Anyone Else Outraged About 3 Phase?

[Monkeh]

So we went down the same 110V path here in Europe but then noticed its not really that good of an idea, so we said fuck it, we are gonna do it properly and switched to 230/400V 3 phase running down whole streets. The efficiency of the new system is so much better that we don't even have polepigs. We simply plonk down one giant transformer at the beginning of the street, run the usual 20kV feed to it then run 230/400V straight down the street and connect houses directly to the pole. A single low voltage run down the street might have 30 to 100 houses connected to it. And one transformer might have 3 or 4 such runs coming off it. The wires running over the poles is not even that thick. We only have 2 kind of mains plugs, normal single phase ones for all appliances(even heavy ones) and standard 3 phase plug that is identical to ones used in industry but people have in homes.

So its not that America was first. They just never bothered to switch to the superior system and stuck to the outdated one... much like what they did with the metric system.

But as has been laid out already, we have 240V here too and have for many years. What makes single phase outdated and what true advantage does 3 phase offer for residences? Different does not mean inferior, and we've had 3 phase power in the US for a very long time, it has just never been commonly used in houses because it isn't necessary. Houses have few large induction motors, and simple, reliable 3 phase motors are the primary advantage of 3 phase. If I could upgrade my house to 3 phase service for the ridiculously low price of $100 I wouldn't bother. Why would I? What advantage would it bring over this "obsolete" system that I'm using? How do you sell it to a non-technical person who knows nothing about electricity?

With the current emerging trend of.. what's the popular term, microgeneration? Prosumering? Solar panels at scale, three-phase supplies make balancing far easier. Otherwise, it makes larger loads more practical (none of this giant aluminium trouble to run AC, no start and run caps..).

[Berni]

So we went down the same 110V path here in Europe but then noticed its not really that good of an idea, so we said fuck it, we are gonna do it properly and switched to 230/400V 3 phase running down whole streets. The efficiency of the new system is so much better that we don't even have polepigs. We simply plonk down one giant transformer at the beginning of the street, run the usual 20kV feed to it then run 230/400V straight down the street and connect houses directly to the pole. A single low voltage run down the street might have 30 to 100 houses connected to it. And one transformer might have 3 or 4 such runs coming off it. The wires running over the poles is not even that thick. We only have 2 kind of mains plugs, normal single phase ones for all appliances(even heavy ones) and standard 3 phase plug that is identical to ones used in industry but people have in homes.

So its not that America was first. They just never bothered to switch to the superior system and stuck to the outdated one... much like what they did with the metric system.

But as has been laid out already, we have 240V here too and have for many years. What makes single phase outdated and what true advantage does 3 phase offer for residences? Different does not mean inferior, and we've had 3 phase power in the US for a very long time, it has just never been commonly used in houses because it isn't necessary. Houses have few large induction motors, and simple, reliable 3 phase motors are the primary advantage of 3 phase. If I could upgrade my house to 3 phase service for the ridiculously low price of $100 I wouldn't bother. Why would I? What advantage would it bring over this "obsolete" system that I'm using? How do you sell it to a non-technical person who knows nothing about electricity?

Alright here are the benifits:
1) 3 phase needs 4 wires to transfer 3x the power of single phase that needs 2 wires. So more power per wire
2) The 3 phases cancel out reducing the current in the neutral conductor to near zero, it only carries the current imbalance, this halves the conduction losses for a cable run.
3) Interphase voltage becomes 400V and so offering 4x the power over the same thickness of copper wire versus 110V

Notice i haven't even gotten to 3 phase motors, these are all just benefits in power distribution that lets us run 100+ houses directly from a single transformer rather than having pole pigs. But 3 phase motors have been significant in the old times before VFDs. We also don't have high population density here and a lot of land are farms, to any farm you go you will see machines with 3 phase motors everywhere due to there superior power and lower weight, 3 phase outlets on every corner to power them from.

And by the way Australia has 10 times lower population density than the US, guess what they use?

[tautech]

And by the way Australia has 10 times lower population density than the US, guess what they use?

Very similar to us in NZ, 235VAC single phase and 415VAC 3 phase.

