Is it Single or Two Phase?

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Thanks Matt.

As for your second question, can you say "hijack"? ;)

The phase shift in magnetic circuits will complicate this thread.

You aren't by chance around the Ames area?
 
Al,
Thanks for jumping in explaining this. Two people will explain the same thing using different language, often to the help of people trying to understand the issues.

Dave,
I'll work on some drawings later.

-Jon
 
You can't stop now.......

You can't stop now.......

Jon,

Please don't bother with the drawings!

Please do reply to the other questions I have asked about your claims. Quite honestly, they are a little far fetched. Please help us understand your take on AC theory as it does not seem to line up with any I am familiar with.

Thanks,
 
Four phase:

Four phase:

Now to muddy the waters, there is, or was, such a thing as a four-phase sytem. In this case the phase angles would be 0, -90, -180, -270.

In this case, the "extra" phases can be obtained from center tapped secondaries. But 120/240V service is still single phase!

You can have a four-phase star, or a four-phase mesh. Think about it.
 
Rattus,

How can you tell the difference between what you're describing as four phase, and a five wire two phase star?
 
Ahhhhha!

Ahhhhha!

Please, lets get some of this stuff accurate!

You can NOT simply center tap a phase coil and derive a new phase. This is simply not true! Phases are created at the point of generation or derived with further coils tapped from existing phases. I have never seen more phases added than the number of phases originally generated.

Now, please, please, correct me if I am wrong! Let's end the claims with NO documentation. It only discredits our industry as a whole and causes distrust among it's members.
 
al hildenbrand said:
Rattus,

How can you tell the difference between what you're describing as four phase, and a five wire two phase star?
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Al, I believe they are the same thing.

The star would comprise two center tapped secondaries with the CTs connected to form a neutral.
 
websparky said:
Please, lets get some of this stuff accurate!

You can NOT simply center tap a phase coil and derive a new phase. This is simply not true! Phases are created at the point of generation or derived with further coils tapped from existing phases. I have never seen more phases added than the number of phases originally generated.

Now, please, please, correct me if I am wrong! Let's end the claims with NO documentation. It only discredits our industry as a whole and causes distrust among it's members.
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Dave, in the special case of a four-phase system, two of the phases can be derived from center tapped xfrmrs. Think about the system described by Al.

If I present four phases from a black box, you cannot tell whether phases 3 and 4 are generated separately or derived from a center tapped transformer.

For that matter, you could make a six-phase system from three phases with center tapped windings.

But, the ubiquitous 120/240V service is single phase.
 
More phases:

More phases:

I think the key point is that in a single phase system, the second leg, being 180 degrees our of phase from the first, is of no benefit.

In a two phase system, the second leg is 90 degrees from the first, and this is beneficial in the operation of motors.

Adding two more phases would be even more beneficial.

If the extra leg, however derived, is beneficial, we can call it a phase.
 
winnie said:
...

Smart $, I see... you are... inciteful but slightly wrong.

...
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Thank you for the wonderful explanation. Much, much better than "You are wrong" without substantiation that I was getting from others. I believe some meant well. For those that are dying to here me say I was wrong, I admit I was in error... (the catch) ...but only about there being a phase-angle difference between the center tap and the ends of the winding it taps. Yes it confused the issue, not to mention me in trying to prove myself wrong, and all the while getting bombarded with other shall we say colorful, and uninformative responses. After getting away from them for awhile has me thinking a lot clearer.

winnie said:
...

I think this 'relativity' issue is the point that you were making by discussing phase angles changing with grounding; the phase angles of the actual system relative to itself _will not change_, but the phases of the terminals as measured relative to a ground reference will clearly change because you are changing the reference.
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re: "...will clearly change because you are changing the reference"... I once posted a similar remark about reference point in a discussion you were having on electrons moving right and "holes" moving left. The reference point appeared to have evaded you on that issue much the same as it was evading me on this issue. That darn reference point sure can be a shifty li'l bugger :D

Anyway, a majority of the discussion here resulted from my stating 240/120 1? off a center-tapped delta is a two-phase system. As you and others have read, that statement has met with quite the opposition. I believe the discord IS a matter of "relativity", that being whether you are looking at the system from the utilization end or the generation end. The discussion has definitely "beat the dead horse" from the utilization perspective (albeit one "reality"), but my claim that it is a two-phase system is solely from the generation view. I think no one person can deny that the branch system derives its single phase power from two distinctly generated phases having a temporal displacement of the sinusoidal waveform as referenced to the generation end. Even the original, old-timer Two Phase utilized single phase power for single phase equipment.

View attachment 56
 
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websparky said:
Please, lets get some of this stuff accurate!

You can NOT simply center tap a phase coil and derive a new phase. This is simply not true! Phases are created at the point of generation or derived with further coils tapped from existing phases. I have never seen more phases added than the number of phases originally generated.

Now, please, please, correct me if I am wrong! Let's end the claims with NO documentation. It only discredits our industry as a whole and causes distrust among it's members.
Click to expand...
The point here is, yes you can "derive a new phase" but it is not a generated phase... and it is only a derived phase with respect to any point not on the same winding. Take center-tapped delta for example, if the center tap is on the A-C winding, the center-tap to B terminal has a waveform that is 90? out of phase with A-tap-C...

