240V Open Delta

[mivey]

We have the same argument during our "is a center-tapped secondary two phases?" discussions. :roll:

Moving beyong that, look at a case that is harder for you to ignore: Why would you say that a 3-wire system with a 90? displacement can be called 2-phase but if you add another 30? of separation that it suddenly can only be called single-phase. Don't you see the discontinuity in that logic?

That is why the historic names are not a universal fit for every case and we can't derive a generalized set of naming conventions based on those historic names. Rather, the historic names were derived to fit a specific sub-set of the general case.

 

[mivey]

There must be three primary conductors, one of which may be the neutral.

I agree with that as well. The difference being that with the neutral, I call that 2-phase. You are calling it 3-phase. Jim calls it single-phase.

 

[mivey]

That's the exact same scenario as two lines and the neutral from a 208Y/120v source.

It is the same voltage configuration. Historically calling it single-phase is because the loads are single-phase. I don't have a big issue with that as long as people recognize where the name came from.

In the utility industry, we call the 120/208 a network service. I suspect it is to distinguish it from a 120/240 type service. The primary of this type we commonly call 2-phase.

 

[mivey]

To be more precise, we can say that the open delta uses two phases of a three phase distribution system. It is unlikely that the power plant generates only two phases.

That's true. But that is not to say it couldn't. I have a circuit that generates a 3-phase source using a single input wave. This is done by cascading the wave through delay stages. If I had no use for the third phase, I could easily leave the last stage unconnected and have a 2-phase supply.

Naturally, that is not done in the utility industry because 3-phase is much more efficient. But we do run many sections of 2-phase distribution.

 

[rattus]

That's true. But that is not to say it couldn't. I have a circuit that generates a 3-phase source using a single input wave. This is done by cascading the wave through delay stages. If I had no use for the third phase, I could easily leave the last stage unconnected and have a 2-phase supply.

Naturally, that is not done in the utility industry because 3-phase is much more efficient. But we do run many sections of 2-phase distribution.

Or, we could have a pair of PE-75 hand cranked generators coupled through a timing belt? We would need a pair of guys to pull the ropes at the same time!! Or maybe we could use one extra strong guy to pull both ropes.

 

[mivey]

My reference materials, well at least the ones on my desk right now, (UGLY's, ANSI/IEEE C57.105, and Cooper Power Systems R201-90-2) all call the feed, to open-delta and open-wye transformer connections, as 3-phase.

Maybe you are trying to interpret something they are not really saying. From Cooper Power System's "Electrical Distribution System Protection" manual after listing the various type of 3-phase systems:

Additional classifications of circuits involving various combinations of one or two phase conductors and a neutral could be identified, but these exist in practice only as two-phase or single-phase laterals tapped off of one of the above systems. So single- or two-phase laterals are not described here as separate types of distribution circuits, but rather are referred to in terms of the type of circuit from which they are supplied

 

[mivey]

Or, we could have a pair of PE-75 hand cranked generators coupled through a timing belt? We would need a pair of guys to pull the ropes at the same time!! Or maybe we could use one extra strong guy to pull both ropes.

I remember a demo the EMC had one time where you rode a bike to power some lights. The idea was to make people think of electricity as relatively cheap. It was a good demo.

I remember one time a citizen complaining about water rates. The mayor told him he could bring one 5-gallon bucket of water per trip to his house, as many times as he wanted, and he would give him all the water he wanted for free. The guy decided that water coming right out of his sink faucet was relatively cheap after all.

 

[LarryFine]

Jim refuses to acknowledge that 2 hot conductors and a neutral, or common, conductor is also called 2-phase by a large section of the industry.

Because it is common in the utility industry (my current field).

The source has three, equal-magnitude, phase-displaced voltages so it would normally be labeled as a 3-phase source.

If the load uses the voltage Vba AND Vac (or any other combination of two equal magnitude, phase-displaced voltages), then it is a two-phase load and I am using the source as a two-phase supply.

By common utility language, the feed to open-delta would be 3-phase and the feed to the open-wye would be 2-phase.

For all of this, we "LV'ers" would use the term "two phases" rather than "two phase." You're right: we save "two phase" for the antiquated 90-degree supply.

The difference being that with the neutral, I call that 2-phase. You are calling it 3-phase. Jim calls it single-phase.

