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

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jumper

jumper

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jaggedben said:
Okay, let's get back on track... :D



Do 'phase' and 'in-phase' and 'out of phase' have a sufficiently defined, agreed upon, industry standard meaning that could be deployed to characterize the 120/240 volt system? Or are they just another example of vague or misused terminology?

I submit that I'm unaware of any such definition.

Specifically, I'm unaware of such a definition that precludes two waveforms with the same zero-crossings from being 'in-phase.' Not saying (yet?) that it should or shouldn't preclude such, just that I haven't seen the definition.
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Gimme a sec. Gotta reply correctly.
 
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Ingenieur

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[FONT=&quot]Phase can also be an expression of [/FONT]relative displacement[FONT=&quot] between two corresponding features (for example, peaks or zero crossings) of two waveforms having the same [/FONT]frequency[FONT=&quot].[/FONT][1]

The amount by which such oscillators are out of phase with each other can be expressed in degrees from 0° to 360°, or in radians from 0 to 2π. If the phase difference is 180 degrees (π radians), then the two oscillators are said to be in antiphase. If two interacting waves meet at a point where they are in antiphase, then destructive interference will occur. It is common for waves of electromagnetic (light, RF), acoustic (sound) or other energy to become superposed in their transmission medium. When that happens, the phase difference determines whether they reinforce or weaken each other. Complete cancellation is possible for waves with equal amplitudes.
 
jumper

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ggunn said:
There's a track? :D
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Of course, this guy apparently did not understand that.:D

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GoldDigger

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jaggedben said:
Okay, let's get back on track... :D



Do 'phase' and 'in-phase' and 'out of phase' have a sufficiently defined, agreed upon, industry standard meaning that could be deployed to characterize the 120/240 volt system? Or are they just another example of vague or misused terminology?

I submit that I'm unaware of any such definition.

Specifically, I'm unaware of such a definition that precludes two waveforms with the same zero-crossings from being 'in-phase.' Not saying (yet?) that it should or shouldn't preclude such, just that I haven't seen the definition.
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Although possibly not rigorously defined, two waveforms with different shapes ate often described as "in phase" if their zero crossings coincide (possibly only if their slopes match at the zero crossings too.
On example would be a simple sine wave and its third harmonic.
Two cosine waves (fundamental and harmonic) with no additive factor in the time term could also be described as in phase, although it would be the maxima that line up at t=0.

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gar

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180805-0727 EDT

Given any arbitrary periodic waveform of fundamental frequency f all harmonics in that waveform have a fix phase relationship to that fundamental.

Note: a periodic waveform has a repetitive structure that extends from - to + infinity. Any one cycle is indistinguishable from any other cycle. Any interruption of this periodicity makes the signal non-periodic, and therefore a transient.

.
 
Besoeker

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jumper said:
If I am talking to you, we can call it two phases and discuss it from that point of view.

But if I am referring to it per common usage and NEC terms, it’s single phase.
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Yes I know. Excuse my frivolity.

We commonly use terms that are not entirely logical. 120Vac for example.
 
jumper

jumper

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Besoeker said:
Yes I know. Excuse my frivolity.

We commonly use terms that are not entirely logical. 120Vac for example.
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Actually, it is not frivolous. It is one of my key points in this thread.

I know exactly what you are talking about, but as others have said-we have so many different levels of education, experience, and training that these discussions go haywire.

How you and I are going to talk is gonna be way different than the way I talk to apprentices and jws. They need the basics to get licensed.

If they continue to go forward, then I get into more advanced stuff.
 
Besoeker

Besoeker

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jumper said:
Actually, it is not frivolous. It is one of my key points in this thread.

I know exactly what you are talking about, but as others have said-we have so many different levels of education, experience, and training that these discussions go haywire.

How you and I are going to talk is gonna be way different than the way I talk to apprentices and jws. They need the basics to get licensed.

If they continue to go forward, then I get into more advanced stuff.
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I quite agree. I have given quite a few training courses over the years. Mostly it was for maintenance electricians in plants that had our kit. The spectrum of knowledge made it difficult to tailor the content of the courses to suit all. For some it was clearly just an opportunity to skive off work.

A little background if I may. Mods be patient.
I've been retired a few years now. The division of Eaton that I ran was a specialised niche. Not long after I left, the guy who was my chief engineer also departed. That left a vacuum in the knowledge of systems we supplied. Customers voted with their feet and another company got the support business.Earlier this year, I was invited to give them a training course. These were qualified guys with knowledge and experience in the drives field. It was much more rewarding teaching them.
 
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jaggedben

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GoldDigger said:
Although possibly not rigorously defined, two waveforms with different shapes ate often described as "in phase" if their zero crossings coincide (possibly only if their slopes match at the zero crossings too.
Click to expand...

That last bit isn't incidental to this thread. If it is just zero crossings that matter, then all three voltage waveforms on the 120/240 system are 'in-phase'.


One example would be a simple sine wave and its third harmonic.
Click to expand...

Wouldn't it be any harmonic, by definition?

Two cosine waves (fundamental and harmonic) with no additive factor in the time term could also be described as in phase, although it would be the maxima that line up at t=0.
Click to expand...

So if a harmonic that coincides at the zero crossings and maxima is 'in phase', how could a waveform 180deg apart (or inverted) not be in phase?
 
jumper

jumper

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Okay, I am gonna need more coffee if we are go there Ben. I will jump in later on this.

But back to one aspect, we, the electrical community, definitely have problems with defining systems and the terminology used in basic tranny methodology. Too many only know only one aspect or another. Both are valid.

At some point an experienced person should know what the other person is saying by their context and reasoning.

I mean, I see your point and you see mine. We differ, but not argue.
 
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