WBahn, firstly there is only one STATOR in a power generator. In Xanadu, I'm sure they can have whatever they wish as far as windings on their STATORS go but they would find it to be very impractical to have a winding or even a single coil per degree of STATOR circumference as I'm sure the output would not be too useful for large scale power generation. May be fun as a novelty to try this.
I am not aware of any 6-phase machines but I guess this would be possible but I don't know of any such system used for large scale power.
Yes, if N=3 as per your post then this would be a 3 phase machine as is used in most power stations and distributed as such.

 

OK I believe we all can agree "American 120/240 Vac power is derived from a center tapped utility transformer". This is a given and covered in this AAC article. That utility transformer is fed by a single phase. So the question becomes can I start with a single phase, one of three high voltage lines on the utility line and have a transformer convert a single phase into poly phase? I believe thus the term "split phase". I don't know of any transformer that creates poly phase from single phase. This is how I have always viewed it anyway.

Ron

 

Our utility references the 120v/240v service coming to the residence as a single phase service.
It is one phase that comes down to the transformer that will serve approximately 6 homes maximum with the two 120v lines so that you can supply 120v to your 120v appliances from each side of a breaker box. When properly balanced, you are using both sides to service the home.
The reason for 2 x 120v lines is so that your residence can also be supplied with 240v power for your 240v appliances such as the air conditioner unit on your home.
This is all still considered a single phase. The same phase is separated by 180' at the transformer so that you can connect them together at a double breaker in the box to get 240v without that single phase bucking into itself.
A 2 phase system is what the utility company calls a network system. These are two separate phases pulled off of a three phase system. The three phase system is 120' apart, thus 360' with all three phases considered. The two phases used for networking are 120' apart. Thus the voltage for this service is 120v/208v. This is typically found at apartment complexes here in the U.S.
Electric heaters in the apartments will use the 208v. This is how the utility company balances big loads, by using more than one phase at a heavier loaded site(due to the amp draw from electric heaters/multiple dwellings).

 

OK I believe we all can agree "American 120/240 Vac power is derived from a center tapped utility transformer". This is a given and covered in this AAC article. That utility transformer is fed by a single phase. So the question becomes can I start with a single phase, one of three high voltage lines on the utility line and have a transformer convert a single phase into poly phase? I believe thus the term "split phase". I don't know of any transformer that creates poly phase from single phase. This is how I have always viewed it anyway.

Ron

You can mimic 3 phase with a single phase locally, such as for a personal hobby project. Were you intending on asking the utility company to try and provide this service for you? Do you need three phase power and don't have a 3-phase service near you; like at a business next door? I don't believe the utility company will provide such a means to do as you ask. They will likely ask you to have the 3-phase service installed. If you are trying to figure out how to run 3-phase motors from your home, you will have issues with loading up on that single phase service.

 

There are ways to run a 3-phase motor using phase-shift capacitors from a single phase but the motor efficiency suffers and its maximum power is lower.

 

Isn't it just the transformers config? Delta vs. Wye.

In this article I thought it was and is an explanation of the phase relationships. http://phasetechnologies.com/phaseconverterinfo/phaseconverter_deltawye.htm

 

You can mimic 3 phase with a single phase locally, such as for a personal hobby project. Were you intending on asking the utility company to try and provide this service for you? Do you need three phase power and don't have a 3-phase service near you; like at a business next door? I don't believe the utility company will provide such a means to do as you ask. They will likely ask you to have the 3-phase service installed. If you are trying to figure out how to run 3-phase motors from your home, you will have issues with loading up on that single phase service.

No, I have no need for three phase service? Actually we have two three phase lines running down my street. We have 13.3 KV and also 25 KV. Now as a side note I know a guy who was out towards the country. His machine shop began small so three phase machines were run off motor/generators (Inverters weren't popular yet). In his case twenty five years ago, as he grew he talked to First Energy about three phase service. To get the nearest 3 phase service and run him 480 Volt 3 Phase his cost would have been around $50,000. The only high voltage line in the area was single phase. As the area grew and three phase got closer the price dropped. Several years ago he finally got the service for about $25,000. Anyway, personally I have no need for it. Had a heck of a pile of 220 Volt single phase motor generators to sell.

Ron

 

Looking at it another way,

Each phase supply 1, 2, 3, or 100 is supplied and measured between the phase line and the return line.