Not sure about their distribution networks but probably similar to ours:
Long range transmission backbone 400 KV DC
Medium range 220 KV AC
Some 110 KV
Regional feeders 33 KV
Terminal feeders 11 KV

[Circlotron]

This food fight about whether 120VAC either side of a centre tap is 1 or 2 phases; this is my take on it. The number of phases is equal to the number of different zero crossing points with respect to neutral. So you may have 6 different lines but only 3 different zero crossing moments so I say that's 3-phase.

With 2 sinewaves 90 deg apart you have 2 different zero crossing points so that's definitely 2-phase, but a single phase transformer with a centre tapped secondary does not produce 2-phase.

6 different lines? You'd never see such a thing. There are only two basic configurations here, and both start with a 3 phase medium voltage (usually 7200V/13500V). One of these configurations is 3 phase 120/208V using 3 transformers or a single 3 phase transformer delivering 3 live phases and neutral over 4 wires. The other is the typical residential distribution which takes one of the three 7200V (to neutral) phases and a transformer with a single center tapped 240V secondary and delivers this single phase 120V-Earth-120V to the house over 3 wires. There are never center tapped secondaries on a 3 phase system and there is still only one phase with the 120/240V arrangement. It's one or the other, 3 phase or single phase, there is no technological reason they couldn't supply 2 phase power but it isn't done.

Oh, okay. My bad. I imagined a (sort of) star secondary with 6 ends and the centre neutral point grounded.

[Circlotron]

There are never center tapped secondaries on a 3 phase system and there is still only one phase with the 120/240V arrangement. It's one or the other, 3 phase or single phase

Likely you could centre tap all three secondary windings and join them and take them down to ground. Wouldn't tolerate any unbalanced voltages though. Would make for lots of circulating currents. In that respect I suppose it would behave like a zigzag transformer. Is that topology ever used in practice?

[Nerull]

Whatever is grammatically most correct doesn't really matter, colloquially at least it is referred to as "single phase power" and technical people know that it is a single split phase.

Single phase...  Sure...  Split phase...  Sure!

It is just most certainly not TWO PHASE!   

Your ignorance is no reason for  everyone else to change their language.

https://en.wikipedia.org/wiki/Two-phase_electric_power

They're rare, but they are called "two phase". Calling it "two phase" instead of "two phases" is no different than calling three phase "three phase" instead of "three phases", and no one seems to to be getting apoplectic about that.

[Berni]

This food fight about whether 120VAC either side of a centre tap is 1 or 2 phases; this is my take on it. The number of phases is equal to the number of different zero crossing points with respect to neutral. So you may have 6 different lines but only 3 different zero crossing moments so I say that's 3-phase.

With 2 sinewaves 90 deg apart you have 2 different zero crossing points so that's definitely 2-phase, but a single phase transformer with a centre tapped secondary does not produce 2-phase.

6 different lines? You'd never see such a thing. There are only two basic configurations here, and both start with a 3 phase medium voltage (usually 7200V/13500V). One of these configurations is 3 phase 120/208V using 3 transformers or a single 3 phase transformer delivering 3 live phases and neutral over 4 wires. The other is the typical residential distribution which takes one of the three 7200V (to neutral) phases and a transformer with a single center tapped 240V secondary and delivers this single phase 120V-Earth-120V to the house over 3 wires. There are never center tapped secondaries on a 3 phase system and there is still only one phase with the 120/240V arrangement. It's one or the other, 3 phase or single phase, there is no technological reason they couldn't supply 2 phase power but it isn't done.

Oh, okay. My bad. I imagined a (sort of) star secondary with 6 ends and the centre neutral point grounded.

Actually this is one of those weird 230V delta transformers used in Norway.

Most other places will use distribution transformers that are wired for Delta on the high voltage input but wired for Y for the output so that it can have a neutral connection. But you could give it 120V center taps just the same.

[Monkeh]

Whatever is grammatically most correct doesn't really matter, colloquially at least it is referred to as "single phase power" and technical people know that it is a single split phase.

Single phase...  Sure...  Split phase...  Sure!

It is just most certainly not TWO PHASE!   

Your ignorance is no reason for  everyone else to change their language.

https://en.wikipedia.org/wiki/Two-phase_electric_power

You'll note that describes a true two-phase system with phase rotation. Split-phase, being 180 degrees out, has no rotation, which is why it is not equivalent to a two-phase system or two phases out of a three-phase system.

