May I ask a question about the single vs two phase stuff

[ggunn]

Has anybody posted vector diagrams? If not, wouldn't that be prudent to the discussion.

You'd just have two arrows sticking out in opposite directions, and you'd still have people arguing whether the second arrow got there by rotation about the center point or going back through the center to the other side.

 

[jaggedben]

Still looking for dialogue on what would be different with distorted waveform on true 180 vs -1.

-1 would better approximate reality a.k.a. what you'd see on the scope. See post 241.

 

[Ingenieur]

if mivey's detailed and science based arguements have not made it clear:
there are 2 distinct phases
and they are independant, ie, the load on one does not impact the other
nothing will

 

[Ingenieur]

Which means that it's the "way you hook up two of them" that is what accounts for the difference.

absolutely incorrect
your perception or 'looking' has nothing to do with it
the math and physics do not lie

 

[Ingenieur]

Well, the original discussion is some people mistakenly call a single phase xfmr "two phase" when the winding is tapped in the center. I further asserted if it really was two phase, one could start an induction motor without the use of starting apparatus as a proof that people are mistaken if they think it is two phase. Those who mistakenly called it two phase were schooled in xfmr theory, and then they began offering other excuses as to why they call it two phase.

They failed to grasp the physics because they lack understanding of electrical xfmr theory.

It's one primary winding producing a single sine wave in the secondary, and this doesn't change just because it is center tapped

you are mistaken
there are 2 distinct and independant phases
you or no one else has proven otherwise, in fact it has been proven there IS

btw most on here know more than you ever will
it's not theory, it's ascertainsble fact, they KNOW how a xfmr functions
physically and mathematically
which you do not

 

[Ingenieur]

xfmr.

How about somebody just reading how a transformer works? Somebody provided a fairly accurate description of the coils and their additive property producing just one current, first in one direction, and then the opposite direction. Physics preclude the existence of opposing currents in a single phase xfmr

it has 3 windings
the fact that if balanced the neut is 0 PROVES opposite phases since both line i's are positive qtys (or of the same sign) at the node

 

[jaggedben]

Funny you should ask.

Like a voltage, it depends on your reference.

If I put N on the equator and L2 North, then the compass points North from L1-N and North from N-L2 (0 phase difference).

If I put N on the North Pole, then the compass points North from L1-N and North from L2-N (180 phase difference).

You pick the reference. Either way is valid. It really is that simple.

I'm really not catching your drift here. The two compass needles responding to the local magnetic field will both point the same direction.

 

[jumper]

Yes Jumper, 60-0-60 system. You can make one on the cheap with a 480/240 X 240/120 single phase transformer. I run both sides in series and use 240 on primary. It is alot like isolated power system used in hospitals.

Still looking for dialogue on what would be different with distorted waveform on true 180 vs -1.

I have worked with them in school and did a small set up for the physics guys to play with, but a 647 install is a bit tricky. Not worth the trouble for small scale operations.

As far as 180d or -1, either works here. I am not getting into distorted waveforms here. We gotta get the basics defined here before we move on IMO.

 

[jaggedben]

...

As far as 180d or -1, either works here. I am not getting into distorted waveforms here. We gotta get the basics defined here before we move on IMO.

I gotta chuckle at this...:happyno:

The whole question, IMO comes down to whether there is any practical utility in using one over the other. Since sin(x) = -sin(x+180), using one instead of the other to analyze the ideal voltage can be nothing more than which math operation one is more comfortable performing. It can't be more than a matter of preference. The real test is how the methods compare at cracking issues other than graphing the ideal voltages.

If you have an assymtrically distorted waveform, you really have a situation where if you can describe one waveform with f(x) then the other waveform needs to be described as -f(x).

If you have an inductive load on one leg and you want to calculate current on the neutral, you need phasor math.

There are no 'basics' that can be defined in a vacuum. You need some additional info about what real world aspect one is interested in looking at, to know if one is better off with one or the other.

 

[wwhitney]

there are 2 distinct and independant phases

No, the two phases are dependent, in that V_L1-N(t) + V_L2-N(t) = 0. That is the definition of dependent vectors.

Cheers, Wayne

 

[jumper]

Actually Ben, that is only one aspect of this thread IMO.