Unless we're making an open-Delta of our own, we don't use poly-phase from two lines and the neutral; we're either supplying 120v 1ph or 208v 1ph.

The only time we might use two phases and the neutral, and preserve the 3-ph characteristics, would be using two buck-boosts. Even then, though, we'd never refer to it as "two-phase."

It is the same voltage configuration. Historically calling it single-phase is because the loads are single-phase. I don't have a big issue with that as long as people recognize where the name came from.

Interestingly, we seem to be arguing the same point from the opposite sides: we don't want to use "two-phase" because the source is three-phase, and you do want to for the same reason.

In the utility industry, we call the 120/208 a network service. I suspect it is to distinguish it from a 120/240 type service. The primary of this type we commonly call 2-phase.

Again, since we don't usually supply a single load with 120/208v (major appliances in apartments aside), we have no reason to care about the timing difference, whereas you use it. The open Delta is the perfect example.

I have a circuit that generates a 3-phase source using a single input wave. This is done by cascading the wave through delay stages. If I had no use for the third phase, I could easily leave the last stage unconnected and have a 2-phase supply.

One would have to ask: what would be the voltage and timing difference between the phases? (Well, this one would. :grin

Naturally, that is not done in the utility industry because 3-phase is much more efficient. But we do run many sections of 2-phase distribution.

Two phases.

 

[LarryFine]

The guy decided that water coming right out of his sink faucet was relatively cheap after all.

He learned the delivery is more valuable than the substance.

Now, if we could just get customers to grasp that concept. :roll:

 

[mivey]

You're right: we save "two phase" for the antiquated 90-degree supply.

And when dealing with LV stuff, I avoid that name when it might cause confusion. In the EC world, "2-phase" invokes the thought of the 90? displaced system. That does not mean an EC would not be better off to understand the general relationships among the voltages rather than saying "nothing else but 90? is two-phase". Yeah, other stuff is also two-phase, but we tend to stick with the historic names. Again, I think it is better to understand why the names fit the specific cases they are glued to.

Again, since we don't usually supply a single load with 120/208v (major appliances in apartments aside), we have no reason to care about the timing difference, whereas you use it. The open Delta is the perfect example.

And in the majority world we deal with, there is no difference in a timing difference, phase shift, or polarity change, as the steady-state conditions are exactly the same.

One would have to ask: what would be the voltage and timing difference between the phases? (Well, this one would. :grin

The voltages are sinusoidal and have the same magnitude but are delayed by 0.00556 seconds (or shifted by 120?). Actually, it is not exactly 120?, but close enough for me to play around with.

Two phases.

Semantics.

 

[LarryFine]

Semantics.

Exactamundo!

 

[Sierrasparky]

Are you talking about SWER?

Never heard the term SWER.
What I have seen is only a single wire on the utility pole, to a transformer then to a ground wire rinning down the pole to a ground rod. Then the secondary is an ordinary 120/240v triplex. I have never seen this is southern Calif. Always two phase conductors for the primary to a 120/240v secondary.

 

[LarryFine]

What I have seen is only a single wire on the utility pole, to a transformer then to a ground wire rinning down the pole to a ground rod.

That's it: Single Wire, Earth Return.

 

[jim dungar]

Maybe you are trying to interpret something they are not really saying. From Cooper Power System's "Electrical Distribution System Protection" manual after listing the various type of 3-phase systems
Quote:
Additional classifications of circuits involving various combinations of one or two phase conductors and a neutral could be identified, but these exist in practice only as two-phase or single-phase laterals tapped off of one of the above systems. So single- or two-phase laterals are not described here as separate types of distribution circuits, but rather are referred to in terms of the type of circuit from which they are supplied

You need to use all of the words in a description to get the true meaning.
Cooper is not saying 2-phase, they are saying two phase conductors and two phase laterals. In their literature the word phase is being used as an adjective not a noun.

 

[Cmdr_Suds]

I have always liked the term "split phase" when refering to 120/240 service. I felt it more accuractly discribed what was going on.

 

[mivey]

You need to use all of the words in a description to get the true meaning.
Cooper is not saying 2-phase, they are saying two phase conductors and two phase laterals. In their literature the word phase is being used as an adjective not a noun.