Actually this is one of those weird 230V delta transformers used in Norway.

Actually, it's one of those weird delta transformers used in the US to cover their mess of incompatible systems.

[Monkeh]

Likely you could centre tap all three secondary windings and join them and take them down to ground.

That would be the equivalent of taking the end of each winding down to ground. Also known as a short circuit, or at these energy levels, an explosion.

[Berni]

Actually, it's one of those weird delta transformers used in the US to cover their mess of incompatible systems.

I see... so then the 120V neutral is only a neutral for the 120V system while the 3 phase runs the Norway way of having no neutral.

Well at least this meant that the giant 3phase 5kW rack mount PSU i bought from the US on the cheap could run on our EU power by just connecting it across neutral and one phase (it didn't care about the 3rd phase missing).

[Monkeh]

Actually, it's one of those weird delta transformers used in the US to cover their mess of incompatible systems.

I see... so then the 120V neutral is only a neutral for the 120V system while the 3 phase runs the Norway way of having no neutral.

Indeed. 120V loads use the neutral, 240V loads use any phase they like (or all three), and I believe 208V single-phase loads can be put across the high leg to the neutral, but I'm not sure why you'd bother as 208V only exists as a crappy compromise for having three-phase with 120V to neutral.

And on top of all that they've got 480V three-phase which isn't compatible with any of the rest, so there's a whole other category of 277V single-phase gear for that..

So to summarize: 120V single-phase, 208V single-phase, 208V three-phase, 240V single-phase, 240V three-phase, 277V single-phase, and 480V three-phase.

ROW, mostly: 240V single-phase, 415V three-phase. Your nominals may vary.

[george.b]

Here is a fun fact, a lot of Europe used to be 110V/120V but then everyone ended up going to 220V/240V that by now got standardized to 230V

In fact a firehouse here in Slovenia (Or was it Italy, land might have changed hands in that time) has a old lightbulb that has been continuously running for a ridiculus amount of years (Much like the oldest lightbulb in new york or what was it) and is so old that it initially ran off 110V. When they switched over to 220V they wanted the old bulb to keep going so they added another 110V bulb in series.

So we went down the same 110V path here in Europe but then noticed its not really that good of an idea, so we said fuck it, we are gonna do it properly and switched to 230/400V 3 phase running down whole streets. The efficiency of the new system is so much better that we don't even have polepigs. We simply plonk down one giant transformer at the beginning of the street, run the usual 20kV feed to it then run 230/400V straight down the street and connect houses directly to the pole. A single low voltage run down the street might have 30 to 100 houses connected to it. And one transformer might have 3 or 4 such runs coming off it. The wires running over the poles is not even that thick. We only have 2 kind of mains plugs, normal single phase ones for all appliances(even heavy ones) and standard 3 phase plug that is identical to ones used in industry but people have in homes.

So its not that America was first. They just never bothered to switch to the superior system and stuck to the outdated one... much like what they did with the metric system.

Here's another fun fact, then: here in Brazil, we use both 127/220V standards (the good thing about standards is that there are so many to choose from, right? ), and we still call 127V "110" because that's what it used to be way back when. It can be 220V in one state and 127V in the next, or in some cases 220V in one city and 127V in the next... or you can get two phases from a 127/220V 3-phase system and have both in the same place. All sockets being exactly identical and it being up to you to know or indicate which one is which, of course.
My sister, who was living in a 127/220V state, blew up the power supply on her computer twice when she came over to visit (I live in a 220/380V state) because both times she forgot to flip the voltage switch. People who constantly travel between states with different voltage standards have to keep this sort of thing in mind, although it's less of a problem nowadays, with "voltage-agnostic" power supplies.

[Siwastaja]

Given two sinusoidal signals of amplitude \$V : A = V sin (\omega t + \phi_1) \text{ and } B = V sin (\omega t + \phi_2) \text { where } \phi_1 \neq \phi_2 \$ we would say that we were presented with two phases. The phase angles are different.

Why is this a special case when \$ \phi_1 \neq \phi_2  \text{ and } \phi_1 = 0, \phi_2 = \pi\$?

Vectors with exact opposite direction (180 degree phase difference), so that they are parallel to each other, cannot define a 2D space, only 1D space, and as a result, they cannot provide rotational vector, so such system cannot be used to produce a decent motor.