If the return line is common to all phases, then consider the effect of connecting a split phase supply to two terminals of a device.
The split phases will always be opposite, resulting in a constant zero output.

A pair of genuine two phase supplies will both drive the device at their appropriate times.

So in this instance I agree with crutschow.

 

On a side note and off topic thought I would share a story of several months ago. This is about 3 phase power and a few metallic mylar balloons. We have all seen those shinny foil looking balloons. Yes, they really are conductive. Several months ago, when the trees actually had leaves our neighbor's granddaughter managed to let go of a few such balloons. Beyond the usual 220 VAC service above that we have 13.3 KV service and above that 25 KV service, all 3 phase service. When the kid lost her balloons grandma took a picture.



Those balloons are caught on a 13.3 KV line. The following day around midday I am in the living room when I hear this popping sound, like a string of firecrackers going off out front, along with flashes (and this was in bright sunlight), followed by a hell of a bang. The dogs looked at me like what the heck was that? I look outside and see one of the 13.3 KV lines is severed with some laying in the street going snap, crackle and pop and the remainder dangling from the pictured pole. Within seconds my generator came online so I knew we lost power. God, I love that generator. Anyway, this line is laying in the street smoldering so before any traffic comes along for the first time in my life I dial 911. I also went out in the street to suggest to motorist it may be unwise to hit that line. Police showed first and blocked the street followed by fire department and an EMS squad. Can't say I ever saw our quiet street this busy. Took the power company about an hour to show up. Interesting was about 10 min into all this I was chatting with the cops when my generator shut down. So my guess is all 3 phases dropped offline for a short time. The phase feeding the transformer I am on was not the severed toasted line. Once the power company was onsite they did shut everything down for several hours while they repaired things. We did find small fragments of the balloons which, no kidding, looked to have been vaporized. Really bizarre stuff. The First Energy guys did tell me that line took a lightening strike about a year ago and the insulation was deteriorated which contributed to the situation. Then I found and read this:

https://www.balloonhq.com/faq/deco_rules.html

California actually has laws in place as to metal foil balloons. Some of the reading and stories are pretty good.

Ron

 

There are ways to run a 3-phase motor using phase-shift capacitors from a single phase but the motor efficiency suffers and its maximum power is lower.

This is the principle for RPC's, (Rotary Phase Convertors) Many have been built in the last 30yrs, they mainly have gone out of favour now that VFD's are cheap and prevalent.
Max.

 

There is also no such thing as a 3ph transformer, it is just three single phase transformers mounted on the same frame.
You can create you own with 3 separate 1ph versions.
Max.

 

Looking at it another way,

Each phase supply 1, 2, 3, or 100 is supplied and measured between the phase line and the return line.

If the return line is common to all phases, then consider the effect of connecting a split phase supply to two terminals of a device.
The split phases will always be opposite, resulting in a constant zero output.

A pair of genuine two phase supplies will both drive the device at their appropriate times.

So in this instance I agree with crutschow.

I'm not following what you are saying. If you have, say, 4 phases and all are connected to a common return line, then Phases 1 and 3 are indistinguishable from what we call a split phase supply. As are Phases 2 and 4. Any pair of adjacent phases, say 1 and 2 or 2 and 3, are indistinguishable from what has historically been called a 2-phase supply (namely 90° out of phase).

 

WBahn, firstly there is only one STATOR in a power generator. In Xanadu, I'm sure they can have whatever they wish as far as windings on their STATORS go but they would find it to be very impractical to have a winding or even a single coil per degree of STATOR circumference as I'm sure the output would not be too useful for large scale power generation. May be fun as a novelty to try this.
I am not aware of any 6-phase machines but I guess this would be possible but I don't know of any such system used for large scale power.
Yes, if N=3 as per your post then this would be a 3 phase machine as is used in most power stations and distributed as such.

I'm not talking about having a winding every degree. I'm merely talking about doing it the same basic way that three-phase generators are built, namely by effectively putting three generators on the same shaft with them oriented in such a way that the outputs are 120° out of phase. There is nothing that would prevent this from having two generators on the same shaft but oriented so that they are 90° apart -- this is how the historical two-phase generators were built. There is nothing that would prevent this from having two generators on the same shaft but oriented so that they are 180° apart (or any other phase angle difference you wanted). Why would all of them be properly called a two-phase system and that one special case not? What is the limit at which it is not a two phase system? If they were 179° apart would be 2-phase? And, again, I'm not talking about restricting the terminology to what has developed historically here (hence the use of Xanadu which, presumably, doesn't have our terminological baggage), but rather just sticking to the basic technical concept of what an N-phase system means.