[EDIT]As I recall, you even posted a link to wikipedia topic of Scott-T Transformer, which uses this very principle to generate..er--rr-r.. derive a two-phase output...[END EDIT]
 
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Smart $ said:
View attachment 56
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Just to point it out, notice that your own attachment shows that, even with four "phases" (hot wires) shown, the drawing refers to it as two phase power. The point is that adding a center tap doesn't create an additional "phase". ;)
 
180 degrees out of phase?

180 degrees out of phase?

rattus said:
I think the key point is that in a single phase system, the second leg, being 180 degrees our of phase from the first, is of no benefit.

In a two phase system, the second leg is 90 degrees from the first, and this is beneficial in the operation of motors.

Adding two more phases would be even more beneficial.

If the extra leg, however derived, is beneficial, we can call it a phase.
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I still do not get this. I dont see how the phases are ever 180 deg out of phase, they can only be 120 deg right?

With the delta secondary, you are center tapping a single winding, which does not change the phasing, but it does change the way the magnitude of voltage adds, thus 240 V.

-Matt
 
Semantics:

Semantics:

LarryFine said:
Just to point it out, notice that your own attachment shows that, even with four "phases" (hot wires) shown, the drawing refers to it as two phase power. The point is that adding a center tap doesn't create an additional "phase". ;)
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Larry, my book says that a two-phase system and four-phase system differ only in their internal connections. Clearly there are four phase angles in the system shown by Smart. Strictly speaking, it is a four-phase system.

Be that as it may, I see no advantage to the five-wire system. Two-phase motors undoubtedly achieve an effective phase reversal internally and can run just fine with three wires if they are wired to do so.
 
mpross said:
With the delta secondary, you are center tapping a single winding, which does not change the phasing, but it does change the way the magnitude of voltage adds, thus 240 V.
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The magnitude of the voltage, phase to phase, is the result of the transformer turns ratio, or, lacking a transformer and having a direct connection to the output of a utilization voltage generator, the generated voltage of the windings inside the generator.

Matt,

The center tap on one side of a 4 wire delta, especially a grounded center tap, is a red herring with respect to the "center" of the phasors that describe the voltage on the A, B & C phase legs.

Winnie (Jon) has it right by bringing up the "virtual neutral" as the reference for the phasors on the A, B & C legs. Even though this seems to be "getting" Dave.

Center tap or no, on a 240 V delta, if I measure the voltage with my two probe voltmeter between the center tap of a (any of the 3 windings) over to either end of that same winding, I will measure 120 V.

--Edit typo, Al--
 
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mpross said:
I still do not get this. I dont see how the phases are ever 180 deg out of phase, they can only be 120 deg right?

With the delta secondary, you are center tapping a single winding, which does not change the phasing, but it does change the way the magnitude of voltage adds, thus 240 V.

-Matt
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Matt, you have pulled ONE phase from the transformer. You no longer have a three-phase system. Va, Vb, and Vc are separated by 120 degrees, but since you only have Va for example, you can no longer reference Vb and Vc.

V1 and V2 add to 240V because the phase angle is 180 degrees. If the angle were 120 degrees, they would add to 208V.

If you look at L1 and L2 relative to the neutral, you will see a separation of 8.33 milliseconds--half a cycle, 180 degrees.
 
rattus said:
I see no advantage to the five-wire system. Two-phase motors undoubtedly achieve an effective phase reversal internally and can run just fine with three wires if they are wired to do so.
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The advantage I see is that I can take 120/240 V center tapped 3 wire SINGLE PHASE off of any two opposing phase legs.

This is similar to a 4 wire 120/240 volt delta with its dual 1? / 3? use, except that the 5 wire two phase source permits TWO separate 3 wire single ? sources.

And, second, just to pick on a term, "effective phase reversal", I would say something like "rotating magnetic field".
 
After a little more reflection, consider 240 V 3 wire corner grounded Delta. Let's say the grounded corner is the "B" phase.

The Voltage from A and C phases to ground (and the B phase) is 240 volts. . . The B phase zero volts, however, has a PHASE ANGLE.

The B phase zero volt phase angle is referenced to the "virtual neutral" that Winnie describes earlier.

. . . .

Now, back to the 240 V 4 wire Delta with a grounded center tap "neutral".


The zero voltage on the grounded conductor of a 240 V 4 wire Delta has a PHASE ANGLE when referenced to the to the SAME "virtual neutral" that the A, B & C phases are referenced from.

--Edit, Sorry, my son distracted me. Clarified text. Al--
 
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I have watched the debate go back and forth regarding the voltage angle between lines L1 and L2 on a 120/240V system. (I have purposely not mentioned phases, damn, I just did!)

Anyway, has it FINALLY been accepted that they are 180 deg apart? "If so, let's put that to bed and just stick with the phase issue ( A-rrr, did it again!) Phase, phase, phase, when will it ever end?
 
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