Or, looking it in different way, you can always create the inverted (180 deg shifted) waveform. A single-phase motor does this; some of the windings are wound in opposite direction, providing the 180 deg shifted pole of the pole pair. A full-bridge rectifier also does this.

Even a 3-phase motor does this; the minimum practical number of poles is 6 (for a 3-phase, 2 pole (= 1 pole pair) motor), and of each pole pair, one of the pairs is inverted.

So a single phase system easily allows generation of 0 deg and 180 deg vectors, wherever you need them, doing it earlier at the transformer adds no value compared to doing it at the motor. (Actual phases with phase shift not 0 or 180 deg can be generated by LC circuits, provided by run/start capacitors with single phase motors, and once the motor is running and storing momentum, a truly single-phase pulsating 1D vector can provide some torque with high ripple to keep it running.)

So a 180deg phase shifted second "phase" does not provide anything which already isn't available with a single phase wire. That's why we don't count it.

A "real" 2-phase system has the phase shift of 90 degrees; motors can then provide 0, 90, 180, 270 deg poles by choosing the winding direction per pole. This defines full 2D space and allows a true rotational torque vector. Such 2-phase systems are almost non-existing but we mentally use them to model 3-phase motors.

So yeah, we could define word "phase" in whatever way we want, for example, an imaginary 5-phase system could have the following phase shifts: 0 deg, 0 deg, 0 deg, 0 deg, 0 deg. But as a practical result, it would be identical to the single phase system.... just like systems that contain phases with +pi rad offset to already existing phases. These phases are not very useful. Hence, we talk about split-phase instead of 2-phase, and leave the term "2-phase" for the "true" 2-phase system with 90 deg phase shift.

Stepper motors are the most widely used case of 2-phase power system, although that may not be obvious to anyone looking at them first. When you microstep a "bipolar" stepper and look at the waveforms, you start to understand what's happening.

[mzzj]

In my parents home even my bedroom had 3x16A 3-phase outlet 

Cool!  Could someone post a pic of that? I'm familiar with industrial strength 3-phase outlets but never seen a domestic one here in Australia. I have 3-phase at home. Cost me an extra AUD$200 when the house got built in 1994. Instead of 1x100A I got 3x60A. That's what would fit in the underground conduit from the street to the house. Would have much rather had 3x100A of course. I was involved with 3-phase induction motor SCR soft starters / power savers at the time. Never actually got around to using it at home. Nowadays general power is on one phase, aircon and solar is on second and lighting on third. 240/415 here.

It wasn't really any living room decoration, just normal 3x16A "industrial" outlet like this
https://www.ikh.fi/images/wwwkuvat/Tuotekuvat/CRX4021_S_1_web.jpg

we have also this sort of 3-phase outlets if you want bit more refined looks:

[Circlotron]

Likely you could centre tap all three secondary windings and join them and take them down to ground.

That would be the equivalent of taking the end of each winding down to ground. Also known as a short circuit, or at these energy levels, an explosion.

Thinking about it further, yes, you are right. If A phase it at it's positive peak then B and C are equal and somewhat negative. Therefore the centre tap between B and C would be the same potential as B and C but the other two centre taps would be halfway between A and B or A and C. dzzzt!

[Berni]

Yep we use those IEC standard 3 phase outlets in pretty much all of EU

Tho houses older than about 30 years over here still use the Yugoslavian 3 phase outlet. Its a pretty unique looking one compared to other sockets around the world.

Its just simply the classical german Schuko socket that was already used for single phase being stretched out to give it room for the extra prongs. Most houses had at least one of these somewhere for cases when you needed to plug in something big like a big ass welder or saw.

This socket has one design flaw however. The spacing between the 3 phase prongs is the same as a normal single phase Schuko, but the body of those is too thick to fit in so you can't actually plug it in, but the compact thin itallian style EU plugs with no earth are compact enough to fit inside. When you do this you connect 400V into it and that means kaboom.

[Kleinstein]

How much it costs to get 3 phases service depends on the local installation. If they use the 3 phase system it can be cheap, if not it can be expensive because they need to run new wires and maybe transformers. So you have to live with the local system.

