Singlephase 240V

[Smart $]

Forgot to add that split phase systems furnished by the POCO are conventionally known as single-phase systems.

What I do have a problem with is systems dubbed single phase that are powered by 208Y/120 3? 4-wire source less one line conductor... but I do understand why such systems are called single phase.

 

[gar]

090907-1202 EST

Larry:

Since there are two ways the secondaries of two transformers or two secondaries of one transformer can be wired in parallel how does your argument above prove that there is only a single phase output?

If the two secondaries are connected such that there is very little circulating current, then the secondaries are in phase. If one pair of terminals are connected together in this case, then there is very little voltage difference between the other two terminals.

If the secondaries are connected the other way, then there is extremely high circulating current because the two waveforms are 180 deg out of phase.

.

 

[Besoeker]

For the rest of us, here's a directly-applicable analogy:

Let's say we take three transformers or a single 3-ph unit, doesn't matter which, with center-tapped-secondaries, and power the primaries the usual way with either wye or delta; it doesn't matter which.

Now, we connect all three secondaries' center taps together, leaving us with a neutral and six hot leads. (This is a great way to feed a rectified power supply, by the way.) Would you call this 3-phase or 6-phase?

It's often called hexaphase. There is some logic in that. Measured phase to neutral (star point), you get six phase shifted voltages at 60deg intervals.

 

[gar]

090907-1534 EST

Phase meters.

http://www.laurels.com/phase.htm?src=google&gclid=CMLryvWr4JwCFWBB5god1WcBKQ
This meter can be set to read +/-180 or 0 to 360.

http://www.gepower.com/prod_serv/pr...ads_new/down_en/test_pro_relays/pam360_en.pdf
Another 0 to 360 range unit.

http://www.powertekuk.com/phasemeter.htm
This instrument is also +/- 180 or 0 to 360. Its noise rejection capability looks quite interesting.

On a single phase center tapped transformer use the transformer center tap and one side of the secondary as the reference, and center tap and the other side as the signal being measured and you will read close to 180.

Thus, clearly one signal is 180 deg out of phase with respect to the other.

.

 

[mivey]

What I do have a problem with is systems dubbed single phase that are powered by 208Y/120 3? 4-wire source less one line conductor... but I do understand why such systems are called single phase.

It is called a 3-wire network service.

 

[Smart $]

It is called a 3-wire network service.

Perhaps...

...and in service notation it is 120/208 1? 3W.

 

[Smart $]

...
Thus, clearly one signal is 180 deg out of phase with respect to the other.

I've not contradicted that fact...

...but the fact alone does not make it a two phase system...

...for every such instance, it can also be said there are two voltage sources having the same phase.

 

[mivey]

Perhaps...

...and in service notation it is 120/208 1? 3W.

I am referring to what it is known in POCO terms for metering.

 

[SG-1]

Smart $, you & I have great POCOs, we are getting polyphase power at single phase prices !! And thanks for the diagram. Obviously, my blondness asserting itself !!

Gar, part of " my definition" of polyphase is that it can be used to derive more phases. Since this particular 2 Phaser system cannot do that, I disqualify it as a polyphase system. I see where it can be called that if by phase you mean branch. I clearly see the two windings are 180 degrees out of phase.

If two phase motors could run using two phases from a three phase system then why a scott connected transformer? My defination of run includes not overheating & losing their magic smoke. Induction motors designed for two-phase operation use the same winding configuration as capacitor start single-phase motors. They need the phase shift to start themselves. Capacitors cause a 90 degree shift.

Gar, I am still waiting for you to "fess up" and say you tried to slip capacitors in. Until then, you are "off" the buddy list.

Mivey,
explain why a center tapped delta is called three phase and not four phase for me.

You seem to be saying a single phase transformer is mis-named.

I think I am going through a "phase" mostly caused by the mist of words.

 

[mivey]

Smart $, you & I have great POCOs, we are getting polyphase power at single phase prices !!

The POCO does not care how many phases you get. POCO rates are based on cost allocations (and politics :roll. Some single phase power costs more than some three-phase power.

Mivey,
explain why a center tapped delta is called three phase and not four phase for me.

In the general definition of a polyphase system, an n-phase system has a 360/n degree displacement between the voltages. A center tapped delta does not fit that definition. Also, a center-tapped delta is a combination of a single-phase and a three-phase system.

You seem to be saying a single phase transformer is mis-named.

I call it single phase. But I also recognize that it can also it fit the definition of a 2-phase system when the general definition of a polyphase system is used.

 

[gar]

090907-2010 EST

SG-1:

This entire thread is about definitions, and the constraints placed on those definitions.

From dictionary.com
http://dictionary.reference.com/browse/polyphase

1. having more than one phase.
2. of or pertaining to a set of alternating currents that have the same frequency but different phases and that enter a specified region at more than two points.

To repeat the same source on phase
http://dictionary.reference.com/browse/phase

1. any of the major appearances or aspects in which a thing of varying modes or conditions manifests itself to the eye or mind.
2. a stage in a process of change or development: Each phase of life brings its own joys.
3. a side, aspect, or point of view: This is only one phase of the question.
4. a state of synchronous operation: to put two mechanisms in phase.
5. Astronomy. a. the particular appearance presented by the moon or a planet at a given time.
b. one of the recurring appearances or states of the moon or a planet in respect to the form, or the absence, of its illuminated disk: the phases of the moon.

