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

[GoldDigger]

Whatever Steinmetz may have said about (in effect) 120-0-120 being a special case of two independent phases, the fact remains that that special case produces a one dimensional phasor space unless reactive elements are used to produce a phase shift. And those reactive elements introduce different phase shifts for each harmonic, potentially distorting the original waveform (unless you have only the fundamental present.)

Sent from my XT1585 using Tapatalk

 

[LarryFine]

What amuses me is that electricians understand this simplicity, but those claiming to be engineers do not. It tells me they don't even know what they looking at with a scope:jawdrop:

Thank you. I've been told that I understand theory better than the average electrician.

Engineers have been known to over-think things.

Although Mivey seems to disagree with some of my assertions, I stand by them.

 

[jumper]

current is not a magnetic field
current is the resultant work performed due to emf

:happysad:

Current is a rate of flow.

“A current of 1 ampere means that there is 1 coulomb of charge passing through a cross section of a wire every 1 second.

1 ampere = 1 coulomb / 1 second”

http://www.physicsclassroom.com/class/circuits/Lesson-2/Electric-Current

 

[jumper]

Thank you. I've been told that I understand theory better than the average electrician.

You do IMO

Engineers have been known to over-think things.

They are engineers. That’s their job.

Although Mivey seems to disagree with some of my assertions, I stand by them.

There are some minor flaws that he pointed out, I understand why, but I see the analogies useful for answering the OP s question and others trying to figure this out.

.

This topic gets blown out every time. Watch the spiraling out of control begin.

 

[Russs57]

Okay, given I started this up again, let me ask for a recap. This is what I think has been said.

We do not have two phases 180 degrees apart in time. We have one phase, that when viewed from the center tap, has one windings polarity inverted (multiply by -1). This is indistinguishable from a 180 phase shift in time, as long as we are looking at a pure sine wave. Once we have loads that cause distortions/harmonics then the difference, between inverted polarity and 180 degree phase shift, becomes apparent.

Close enough?

 

[mbrooke]

Thank you. I've been told that I understand theory better than the average electrician.

Engineers have been known to over-think things.

Although Mivey seems to disagree with some of my assertions, I stand by them.

Larry, you understand theory, code, business, computer, time travel, and a whole host of other things better than an average electrician. I especially admire your simple yet still technically correct explanation to complex problems.

 

[LarryFine]

Flattery'll get you everywhere.

 

[buffalonymann]

:happysad:

Current is a rate of flow.

“A current of 1 ampere means that there is 1 coulomb of charge passing through a cross section of a wire every 1 second.

1 ampere = 1 coulomb / 1 second”

http://www.physicsclassroom.com/class/circuits/Lesson-2/Electric-Current

Yeah, and it's flowing because work is being done

 

[LarryFine]

Yeah, and it's flowing because work is being done

One could say that work is being done because current is flowing.

 

[mivey]

Bbow up your scope leads.

Well, yeah, there is that minor inconvenience.

 

[mivey]

Correct- for polarity, but power says otherwise. In in a system with a 5 degree phase difference one phase will give power when the other one does not.

Re-phrase that please so I can see what you meant.

 

[buffalonymann]

There are three terminals and two equal magnitude waveforms. We can all agree L1-N and L2-N have waveforms with a 180 degrees difference. Reverse the terminals on the 2nd measurement and you have changed the polarity so there are now two waveforms with a zero degree difference.

Ok - why do you continue to say there are two wave forms?

When the primary completes one cycle, the secondary completes one cycle - nothing more. From l1 to l2 there is only one wave form, another wave is not create because we tap into coil midway. the only way to get additional wave is to have additional primary out of phase with first primary

 

[mivey]

current is not a magnetic field
current is the resultant work performed due to emf

Current is charge flow. A moving charge creates a magnetic field. Separation of charges create an electric field.

Thus, electric fields are associated with voltage and magnetic fields are associated with current.

 

[mivey]

Flattery'll get you everywhere.

Just don't make any sudden stops!

 

[zbang]

Yeah, and it's flowing because work is being done

Regardless of your assertions, the International System of Units (SI) tells us that volt is the unit of electrical potential (pressure), that ampere is the unit of electrical current (flow), and that watt is the unit of power (work performed). (Exact definitions and derivations are available from the link above.)

Agree or not, that's how the vast majority of electricians/engineers/physicists/etc use the words & concepts.

 

[LarryFine]

Agree or not, that's how the vast majority of electricians/engineers/physicists/etc use the words & concepts.

Why can't the same logic be applied to the topic of discussion? :roll:

 

[zbang]

Why can't the same logic be applied to the topic of discussion? :roll:

Because then we wouldn't have run on for almost 200 messages.

 

[wwhitney]

Okay, given I started this up again, let me ask for a recap. This is what I think has been said.

We do not have two phases 180 degrees apart in time. We have one phase, that when viewed from the center tap, has one windings polarity inverted (multiply by -1). This is indistinguishable from a 180 phase shift in time, as long as we are looking at a pure sine wave. Once we have loads that cause distortions/harmonics then the difference, between inverted polarity and 180 degree phase shift, becomes apparent.

Close enough?

Sounds good to me.

Cheers, Wayne

 

[mbrooke]

Re-phrase that please so I can see what you meant.

A 180* phase shift system either provides power or does not, meaning when any one phase hits zero volt/amps, the other phase hits zero volt/amps where as in a 3 phase system when any one phase hits zero volt/amps the other two are still supplying power at various degrees.

I know that this is elementary, but my point being that when the blue phase is at the zero crossing and is essential "dead" (no voltage or current) the red phase is heading toward its peak voltage, while the green phase is dropping from is peak. Any thing connected across red and green (like a motor winding) has current going through it and as such doing work. Same goes for a 2 phase system, when phase A is at peak, phase B is at zero of visa-veras

 

[mivey]

A 180* phase shift system either provides power or does not, meaning when any one phase hits zero volt/amps, the other phase hits zero volt/amps where as in a 3 phase system when any one phase hits zero volt/amps the other two are still supplying power at various degrees.


I know that this is elementary, but my point being that when the blue phase is at the zero crossing and is essential "dead" (no voltage or current) the red phase is heading toward its peak voltage, while the green phase is dropping from is peak. Any thing connected across red and green (like a motor winding) has current going through it and as such doing work. Same goes for a 2 phase system, when phase A is at peak, phase B is at zero of visa-veras

The distinction is clearer when you use two waveforms to run one circuit. Like when we only use the positive halves of the two waves like we do with a 2-diode full-wave rectifier. This is a circuit that makes use of the 180d difference.

Most other circuits do not utilize more than one waveform from the selection available.

When you only use one waveform, it is hard to appreciate the fact that the transformer can supply two waveforms with a 180d displacement. You could build these 180d displacements using a gen-set but why do that when the transformer can substitute?

Anyway, if you focus on the positive halves of the waveforms, you can see the work is done with a 180d displacement. An example would be the charging of a VFD using the positive pulses produced 180d apart.

Again, we could provide these 180d positive pulses from a set of two 180d displaced voltages using a common generator shaft with 180d displaced windings but one should be able to recognize that the center-tapped transformer can also supply this set of voltages.

Until you can step back and recognize that multiple sets can ultimately map to the same physical space, it is hard to see that they lay on top of each other but still exist.

As an example of looking beyond what may appear on the surface, you may or may not be aware of n-th roots. Just because you found one solution to an equation does not mean you found them all.