It might be a fun exercise to re-write another's literature because we do not like the way they said it, or we do not think they said what we think they should have said. In fact, there is a thread about that very thing: http://forums.mikeholt.com/showthread.php?t=126834

However, the authors in this case were perfectly capable of saying "two phase conductors" when they wanted to and saying "two-phase" when they wanted to and, in fact, they did. In the spirit of getting to the "true meaning" however, why don't we investigate what it means to call a wire a "phase"?

When looking at the "phases" we are really talking about the voltages (voltage waveforms). If we have voltages (sinusoidal for us) that peak at different times, we say they have a difference in phase. Because they have a difference in phase, we have traditionally labeled these voltages as "phases".

Brief history: Counting phases in a system:

When we group voltages into different systems, we group those that have significantly the same magnitude. We have 120 volt systems, 240 volt systems, 208 volt systems, 277 volt systems, etc. Inside the system group, we create sub-groups of voltages that have the same phase angle in order to separate the voltages into unique sub-groups. The number of sub-groups determines the highest phase order (# of phases) of the system.

That does not mean the voltages have to be used by loads of that same order, and many times they are not. Often, the load type might determine the name we use for our group of voltages. Regardless of the traditional name used for the system of voltages, the physics of the voltages remains the same. For example, we could have three (3) single-phase-voltage systems or one (1) three-phase system. We even have supplies that have a mixture of different systems.

If the unique voltages are evenly displaced with phase angles that sum to 360 degrees, the system is said to be a regular system, like a 3-phase wye or delta. Otherwise, the system is said to be an irregular system, like the 90-degree displaced 2-phase system of old (also known as a quarter-phase system).

There is a particularly interesting regular system, and that is the system with two voltages displaced by 180 degrees. These voltages are exactly those of the center-tapped 3-wire single-phase system and, as such, represent a single-phase system. That is why we call it single-phase instead of two-phase. But one should not forget the twofold nature of this system; a fact that is not over-looked when the 3-wire single-phase system is grouped with multiphase systems when studying the application of the method of symmetrical components, where it is actually assigned a characteristic angle of 180 degrees (see Wagner/Evans "Symmetrical Components" 1933).

Here is another quote on the matter:

From "Engineering Circuit Analysis" by William Hayt, 1962:
The name single phase arises because the voltages Ean and Enb, being equal, must have the same phase angle. From another viewpoint however, the voltages between the outer wires and the central wire, which is usually referred to as the neutral, are exactly 180? out of phase. That is, Ean = -Ebn and Ean + Ebn = 0. In a following section we shall see that balanced polyphase systems are characterized by possessing a set of voltages of equal magnitude whose (phasor) sum is zero. From this viewpoint, then, the single-phase three-wire system is really a balanced two-phase system. "two-phase", however, is a term that is traditionally reserved for something quite different, as we shall see in the following section.

So what does all that mean for the wires? It depends on if the source voltages (EMFs) are in a wye or delta configuration. With a delta configuration, the phase voltages are the line-to-line voltages (commonly called the "line" voltage). In the delta case, the "line" voltage and "phase" voltage is the same. In a wye configuration, the phase voltages are the line-to-neutral/common voltages. In the wye case, the "line" voltage is equal to sqrt(3) times the "phase" voltage.

So how about the utility distribution? For the delta case (no neutral available), bringing out two wires results in a single-phase system (one line-line voltage). Bringing out three wires results in a three-phase system (there are three line-line voltages, even if we have a one missing transformer coil). There is no two-phase case because we have no neutral. Jim's line-line voltage phase-counting method works great for this because the line-line voltages are the original "phase" voltages.

For the wye case (neutral/common available), bringing out two wires results in a single-phase system (one line-line voltage or one line-common voltage). Bringing out three wires could result in a three-phase system (three line-line voltages) or a two-phase system (two line-neutral voltages). The line-neutral voltages are the original "phase" voltages. Of course, bringing out four lines is a three-phase system (three line-line voltages or three line-neutral voltages).

Jim's method does not work too well for a wye system. If you insist on line-line voltages being the phase count, you get one phase for two lines + the neutral (one line-to-line voltage). The problem is you get zero phases for one line + the neutral as you have no line-line voltage. The problem is that the method ignores the fact that the line-to-neutral voltages are the "phase" voltages in a wye system.

Jim's method also does not work well for the quarter-phase system because there are four line-line voltages in the 5-wire 2-phase system (the truth of the matter is that the 3-wire quarter-phase system is a sub-set of a 4-phase system).