With underground cables the 3 phase system has some advantages (effectively higher voltage and less copper). With more pole mounted air isolated lines also for low power the split phase or 1 phase system has some advantage. In the US pole mounted wiring is a lot more common than in Europe. In Germany they are bringing also the 20 kV lines and now even new 380/400 kV underground.
3 Phase motors were also a big plus.

Old apartments can still have only 1 phase power, but this is rare and inconvenient for something like electric cooking. Usually it's still 3 phase for the house, but 1 phase per house. It makes the meters a little cheaper - though not much as 3 phase is the normal case.

For the 3 phase system there are also special 3 phase transformers, that combine all 3 phases with a 3 legged core. Using 3 separate transformers works, but uses slightly more material. It may be still an option for logistic reasons.

[madires]

A "real" 2-phase system has the phase shift of 90 degrees; motors can then provide 0, 90, 180, 270 deg poles by choosing the winding direction per pole. This defines full 2D space and allows a true rotational torque vector. Such 2-phase systems are almost non-existing but we mentally use them to model 3-phase motors.

I just checked what local universities teach EE students about multi-phase systems and found https://www.thm.de/iem/images/user/novender-978/gwds-19109.pdf. It's German - however, the diagram in section 3.19 shows a 2-phase system with the phases 180° apart.

[Siwastaja]

A "real" 2-phase system has the phase shift of 90 degrees; motors can then provide 0, 90, 180, 270 deg poles by choosing the winding direction per pole. This defines full 2D space and allows a true rotational torque vector. Such 2-phase systems are almost non-existing but we mentally use them to model 3-phase motors.

I just checked what local universities teach EE students about multi-phase systems and found https://www.thm.de/iem/images/user/novender-978/gwds-19109.pdf. It's German - however, the diagram in section 3.19 shows a 2-phase system with the phases 180° apart.

Nomenclature is arbitrary; understanding is more important. I think there is no law describing sanctions on calling split-phase system "2-phase". I recommend against doing that because it is highly confusing, while "split phase" instantly distincts the system from anything else and is easily googlable with good results. OTOH, I also recommend against assuming that someone talking about "2-phase" doesn't mean split-phase. True 2-phase (one which provides rotating 2D voltage or current vector which 1-phase or split-phase doesn't do) is such rarity, so better communicate explicitly and ask for clarification whenever someone talks about a 2-phase system.

I am also sure you'll be able to find many more errors, some much more problematic, in any number of university course materials; they are done by humans after all. I was originally hired at an Uni literally just to fix them.

[Cerebus]

Given two sinusoidal signals of amplitude \$V : A = V sin (\omega t + \phi_1) \text{ and } B = V sin (\omega t + \phi_2) \text { where } \phi_1 \neq \phi_2 \$ we would say that we were presented with two phases. The phase angles are different.

Why is this a special case when \$ \phi_1 \neq \phi_2  \text{ and } \phi_1 = 0, \phi_2 = \pi\$?

Vectors with exact opposite direction (180 degree phase difference), so that they are parallel to each other, cannot define a 2D space, only 1D space, and as a result, they cannot provide rotational vector, so such system cannot be used to produce a decent motor.

Or, looking it in different way, you can always create the inverted (180 deg shifted) waveform. A single-phase motor does this; some of the windings are wound in opposite direction, providing the 180 deg shifted pole of the pole pair. A full-bridge rectifier also does this.

Even a 3-phase motor does this; the minimum practical number of poles is 6 (for a 3-phase, 2 pole (= 1 pole pair) motor), and of each pole pair, one of the pairs is inverted.

So a single phase system easily allows generation of 0 deg and 180 deg vectors, wherever you need them, doing it earlier at the transformer adds no value compared to doing it at the motor. (Actual phases with phase shift not 0 or 180 deg can be generated by LC circuits, provided by run/start capacitors with single phase motors, and once the motor is running and storing momentum, a truly single-phase pulsating 1D vector can provide some torque with high ripple to keep it running.)

So a 180deg phase shifted second "phase" does not provide anything which already isn't available with a single phase wire. That's why we don't count it.

A "real" 2-phase system has the phase shift of 90 degrees; motors can then provide 0, 90, 180, 270 deg poles by choosing the winding direction per pole. This defines full 2D space and allows a true rotational torque vector. Such 2-phase systems are almost non-existing but we mentally use them to model 3-phase motors.

