Is the power delivered by 1 no. of 3 phase system the same as 3 no. of 1-phase system?

[Jasper12]

is the power delivered by 1 no. of 3 phase system equal to the power delivered by 3 nos. of 1 phase system? Assuming same voltages and amps ratings

 

[russ_watters]

Welcome to PF. This looks like homework but either way should be pretty easy for you to answer. Just look up and compare the equations for power for each case. Let us know what you find.

 

[berkeman]

Welcome to PF.

is the power delivered by 1 no. of 3 phase system equal to the power delivered by 3 nos. of 1 phase system? Assuming same voltages and amps ratings

Sorry, what does the abbreviation "no." stand for in your post? Thanks.

 

[Averagesupernova]

Welcome to PF.


Sorry, what does the abbreviation "no." stand for in your post? Thanks.

I'm assuming if you replace the word "no" with "set(s)", the question will make sense.

 

[Jasper12]

no. = number , thks

 

[russ_watters]

Ok, so 20 hours later you haven't been able to google and figure this out? FYI, Physics Forums is not google and is not a chat-bot. We're a forum for learning physics/science from subject matter experts. So you need to put some effort into learning in order to take advantage of what we can offer. At this point you're 21 hours into a problem that should have taken you 30 seconds to solve based on the approach I gave you in my first reply. Our goal here is to help you fix that deficiency. Please make an effort to do so.

 

[DaveE]

is the power delivered by 1 no. of 3 phase system equal to the power delivered by 3 nos. of 1 phase system? Assuming same voltages and amps ratings

That all depends on how they are connected, and to what. It's not just "volts" and "amps", there are network and phase considerations. Please provide a more detailed description of the circuits, bonus points for a schematic!

 

[Guineafowl]

The internet can be a confusing place. In this Fluke article, they assert that 3ph can transmit 3x the power of 1ph, implying the answer to the OP is ‘yes’:

https://www.fluke.com/en-gb/learn/blog/power-quality/single-phase-vs-three-phase-power#:~:text=three-phase power, three-,three wires instead of two).

However, $3(VI)\neq \sqrt{3} VI$ (for resistive loads), so I do get the premise of the question.

Certainly a schematic would be helpful.

 

[Dullard]

"Same Voltages" is the tricky part of this question. If your single-phase supply is 120 VAC (L-N) and your 3-Phase supply is 120 VAC (L-N) [A.K.A. '208'], then the answer is 'yes.' 120*I : 3*120*I = 208*sqrt(3)*I.

 

[Gavran]

A three-phase system can serve as three single-phase systems and it can be said a three-phase system can deliver three times as much power as a single-phase system.

For high-leg delta three-phase systems this can not be said.

 

[Averagesupernova]

A three-phase system can serve as three single-phase systems and it can be said a three-phase system can deliver three times as much power as a single-phase system.

For high-leg delta three-phase systems this can not be said.

Care to expand on any of that?

 

[Gavran]

In Europe when delivering 3 phase power to the panelboard there is the same line-to-neutral voltage on all three phases and that means all three phases together can deliver three times as much power as one of them. In North America when delivering 3 phase power using a high-leg delta there is not the same line-to-neutral voltage on all three phases and that means the power delivered by a single-phase can not be the same for all three phases and all three phases together can not deliver three times as much power as any of them.

 

[onatirec]

In a single-phase machine with sinusoidal EMF instantaneous power is

e*i = EI[cosγ - cos (2ωt + γ)]

The first term represents constant power, the second term is a 2ω oscillatory torque/power superimposed on the average.

When increasing to two- or three-phase balanced machines, this secondary oscillatory term is cancelled out and the power becomes

N_phEIcosγ = (1/ω)[Σ(e_ai_a)] for a =1 -> N_ph

I'll leave it up to you to find limits on e & i in different phases to determine actual power differences within a similar sized machine.

 

[Averagesupernova]

In North America when delivering 3 phase power using a high-leg delta there is not the same line-to-neutral voltage on all three phases and that means the power delivered by a single-phase can not be the same for all three phases and all three phases together can not deliver three times as much power as any of them.

There is nothing that says a single phase load has to be from hot to neutral. There are times when a single phase load is placed between the 'wild' leg (referred to as the B leg) and one of the others (A or C). It's not prohibited by code.
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Also, there are lighting circuits that run at 277 volts in the USA. I don't get into 480 volt systems but I believe that voltage comes from the wild leg on high leg delta on 480 systems. It can also come from 480 Y leg to neutral. I was told 277 circuits exist to utilize an otherwise lightly load B leg.
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Edit. I thought about this for a bit, the math doesn't work out to have 277 on 480 delta. It must be line to neutral on 480 wye.

 

[Gavran]

There is an article (https://en.wikipedia.org/wiki/Polyphase_system) and there is an introduction in the article and there is a sentence in the introduction which claims that compared to a single-phase, two-wire system, a three-phase three-wire system transmits three times as much power for the same conductor size and voltage.

 

[DaveE]

the same conductor size

Yes, but you have more of them, so it's not the same amount of copper.

 

[Averagesupernova]

Any time conductors can be shared and opposing currents are involved we can reduce the size of the wire and save copper. Edison's original DC system did the same thing.