All that to say: There are two phase voltages in a wye system that has two ungrounded conductors plus the neutral. As such, it can be called a two-phase system using the general definition for poly-phase systems.

 

[mivey]

It might be a fun exercise to re-write another's literature because we do not like the way they said it, or we do not think they said what we think they should have said. In fact, there is a thread about that very thing: http://forums.mikeholt.com/showthread.php?t=126834

However, the authors in this case were perfectly capable of saying "two phase conductors" when they wanted to and saying "two-phase" when they wanted to and, in fact, they did. In the spirit of getting to the "true meaning" however, why don't we investigate what it means to call a wire a "phase"?

When looking at the "phases" we are really talking about the voltages (voltage waveforms). If we have voltages (sinusoidal for us) that peak at different times, we say they have a difference in phase. Because they have a difference in phase, we have traditionally labeled these voltages as "phases".

Brief history: Counting phases in a system:

When we group voltages into different systems, we group those that have significantly the same magnitude. We have 120 volt systems, 240 volt systems, 208 volt systems, 277 volt systems, etc. Inside the system group, we create sub-groups of voltages that have the same phase angle in order to separate the voltages into unique sub-groups. The number of sub-groups determines the highest phase order (# of phases) of the system.

That does not mean the voltages have to be used by loads of that same order, and many times they are not. Often, the load type might determine the name we use for our group of voltages. Regardless of the traditional name used for the system of voltages, the physics of the voltages remains the same. For example, we could have three (3) single-phase-voltage systems or one (1) three-phase system. We even have supplies that have a mixture of different systems.

If the unique voltages are evenly displaced with phase angles that sum to 360 degrees, the system is said to be a regular system, like a 3-phase wye or delta. Otherwise, the system is said to be an irregular system, like the 90-degree displaced 2-phase system of old (also known as a quarter-phase system).

There is a particularly interesting regular system, and that is the system with two voltages displaced by 180 degrees. These voltages are exactly those of the center-tapped 3-wire single-phase system and, as such, represent a single-phase system. That is why we call it single-phase instead of two-phase. But one should not forget the twofold nature of this system; a fact that is not over-looked when the 3-wire single-phase system is grouped with multiphase systems when studying the application of the method of symmetrical components, where it is actually assigned a characteristic angle of 180 degrees (see Wagner/Evans "Symmetrical Components" 1933).

Here is another quote on the matter:

From "Engineering Circuit Analysis" by William Hayt, 1962:
The name single phase arises because the voltages Ean and Enb, being equal, must have the same phase angle. From another viewpoint however, the voltages between the outer wires and the central wire, which is usually referred to as the neutral, are exactly 180? out of phase. That is, Ean = -Ebn and Ean + Ebn = 0. In a following section we shall see that balanced polyphase systems are characterized by possessing a set of voltages of equal magnitude whose (phasor) sum is zero. From this viewpoint, then, the single-phase three-wire system is really a balanced two-phase system. "two-phase", however, is a term that is traditionally reserved for something quite different, as we shall see in the following section.

So what does all that mean for the wires? It depends on if the source voltages (EMFs) are in a wye or delta configuration. With a delta configuration, the phase voltages are the line-to-line voltages (commonly called the "line" voltage). In the delta case, the "line" voltage and "phase" voltage is the same. In a wye configuration, the phase voltages are the line-to-neutral/common voltages. In the wye case, the "line" voltage is equal to sqrt(3) times the "phase" voltage.

So how about the utility distribution? For the delta case (no neutral available), bringing out two wires results in a single-phase system (one line-line voltage). Bringing out three wires results in a three-phase system (there are three line-line voltages, even if we have a one missing transformer coil). There is no two-phase case because we have no neutral. Jim's line-line voltage phase-counting method works great for this because the line-line voltages are the original "phase" voltages.

For the wye case (neutral/common available), bringing out two wires results in a single-phase system (one line-line voltage or one line-common voltage). Bringing out three wires could result in a three-phase system (three line-line voltages) or a two-phase system (two line-neutral voltages). The line-neutral voltages are the original "phase" voltages. Of course, bringing out four lines is a three-phase system (three line-line voltages or three line-neutral voltages).