So yeah, we could define word "phase" in whatever way we want, for example, an imaginary 5-phase system could have the following phase shifts: 0 deg, 0 deg, 0 deg, 0 deg, 0 deg. But as a practical result, it would be identical to the single phase system.... just like systems that contain phases with +pi rad offset to already existing phases. These phases are not very useful. Hence, we talk about split-phase instead of 2-phase, and leave the term "2-phase" for the "true" 2-phase system with 90 deg phase shift.

Stepper motors are the most widely used case of 2-phase power system, although that may not be obvious to anyone looking at them first. When you microstep a "bipolar" stepper and look at the waveforms, you start to understand what's happening.

Ah, someone who missed the  . I was just having a poke at the prescriptivists who were bring a little bit silly about arguing over saying two phases or split phases. Looks like someone took the bait. I was impressed by the number of people who were smart enough not to fall for it.

[Siwastaja]

Ah, someone who missed the  .

Actually I didn't miss it! I just wanted to provide the explanation nevertheless, if not for you, for the others looking at this thread, because this is something worth giving a thought about; your question why 180 deg shift is different, is a really good one. Good to hear confirmation that we don't have to run in circles with this, not that I would have participated in 2nd round of trolling, anyway.

[Zucca]

20 years ago I used to wish I had 3 phase, but now I don't care. When I want to run a 3 phase motor I run it on a VFD, and I'd do the same even if I had 3 phase into the house just due to all the other features it gives you. I have no other use for 3 phase power.

1) Let's say you have 220V/240VAC 60 Hz from the grid, can your VFD get a 220V/240VAC 50Hzon the output?
I think, the answer is yes
2) Let's say you have 220V/240VAC 60 Hz from the grid, can your VFD get a 380VAC (1 or 2 or 3 phases) on  the output?
I think, the answer is no

So if I have a 220VAC 50 HZ motor from EU I can run it in US, but if I have a 380VAC equipment it will be a circus acrobatic jazz to get it working in the US.

right?

[Cerebus]

20 years ago I used to wish I had 3 phase, but now I don't care. When I want to run a 3 phase motor I run it on a VFD, and I'd do the same even if I had 3 phase into the house just due to all the other features it gives you. I have no other use for 3 phase power.

1) Let's say you have 220V/240VAC 60 Hz from the grid, can your VFD get a 220V/240VAC 50Hzon the output?
I think, the answer is yes
2) Let's say you have 220V/240VAC 60 Hz from the grid, can your VFD get a 380VAC (1 or 2 or 3 phases) on  the output?
I think, the answer is no

So if I have a 220VAC 50 HZ motor from EU I can run it in US, but if I have a 380VAC equipment it will be a circus acrobatic jazz to get it working in the US.

right?

A VFD just takes whatever supply it has and rectifies it to DC. Then it typically uses MOSFET half-bridges to PWM that DC into whatever AC waveforms you want/need.

If the required peak voltage of your output waveform is higher than the peak voltage of the input AC supply then instead of a simple rectifier bridge to get your intermediate DC bus you have to use a boost convertor to get there. Of course it is possible to combine active input rectification and a boost convertor as a single stage, and VFDs that also do power factor correction do this anyway.

So a VFD using simple rectification can produce any arbitrary frequency output, with a peak voltage up to the peak voltage of the incoming mains. Only VFDs that include a boost stage can produce a higher output voltage than input voltage.

Needless to say that in any case voltage-wise, you can have as many output phases as you like, you just need an output half-bridge for each phase.

[Zucca]

Oh I did not know about the VFD with boost.. interesting piece of kit.

What are good brand VFD? I need maybe need a VFD from 240VAC 60HZ to 240 50HZ, 3KW.
BTW, do I really need the 50Hz or VFD? I mean a 50Hz motor will get in trouble if I feed it with 60Hz?

[drussell]

I shot some video yesterday, will try to edit up a couple things to post. 

I'm headed back over to the car wash now to change out that broken pilot assembly on the west 1,200,000 BTU wash-water boiler and hopefully shoot a bit more stuff I should have thought to mention about the 3-phase electrical and where I want to upgrade to VFDs, so I can try to edit it in...

I suppose you won't know what I'm talking about on that until you see some of the video...