Six-phase systems are used in HVDC installations and experimentally twelve-phase systems have been demonstrated for the purpose of transmitting more power through the same power line corridor than can be done with a three-phase system.

 

WBahn, So what I am picturing from your description is a single long rotating shaft with three windings at 120deg mutual displacement. That would be an interesting design exercise to be able to achieve maximum efficiency and output. I also imagine the excitation magnetic field would have to be spread out over three length along the shaft.
I note that the 2 phase generators quoted seem to have rotating windings and fixed excitation field, with the load being supplied via sliprings.Is that how you would supply load from this imaginary generator.
Modern 3 phase generators have stationary load windings and a rotating exciting winding fed by sliprings. Seems to be a much more effective way of doing it.
I probably would agree with you that what you are describing could be a N-phase system so long as the "peaks" of the voltage occur at some degree of difference with respect to each other as the generator rotates.
However the original question was if the domestic 120/240 supply to US homes was 2 phase and from what I understand I conclude it is not.

 

I'm not talking about some radically new or different design.

Imagine going to a manufacturer of modern generators and you say to them: I want a generator that outputs three phases which are 120° apart (along with other relevant specs such as voltage, current, whatever) and they would say, "We have one of those in the back, where do you want it shipped?" If instead you asked for a generator that outputs six phases that are 60° apart they might say, "That's unusual, but we build a few of them. They are essentially the same as our three-phase units, but it will cost more and will take a while to build." If you went to them and said that you wanted a generator that outputs five phases that are 70° apart except for between the last one and the first one which would be 80°, they would say, "Well, we can make you one of those using the same design concept as the ones we make, but it's a custom job and will cost more and take longer to build. When do you want it and how much are you willing to pay for it?" If you instead asked for a generator that outputs two phases that are 90° apart (and 270° between last and first), they would say the same thing. If you instead asked for a generator that outputs two phases that are 180° apart, are you saying that they would come back and say, "Sorry, that can't be done because it's physically impossible."

 

I'm not talking about some radically new or different design.

Imagine going to a manufacturer of modern generators and you say to them: I want a generator that outputs three phases which are 120° apart (along with other relevant specs such as voltage, current, whatever) and they would say, "We have one of those in the back, where do you want it shipped?" If instead you asked for a generator that outputs six phases that are 60° apart they might say, "That's unusual, but we build a few of them. They are essentially the same as our three-phase units, but it will cost more and will take a while to build." If you went to them and said that you wanted a generator that outputs five phases that are 70° apart except for between the last one and the first one which would be 80°, they would say, "Well, we can make you one of those using the same design concept as the ones we make, but it's a custom job and will cost more and take longer to build. When do you want it and how much are you willing to pay for it?" If you instead asked for a generator that outputs two phases that are 90° apart (and 270° between last and first), they would say the same thing. If you instead asked for a generator that outputs two phases that are 180° apart, are you saying that they would come back and say, "Sorry, that can't be done because it's physically impossible."

Actually, you are very on target. During WWII they (GE) developed a device called an "Amplidyne".

An amplidyne is an electromechanical amplifier invented during World War II by Ernst Alexanderson. It is usually an AC motor driving a DC generator with modifications to increase the power gain available. A small electrical signal can control the position of a large motor using this approach.

