three phase connection, RMS, uses

Status
Not open for further replies.
MikeMl said:
Even though there may be a 180deg phase difference between L1-N vs L2-N, who cares? Nobody uses it that way!
Click to expand...

But you do admit, don't you, that there is a 180° phase difference--and therefore two distinct phases--between the two sides Despite the fact that nobody calls it 2-phase power. Right? That's all I'm asking for. Sheesh.
 
carbonzit said:
But you do admit, don't you, that there is a 180° phase difference--and therefore two distinct phases--between the two sides Despite the fact that nobody calls it 2-phase power. Right? That's all I'm asking for. Sheesh.
Click to expand...

I admit that there is a 180° phase difference between L1 and L2 with respect to N. I do not regard that as being "two distinct phases". It is a single phase with a center tap.
 
Last edited:
MikeMl said:
Something that would produce a rotating magnetic vector which could be used to apply a torque to the armature of an electric machine.
Click to expand...

I see; you're looking at this from the POV of an electric motor technician. Guess that works.
 
Here is some interesting reading: 2 Phase Power Systems and Two-Phase Electric Solutions

Makes me wonder. Two phase 4 wire; two phase 5 wire and just maybe 120/240 split phase is the same as two phase 3 wire. I just made up the term.

Just like we have 240 2 wire, and 240 3 wire and 240 4 wire single or is it split phase systems.

And gee if I were to connect L1 to the scope channel A input and L2 to scope channel B input, I'd get a phase difference of 180 degrees. Clearly that isn't 90. Maybe 90 degrees defines a two phase power system by definition.

It's SO EASY to get lost in semantics. Who's first matters too.

We talk about males and females everyday and we talk about sexual preferences, but we don't acknowledge SRS surgery, hermapherdytes and shemales and then we find out that some species can reproduce without a mate and some spiders eat their mate after mating. What I'm basically trying to say is that your perception can get really wacked based on your education.
 
KeepItSimpleStupid said:
And gee if I were to connect L1 to the scope channel A input and L2 to scope channel B input, I'd get a phase difference of 180 degrees. Clearly that isn't 90. Maybe 90 degrees defines a two phase power system by definition.
Click to expand...
Yes, 90 degrees does define a two-phase power system. It's the only phase shift in a two-phase system that gives a smoothly rotating magentic field in a motor. (See your reference for mention of this).
 
I offer my genuine thanks to all of you guys. Your replies are very helpful and you all are very nice. I will ask follow-on questions soon.

Best wishes
PG
 
carbonzit said:
Good question. For the answer, just look at your waveform diagram and look at what Phase 2 and Phase 3 are doing when Phase 1 is at its positive peak.

3-phase is pretty strange and wonderful stuff, for such a simple concept ...
Click to expand...

Hi again,

Please have a look these two pictures:

**broken link removed**

**broken link removed**

At "A" point the Phase 1 waveform has an upward direction and is very close to the peak voltage. In other words, at "A" the push is almost maximum. But there should also be an equal pull to suck that 'push' of the electrons (or positive carriers in terms of conventional current) in other two wires. But the problem is that at "B" the Phase 3 waveform is going downward but that pull is not equal to the push in the Phase 1 waveform. So, there should be an additional pull to compensate the push of the Phase 1 waveform. But there is no additional pull available because Phase 2 waveform at "C" also moving upward which is also a push. So, I hope you see the problem here. By the way, points "A", "B", "C" are located under each other. Now please guide me. Thanks a lot.
 
I think you're confused about how to interpret that graph.

You're talking about the directions the waveforms are moving at the point you've selected. That's totally irrelevant to the question you asked. All that matters are the instantaneous values of the waves at that point. So for the point you chose, which is a little before the peak of Phase 1, the opposing forces (the "pulls" as you put it) are the values of Phases 2 and 3 at that point. Doesn't matter which way they're moving; all we're interested in is the value at that point, like a snapshot in time.

If you add together all the pushes and pulls at that one point, they will equal 0.

Remember, "push" and "pull" depend on the position of the wave either above or below the X-axis, respectively, not the direction the waveform is headed.

Typical rookie error. Don't sweat it.
 
Last edited:
How about this to conceptualize. There are three people pulling on a rope to cause a disk to rotate. They are spaced 120 degrees apart. In order for the disk to rotate, someone has to let go a bit. That's the idea of three phase. At all times, the contribution is the same, but the fractional contribution of each varies.
 
I mentioned this before. The graph is just a graph. The sine waves could be voltage or current. However since it is -1 to +1 if you look at where phase A is at the positive peak you will notice that phases B and C are both crossing -.5 so if you add phases B and C you get -1.

Ron
 

Better yet, three people spinning a disk with magical cranks that somehow don't get tangled up with each other. When one person is pushing, the other two are pulling.

Good analogy!
 

Hi carbonzit

Thank you and everyone else.

From my very basic study into calculus I think the slope at A and C is increasing (or positive) but at B is decreasing (or minus), so how are the push and pull equal? Please guide me. Thanks.

Regards
PG
 
Does this attached image help? Note the black arrows. The same is true for any point in time with any phase with respect to the remaining phases but at peaks positive or negative it is much easier to see.

The same relationship would be true of the output of a center tapped transformer. I would have two signals 180 degrees out of phase. As one goes positive the other is equally negative.

Ron
 

Attachments

  • Phases in Time.gif
    21.7 KB · Views: 204
I think when I first really understood 3 phase is when I got into it's generation, in the simplest form, single phase has one winding, 3 phase has 3, each 120 deg apart and depending on how you connect the 3 windings, you have a delta or a Y. Both single and 3 phase have a single rotating field, in it's simplest form. To get a specific frequency (60) a single rotating field spin at 3600 rpm, if you use 2 rotating fields, use 1800 rpm, 3 rotating fields, 1200 rpm, 4 rotating fields, 900 rpm. Each rotating field will have 2 poles, a north and a south, so respectfully you would have a 2 pole generator, a 4 pole, a 6 pole and an 8 pole generator. Single phase has one winding, 3 phase has 3 windings.
Kinarfi
 
PG1995 said:
From my very basic study into calculus I think the slope at A and C is increasing (or positive) but at B is decreasing (or minus), so how are the push and pull equal? Please guide me. Thanks.
Click to expand...

Forget the slope. Slope ain't got nothing to do with it.

It's the instantaneous value of each phase at the selected point on the graph that's important. That's where you add the voltages, and determine that, for the point you selected, the one voltage "pushing" (Phase 1) is exactly balanced by the other two voltages "pulling".

Again: the push or pull is not the slope of the curve at the point; it's simply the Y-value of the curve at that point.

Re-read this a few times if need be. Again, forget slope.
 
Last edited:
Status
Not open for further replies.

Similar threads

V
  • Question
Convert a single-phase motor to a three-phase
Replies
4
Views
1K
ZipZapOuch
  • Question
Converter 0V connection
Replies
5
Views
1K
throbscottle
M
  • Solved
Three legged component
2
Replies
27
Views
3K
MartinTT
M
K
  • Question
Bluetooth Amplifier Board ZK-1002M - Issue with Aux and Bluetooth Connection
Replies
9
Views
2K
KobyCodes
K
S
  • Question
Help wiring a single phase motor
Replies
7
Views
3K
MaxHeadRoom78
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…