Jim's method does not work too well for a wye system. If you insist on line-line voltages being the phase count, you get one phase for two lines + the neutral (one line-to-line voltage). The problem is you get zero phases for one line + the neutral as you have no line-line voltage. The problem is that the method ignores the fact that the line-to-neutral voltages are the "phase" voltages in a wye system.

Jim's method also does not work well for the quarter-phase system because there are four line-line voltages in the 5-wire 2-phase system (the truth of the matter is that the 3-wire quarter-phase system is a sub-set of a 4-phase system).

All that to say: There are two phase voltages in a wye system that has two ungrounded conductors plus the neutral. As such, it can be called a two-phase system using the general definition for poly-phase systems.

Strange. This post did not show up in my "today" list. I was just making another post as a test. I read another thread about one of Al's threads having issues. Anyway, back to our regularly-scheduled programming.

 

[mivey]

You need to use all of the words in a description to get the true meaning.
Cooper is not saying 2-phase, they are saying two phase conductors and two phase laterals. In their literature the word phase is being used as an adjective not a noun.

They are saying 2-phase as in phases, not just a piece of wire. A phase is a voltage and the reference is to the phase voltages, not just the conductors used.

Here is another piece of literature ("Distribution System Modeling and Analysis", William H. Kersting) from another industry expert that calls it two-phase as well:

A typical distribution system will be composed of one or more distribution substations consisting of one or more feeders. Components of the feeder may consist of the following: ... Three-phase, two-phase (?V? phase), and single-phase laterals ... Three-phase, two-phase, and single-phase loads

 

[jim dungar]

They are saying 2-phase as in phases, not just a piece of wire. A phase is a voltage.

A phase is a voltage? Where did you get that definition.

Here is another piece of literature ("Distribution System Modeling and Analysis", William H. Kersting) from another industry expert that calls it two-phase as well:

I see him saying three-'phase laterals', two-'phase laterals', and single-'phase laterals'. I guess I read 'commas in series' different than you do.

 

[mivey]

A phase is a voltage? Where did you get that definition.

There are many references, but it is intuitive when you really think about what it means to have "a phase". The "phase" is a source (at least for what we are discussing). The older term used was "emf" but that is hardly used any more as the term voltage has become more prevalent. EMF is still used at times to emphasize the difference between a source voltage and a voltage drop in a circuit.

Also, we could consider different phases from current sources (you will find that in older literature), but in our discussion of power distribution we are talking about voltage sources. Voltage sources are what we use to classify an n-phase system. There are oodles of references for this info but here are a couple:

"Electric Machinery", Fitzgerald/Kingsley:

Generation, transmission, and heavy-power utilization of ac electric energy almost invariably involve a type of system or circuit called a polyphase system or polyphase circuit. In such a system, each voltage source consists of a group of voltages having related magnitudes and phase angles. Thus, an n-phase system employs voltage sources which typically consist of n voltages substantially equal in magnitude and successively displaced by a phase angle of 360?/n. A three-phase system employs voltage sources which conventionally consist of three voltages substantially equal in magnitude and displaced by phase angles of 120?

"Techniques of circuit analysis", Carter/Richardson:

A three-phase voltage source consists of three voltages sources having equal magnitudes but phase differences of 120 degrees between them, and connected in a symmetrical manner. The two possible modes of connexion are the star-connexion (fig. 3.13(a)) and the delta-connexion (fig. 3.13(b))... In practice the three sources are combined in a single device, and are described as its phases.

I see him saying three-'phase laterals', two-'phase laterals', and single-'phase laterals'. I guess I read 'commas in series' different than you do.

You must. I guess it is just a matter or perspective. Here is some different work from the same author (better nitro-up before you read this one):

"Center-Tapped Transformer and 120-/240-V Secondary Models" William H. Kersting:

Distribution engineers have treated the standard ?single-phase? distribution transformer connection as single phase because, from the primary side of the transformer, these connections are single phase and, in the case of standard rural distribution, single phase line to ground. However, with the advent of detailed circuit modeling, we are beginning to see distribution modeling and analysis being accomplished past the transformer to the secondary, which now brings into focus the reality that standard 120-/240-V secondary systems are not single-phase line-to-ground systems, but they are three-wire systems with two phases and one ground wire. Furthermore, the standard 120-/240-V secondary system is different from the two-phase primary system in that the secondary phases are separated by 180? instead of three phases separated by 120?.