The AC motor doesn't have to drive a DC generator. Think of an amplidyne as a large mechanical amplifier. The units I worked with were GE manufacture and used a 40 to 50 horsepower AC motor to drive three generators, their shafts all coupled in a row. Nothing says there must be 3 units. You could have 2 or 4 or 5 or whatever, just string them out. There was no need to align or position the units. The phase relationships were a function of the field excitation. The frequency was also determined by field excitation as was the amplitude out of each unit. The early units during WWII were used to position ship gun turrets. However, later they found other use in the Navy Nuclear Propulsion program. The latter units were the ones I worked with. We had need for AC signals between sub 1 Hz to less than 10 Hz. The early technique was to use a small variable speed Bodine motor to rotate a synchro transmitter. This gave us 3 phase spaced 120 degrees apart. This gives you a small three phase generator with the frequency determined by rotational speed of the synchro. The synchro transmitter had the usual R1 and R2 (Rotor) connections for the rotor and the S1, S2 and S3 outputs for the stator. R1 & R2 were 120 VAC 60 Hz. The output was the 60 Hz. modulated by the rotational speed of the synchro. So if we notch filter the 60 Hz from the output and clean it up we get three nice sine waves spaced 120 degrees apart. Each of those signals was used to drive the fields of three amplidyne units. While all of this was a electro mechanical nightmare it worked real well. We just weren't driving a gun turret with big guns. The units we used could output about 200 volts and 100 amps each. Don't know what they weighed but we used a 10 ton capacity crane to move them. When I retired a few years ago we were still running a few. Over the 20 or so years I worked with them we did advance to much newer and better ways to drive the field windings moving to full computer control designs. The phased out units were being replaced by new inverter designs designed and built by Northrup Grumman Corporation. Really nice stuff. I believe the remaing two that were in service when I left have also since been retired.

So they work pretty much like you describe above but rather than control the phasing relationship by trying to index each unit it's done through field windings. This is a long way from the 120/240 VAC 60Hz delivered to my house.

Ron

 

WBahn, firstly there is only one STATOR in a power generator. In Xanadu, I'm sure they can have whatever they wish as far as windings on their STATORS go but they would find it to be very impractical to have a winding or even a single coil per degree of STATOR circumference as I'm sure the output would not be too useful for large scale power generation. May be fun as a novelty to try this.
I am not aware of any 6-phase machines but I guess this would be possible but I don't know of any such system used for large scale power.
Yes, if N=3 as per your post then this would be a 3 phase machine as is used in most power stations and distributed as such.

I think his point was that if all N windings are 360 apart, then it is all a single phase. The 360 was the key to his example, not the N.

 

Our utility references the 120v/240v service coming to the residence as a single phase service.
It is one phase that comes down to the transformer that will serve approximately 6 homes maximum with the two 120v lines so that you can supply 120v to your 120v appliances from each side of a breaker box. When properly balanced, you are using both sides to service the home.
The reason for 2 x 120v lines is so that your residence can also be supplied with 240v power for your 240v appliances such as the air conditioner unit on your home.
This is all still considered a single phase. The same phase is separated by 180' at the transformer so that you can connect them together at a double breaker in the box to get 240v without that single phase bucking into itself.
A 2 phase system is what the utility company calls a network system. These are two separate phases pulled off of a three phase system. The three phase system is 120' apart, thus 360' with all three phases considered. The two phases used for networking are 120' apart. Thus the voltage for this service is 120v/208v. This is typically found at apartment complexes here in the U.S.
Electric heaters in the apartments will use the 208v. This is how the utility company balances big loads, by using more than one phase at a heavier loaded site(due to the amp draw from electric heaters/multiple dwellings).

Apparently Canada uses 120 degree 2phase for each household as opposed to the single phase 110/220 you correctly described as being used in the US.

 

No, I have no need for three phase service? Actually we have two three phase lines running down my street. We have 13.3 KV and also 25 KV. Now as a side note I know a guy who was out towards the country. His machine shop began small so three phase machines were run off motor/generators (Inverters weren't popular yet). In his case twenty five years ago, as he grew he talked to First Energy about three phase service. To get the nearest 3 phase service and run him 480 Volt 3 Phase his cost would have been around $50,000. The only high voltage line in the area was single phase. As the area grew and three phase got closer the price dropped. Several years ago he finally got the service for about $25,000. Anyway, personally I have no need for it. Had a heck of a pile of 220 Volt single phase motor generators to sell.

Ron

I know a homeowner in the middle of a residential neighborhood who was able to request and get 3-phase to his house. He was an electrician and rewired the panel to suit. He claims his house was far more efficient, but I'm not sure how unless he tore apart his larger motor-driven devices and replaced the motors. Alternatively, he may have been running "220" machines off of two of the phases, which would only supply them with 2-phase 120 at 203 volts. That would make the machines less powerful, but the bill might go down, too.

 

@haygood: Please consider the utility of reviving a thread that died a natural death nearly four years ago.