6. Zoology. color phase.
7. Chemistry. a mechanically separate, homogeneous part of a heterogeneous system: the solid, liquid, and gaseous phases of a system.
8. Physics. a particular stage or point of advancement in a cycle; the fractional part of the period through which the time has advanced, measured from some arbitrary origin often expressed as an angle (phase angle), the entire period being taken as 360?

The Sola does have a capacitor, but it is still classified as a transformer.

Suppose I create a transformer with two magnetic circuits, one includes a shading coil. Now I can have a transformer with two phase outputs that differ by something other than 0 or 180 deg. This time no capacitor.

I take the approach that one should start with general concepts and then narrow these down with appropriate modifiers.

I can work with a true single phase two wire source. Connect a single phase induction motor to this with no other generated phases while it is running and develop full power per the motor rating. Starting can be done either mechanically or electrically. A two phase motor run on single phase with no excitation to the second phase can still develop a major portion of its rated power. The lost capability is a result the unused coil.

See Bailey and Gault Chapter 16 Single-Phase Motors. See Chapter 17 for Capacitor Motors.

Also note that it is quite common to use a three phase induction motor to create three phase from a single phase source. Not ideal but many are in use.

.

 

[mivey]

This entire thread is about definitions, and the constraints placed on those definitions.

And I think that is what is causing some problems. Because of past definitions, some cannot tie to a general definition. I have been using a general definition of uniformly spaced phases. You have given examples of a general definition covering non-uniformly spaced phases. I don't think either of us have a problem when these definitions cross each other. Others just can't seem to make the connection. Perhaps some time spent in the audio world would broaden their minds.

The 90-degree system originally labeled as 2-phase was two single phase systems with a distinct relationship. This system could also be considered part of a 4-phase system. Some of those having problems broadening their mind could probably walk the path from the historic 2-phase system to a 4-phase system (and would almost be forced to).

But at what point do you take the 4-phase system with four 90-degree relationships and turn them into two 180 degree relationships and call it 2-phase? It appears that is what some say you have to do by saying that even-numbered systems can't exist.

I like your example of walking the degree circle that illustrates that at some point you might run into your definition.

I guess if we in the U.S. electric world generally deem 2-phase as having a 90-degree phase displacement, the rest of the electric world, audio world, circuit world, and other disciplines need to fall in line. :roll:

I'm all for using standard terminology, but we should not lose sight of the bigger picture. Many want to use a historic label as an all-encompassing definition. Most definitions are not that absolute.

 

[LarryFine]

Thus, clearly one signal is 180 deg out of phase with respect to the other.

Yes, but it's a factor of polarity, not a timing factor. I say that, while it resembles, or behaves, as out of phase, it really isn't. That the opposing peaks occur simultaneously keeps it from being polyphase.

 

[mivey]

Yes, but it's a factor of polarity, not a timing factor. I say that, while it resembles, or behaves, as out of phase, it really isn't. That the opposing peaks occur simultaneously keeps it from being polyphase.

Why do you think timing is a factor?

The timing is really not relevant past the first 1/2 cycle and really only matters in the audio (or similar) world. We are not talking about a delayed signal anyway.

Two separate but opposite signals will peak simultaneously but that does not mean it is only a matter of polarity. In this case, it just so happens that a polarity change and a 180 degree difference are the same thing (again, we are not talking about time delays).

 

[SG-1]

In the general definition of a polyphase system, an n-phase system has a 360/n degree displacement between the voltages. A center tapped delta does not fit that definition. Also, a center-tapped delta is a combination of a single-phase and a three-phase system.I call it single phase. But I also recognize that it can also it fit the definition of a 2-phase system when the general definition of a polyphase system is used.

I am having a little trouble with this quote thingy, can you tell ?

mivey,
I think I see your point & the definition here. I have been over-reading (looking) the definition. You are stating that if I substitute 2 for n above, the system has a 360/2 = 180 degree displacement. This satifies the general definition for a polyphase system. Sorry that took over-long to sink in.

Now that I see this, you call it single phase too.

 

[mivey]

Now that I see this, you call it single phase too.

I call it single phase because that is what most everybody in the U.S. that I work with in the electrician world and the POCO world calls it.

I understand what the ones who call it two phase are talking about. Some are strictly going by a "hot wire" count and some are bringing in terms from other disciplines. Not a problem. I can see where they are coming from.

Some of our own (U.S.) references acknowledge that there is a technicality. Because of this, it never hurts to be aware of the technical reasons you could call it either way, regardless of what common practice dictates.

From what I've read, I think it may be different outside the U.S. and even have a reference book from Cambridge that uses the 2-phase terminology.

 

[SG-1]

090907-2010 EST

The Sola does have a capacitor, but it is still classified as a transformer.

.

The Sola is one of my favorite transformers.

Do not worry about my buddy list. I never had one to take anybody off
Besides, I was not finished digging information out of you yet. :grin:

 

[SG-1]

mivey, did I get ? Have I learned something new ?

 

[mivey]

mivey, did I get ? Have I learned something new ?

Yes, you got the 360/n definition: it does not hinge on the number of conductors/wires, but on the characteristics of the system.

The definition Gar used has a similar hinge point.

Now that you know why you COULD call it 2-phase, know that it is best NOT to call it 2-phase in our application, at least for our little slice of the world. It could be technically correct from a general standpoint, but not a common use of the term for our world.

 

[Smart $]

...

The Sola does have a capacitor, but it is still classified as a transformer.

...

Actually, SolaHD classifies it as a power conditioner... it is of the transformer category because that is the major voltage derivation component.

http://www.solaheviduty.com/products/powerconditioning/cvs.htm