inverter specs I would think that the inverter would present as a source parallelled with those two lines. I have parallelled single phase generators to individual legs of a 120/208 wye genset. The application was a 3 phase motor and a 15 amp single phase load. To offset the imbalance and reduce heat from a single phase I paralled a 1500 watt 120-vac generator to the loaded leg. Before you say anything, the small generator could not handle 15 amps continuous and the 3 phase was too expensive to risk the heat.
Based on experimentation consider the inverter on the highest loaded lines.

[Sunking]

can you tell me what happens if the load is not balanced between the three phases say 1 amp on one leg, 2 amps on the second and 3 amps on the third?

Russ I am going to give you the simple answer. It means you will have neutral current flowing of about 1.5 amps. If all three phases are perfectly balanced, you will not have any neutral current flowing in a 4 wire wye system.

Think of it like this: We have three horses bridled together to a common point pulling in 3 different directions. They are pulling 120 degrees adjacent to each other. Think a pie cut in thirds. If they apply the same force, they go no where. If one or two are pulling harder than one, the center of the circle travels at x degrees at Y speed. The math is very complicated and beyond the scope of this discussion.

But to get to what you want to know the Power adds to PT = P1 +P2 +P3 assuming there is no power factor involved with pure resistive load. Again the math is very complicated if we factor in Power factor which means angles again.

So in your questions lets assume the power factor = 1, or a purely resistive load like a resistor and then we can use Ohm's Law. The voltage is assumed to be 208 volts for a 208 delta system. So you have 1 amp in phase A and the power in Phase A = 208 volts x 1 amp = 208 watts. Phase B power = 208 volts x 2 amps = 416 watts. Phase C power = 208 volts x 3 amps = 624 watts Total power consumed = PA + PB + PC = 208 + 416 + 624 = 1248 watts.

So in a 3-phase 208/120 circuit to deliver 1248 watts the maximum current is 3 amps at this degree of unbalance. If balance so all 3 phase current are equal the current in each phase would be 2 amps in each phase. To do the same with a single phase circuit at 240 volts would require 5.2 amps, or 10.4 amps @ 120 volts.

Hopefully now you see why 3-phase and higher voltages are the way to go for higher power demand.

Here is an example: I supply a single phase 240/120 service rated at 200 amps at your house, and next door I deliver the same 200 amp service at the equivalent voltage 0f 208/120. How much power can each service deliver at a given moment in time.

Single phase can deliver 240 volts x 200 amps = 48,000 watts or 48 Kw
3-phase can deliver 208 volts x 200 amps x 3 phases = 124,800 watts or 124.8 Kw

Understand?

[russ]

Hi Sunking, Nothing to do with solar but can you tell me what happens if the load is not balanced between the three phases say 1 amp on one leg, 2 amps on the second and 3 amps on the third?

Would you be drawing more through the meter than with a balanced load?

Thanks
Russ

[Sunking]

While you guys was flaming me here on forum

I do not think anyone was flaming you, I certainly was not trying too. My comment about a mansion and servants was just humor. The reason I said that I have already explained, 3-phase service is for very large load demand are rarely used for a residence unless it is a very large home the size of a mansion, so large it would require a staff of servants to maintain and operate with separate living quarters.

[Mike90250]

You can feed 1 phase GT inverter into 1 leg of a 3 phase circuit, but I don't knwo how the meter will interpret that, and at some point, the service transformer will become un-balanced. I'd think 10-20% of service capacity would be OK. (if you have 100A service, you an backfeed 20A on 1 leg before something complains)

[nordashi]

[QUOTE=MarineLiner;10201]

[MarineLiner]

Please do not underestimate my knowledge. It's a 3 phase.
It's not allowed, but that is not the point. Reread my post.

[Sunking]

What are you talking about?

I think the question is what are you talking about?

I live in Europe, and our electrical system is different.

I am very familiar with European electrical architecturre as I have designed many systems for clients there. Eurpoean electrical systems are no different than what we use in the USA other than the standard residential service is 220-240 single phase service operating at 50 Hz, compared to the USA 240/120 volt single phase service.

There are huge transformation stations (in my small town there are 4 of them) which feed 3 phase.
One house is connected to 1st phase, 2nd is to the 2nd, ...
and that how balancing is made.

That is how every electrical distribution service in the world is constructed. However what you just described for residential service IS NOT 3-PHASE, It is Single Phase just like it is done on every where in the world. The distribution is 3 phase, but for your residential electrical service you are only connected to 1 of the 3 phases via a transformer to step the voltage down from say 13.2 Kv to 220 volts.

So go ahead and take that picture and I will show you what is really happening.

[nordashi]

Are you sure it's 3 phase?
Is not it a 3 circuit breaker (fuse) box?
Anyway, please be carefull and check: do you allowed to connect by yourself?

Please do not underestimate my knowledge. It's a 3 phase.
It's not allowed, but that is not the point. Reread my post.

3 phase for a house? What size of a mansion do you live in and how many servants work for you? The answer to your question is you buy a 3-phase inverter, but I have no idea how you will balance 3 phase with a bunch of mixed single phase loads. Well actually I do but it requires some expensive transformers.

Mansion? 3 phase? What are you talking about?
I live in Europe, and our electrical system is different.
There are huge transformation stations (in my small town there are 4 of them) which feed 3 phase.
One house is connected to 1st phase, 2nd is to the 2nd, ...
and that how balancing is made.

All cables for 3 phase are passing every house so it's cheap to connect onto 3 phase. You can have 3phase even if you had a 1 room house.
My 3 phase is used for mill, Hydrofor (erm water pump), metal welder, circular saw, ...


If you don't believe I'll make a video.
Lets get back to my question?

[Sunking]

Well Poly or 3 phase circuits are probable outside the scope on this forum as most are DIY types and do not have much understanding of electrical circuits.

3 phase power is used a few different ways. Most prominently used by all commercial power generation and distribution. It allows electric companies to distribute large amounts of power on small and few conductors as possible. Enough about that as you do not need to know anymore about it with respect to generation and transmission.

On the user side 3-phase power is the standard for large commercial and industrial users where large electric motor loads are used. 3 phase motors are far more efficient and simple than their Single phase cousins.

In North America generally 3 phase does not enter in residential homes unless the home is really large, or a multi-residential complex like apartment or high rises. Even where it does, it is usually split out at the main distribution board and the individual loads are fed from a single phase. However where it is used the voltage is not 240/120 like single phase, it is 208/120. If your large appliances like hot water heaters, air conditioners, stoves, and ovens will have to be able to use the lower 208 voltage usually by a tap inside the unit. Not all appliances have this feature. To have true 3-phase appliances like air conditioning, hot water, etc can be had at a premium price, and if your home is large enough to justify 3-phase, you can afford the premium price IMHO. The plus is your heating and cooling bills will be lower.

[russ]

No - think you might not understand 3 phase - all three phases are fed to the motor of whatever you are operating.

More efficient than single phase - similar as using HT power for larger motors. I suppose you could operate a large motor on household 120 volt power but it would be one very expensive motor and the power costs would be frightening.

[MarineLiner]

Depends on where you are located.
I have 3 phase power - used for the water pumps and heat pump.

also something like:
P1 for water pumps,
P2 for heat pump,
P3 for other uses ?

I had replaced an engine with a 1HP electro motor, to rotate an air compressor for underwater ballerina,
wich use 3phase power, but my electrician friend do the connections.
I did the easiest part, adjusting the air pressure switch. Ha ha ...