The physical construction, naming conventions, and differences at looking at the tranny secondary waveforms are others.

There is a displacement of 180d of the 2 120V signals WRT to da noodle. Why? Because it is what it is.

Gunny earlier posted this. As long as my arrows/vectors are correct I do not care how they got that way.

You'd just have two arrows sticking out in opposite directions, and you'd still have people arguing whether the second arrow got there by rotation about the center point or going back through the center to the other side.

 

[drktmplr12]

No, the two phases are dependent, in that V_L1-N(t) + V_L2-N(t) = 0. That is the definition of dependent vectors.

Cheers, Wayne

the degree to which L1-N is loaded does not impact the L2-N waveform in any way.

 

[Ingenieur]

No, the two phases are dependent, in that V_L1-N(t) + V_L2-N(t) = 0. That is the definition of dependent vectors.

Cheers, Wayne

nope
one line load R
one line load Z

does the pf of the R load change due to the Z line load?
no
independant

 

[jaggedben]

the degree to which L1-N is loaded does not impact the L2-N waveform in any way.

Does the load not effect the primary voltage in any way? How about the spin of a generator shaft?

 

[Ingenieur]

Does the load not effect the primary voltage in any way? How about the spin of a generator shaft?

same applies for 3 phase

 

[jaggedben]

same applies for 3 phase

Should I take that as an admission that a load on one phase does effect the waveform on the other phases, in some way?

What does this have to do with the previous discussion?

 

[Ingenieur]

Should I take that as an admission that a load on one phase does effect the waveform on the other phases, in some way?

What does this have to do with the previous discussion?

no
only that it is reflected in the primary

you brought it up!:lol:

 

[drktmplr12]

"Independent from each other" strikes me as a poor choice of words. I think your point is that they differ. But as long as they are derived from the same HV primary phase (or as gar pointed out, the same generator shaft), then they aren't entirely independent.

I also disagree with you about the L1 and L2 loads not being in series. It is only on the assumption that the resistance of the N conductor is negligible that you can ignore how they are in series. But I'm also not sure how that relates to the larger topic of this thread, which is about how we name waveforms.

We call the wave forms line 1 and line 2.

The impedance of the neutral, from the neutral bar to the service is negligible because in most cases the neutral current will be near zero.

The loads on each leg do not form a series circuit. That would imply the currents must travel back to the service point and then back through the neutral, through l2 loads, then through l2 line conductors to return to the source. Why would they do that when they can return to the source once they hit the neutral bar? Lower impedance path.

It's the same reason you shouldn't start 240V loads if you for some reason lost either leg. The current would backfeed the 120v l2 loads.

Further if there was a series circuit the current direction along the entire circuit would be the same they are not they are opposite

Sent from my Pixel 2 using Tapatalk

 

[mivey]

Well, the original discussion is some people mistakenly call a single phase xfmr "two phase" when the winding is tapped in the center. I further asserted if it really was two phase, one could start an induction motor without the use of starting apparatus as a proof that people are mistaken if they think it is two phase. Those who mistakenly called it two phase were schooled in xfmr theory, and then they began offering other excuses as to why they call it two phase.

They failed to grasp the physics because they lack understanding of electrical xfmr theory.

It's one primary winding producing a single sine wave in the secondary, and this doesn't change just because it is center tapped

Please stop doing that. Try to treat your fellow members here with respect. We are trying to have a civil discussion. We are not enemies here, we just don't see eye-to-eye on everything.

I honestly tend to ignore posts like that and I would think if you want people to read your thoughts then clean it up.

Quit talking about people and just focus on talking about what was said. Talk like that is inflammatory and can cause others to respond in kind which creates problems.

If it comes down to it, hopefully the mods would find it better to punish an individual for dragging down a thread rather than punish the group as a whole.

 

[mivey]

xfmr.

How about somebody just reading how a transformer works? Somebody provided a fairly accurate description of the coils and their additive property producing just one current, first in one direction, and then the opposite direction. Physics preclude the existence of opposing currents in a single phase xfmr

Most of us know. Some better than others.

The transformer halves do not have matching currents. The current in the L1-N winding can be different than the current in the L2-N winding. The currents will only be exactly the same when the neutral wire is unused.

The easiest example is a single load connected L1-N. One coil has full current and the other has zero.