ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Electrical Engineer - Photovoltaic Systems
Relative to what? Without a reference point, a wave does not have a phase angle.
Whadda ya think?
- Thread starter rattus
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Relative to what? Without a reference point, a wave does not have a phase angle.
mivey
Senior Member
Not any more. They put up a sign in the waiting area that reads: "No engineers allowed beyond this point"Do you tell that to the tech that does your wheel alignment?
Take your pick; it is arbitrary. But, we usually choose to measure from the positive going zero crossing to the origin of the plot.
Or, you can simply look at the expression for the sine wave, e.g.,
Vbn = 120Vrms(sin(wt) + PI)) PI is the phase angle.
OK then, Mr. Smartypants, riddle me this: When you look at yourself in the mirror you see your left and right sides swap places, so why doesn't it make you look like you are standing on your head?
I know, but I'll wait on dan to answer.
- Location
- Wisconsin
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- PE (Retired) - Power Systems
Who is the we you are referring to?
If the Vbn, in your example, was the output of a transformer, I would 'arbitrarily' choose the physical relationship between the primary and secondary voltages as my reference. This way I would make sure I was consistent for both single phase and poly-phase systems. For example, a single winding primary with a single winding secondary phi = 0, and PI would simply indicate an inversion not an opposition.
If the Vbn, in your example, is not the output of a single phase transformer, it involves an area of discussion in which I have choose not to enter in regards to this thread.
Most of the engineering community chooses the negative to positive transition as the reference point for a sine wave, but for cosines I would choose a peak--since it is arbitrary anyway.
I don't understand your choice of reference. A reference is a node, say the neutral. In bes's case, he chooses the neutral because Vbn is the voltage he needs to explain the workings of the rectifier circuit. It is awkward to write [-Vnb] instead of Vbn. Vbn is of course the inverse of Van and it is also phase shifted by PI radians. Even rbalex admits that a sine and its inverse cannot be in phase.
There is no way that inverses can be in phase.
An inversion is considered to be a phase shift of PI. You can't tell the difference. The inversion also creates an opposite phase.
Once we know the details about Van and Vbn, we can replace them with equivalent sources and not worry about the transformer any more.
But, that doesn't answer the question: Do you think the criteria for 'in phase' and 'of the same phase' are the same??
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- Massachusetts
Just a heads up, stay on topic, leave the jabs, insults and low key digs out of your posts.
As far as the other thread it is just to much work to edit out the BS so that one is gone.
As far as the other thread it is just to much work to edit out the BS so that one is gone.
T
T.M.Haja Sahib
Guest
Generally no.'in phase' is usually applied for relating two different phasors,for example voltage and current,whereas 'of the same phase' relates to the same phasor.
I don't think the units are part of the criteria for 'in phase' or 'of the same phase'.
By saying the 'same phasor', are you meaning a single phasor? Or, you do you mean they carry the same units, say voltage or current?
T
T.M.Haja Sahib
Guest
Are you trying to develop criteria outside the purview of measurement?
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Electrical Engineer - Photovoltaic Systems
So, should one call a high leg delta system "four phase power"? :blink:
mivey
Senior Member
since you don't have four equal magnitude voltages with phase displacements:no. But the high leg is a different single phase. What you have is multiple systems, of course.
The criteria are established by others, not I.
Now do you wish to answer my question?
T
T.M.Haja Sahib
Guest
A single phasor.It can have only one unit.
Say take voltage Vab.Its parts Van and Vnb,where 'n' is an arbitrary point between 'a' and 'b' on the phasor Vab, are of the same phase.
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But that is not the question which is:
Are the criteria for 'in phase' and 'of the same phase' the same?
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Electrical Engineer - Photovoltaic Systems
Some would say yes and some would say no. The ambiguity of language is inescapable. What is the meaning of "is"? You cannot nail that Jello to the wall no matter how many nails you use or how hard you pound them in. 2500+ posts have shown that pretty clearly.
jaggedben
Senior Member
- Location
- Northern California
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- Solar and Energy Storage Installer
Folks, we've really ought to acknowledge that there's a usage of 'phase' in the electrical industry that just doesn't appear in most dictionaries. We use 'phase' to refer to a combination of two ungrounded conductors in a multi-phase generation and distribution system. Some people may use it in other ways (hot to neutral?) but I think almost all of us will agree that we use it in this way, and that such use is intelligible to other electricians and engineers.
No matter how hard you try, this is not equatable to mathematical definitions of phase (e.g. angular quantity). And no matter how hard you try, there's no way you are going to get electricians or even engineers to stop using this electrical meaning of 'phase'. (Hopefully we can discourage people from calling one wire a phase, as some do, and encourage them to call it a leg. But that's another question.)
So as for rattus' question, my answer is no.
'In phase' means synchronized. We don't use the preposition 'in' to mean something else.
'Of the same phase' can refer to a mathematical phase or an electrical phase. One can create about as many electrical waveforms as one pleases from a single electrical phase (two conductors). Those waveforms may or may not be of the same mathematical phase, but they can be considered all 'of the same' electrical phase that powers them. So you'd better just say which you're referring to -mathematical or electrical phase - if you're not sure how your interlocutor is going to interpret it. Especially if you're making a technically important distinction ... which, thankfully, you probably won't be making much in real life. :roll:
No matter how hard you try, this is not equatable to mathematical definitions of phase (e.g. angular quantity). And no matter how hard you try, there's no way you are going to get electricians or even engineers to stop using this electrical meaning of 'phase'. (Hopefully we can discourage people from calling one wire a phase, as some do, and encourage them to call it a leg. But that's another question.)
So as for rattus' question, my answer is no.
'In phase' means synchronized. We don't use the preposition 'in' to mean something else.
'Of the same phase' can refer to a mathematical phase or an electrical phase. One can create about as many electrical waveforms as one pleases from a single electrical phase (two conductors). Those waveforms may or may not be of the same mathematical phase, but they can be considered all 'of the same' electrical phase that powers them. So you'd better just say which you're referring to -mathematical or electrical phase - if you're not sure how your interlocutor is going to interpret it. Especially if you're making a technically important distinction ... which, thankfully, you probably won't be making much in real life. :roll:
Not so fast. I have posted on another thread a reference which says in so many words that for waves to be 'in phase' their positive peaks must coincide. From that we can deduce that their valleys must also coincide as well as their similar zero crossings. That is more than just synchronized.
Of course they must also be of the same frequency and the waves must be sinusoids.
T
T.M.Haja Sahib
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jaggedben
Senior Member
- Location
- Northern California
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- Solar and Energy Storage Installer
Regardless of how one mathematically defines 'in phase', I still think 'of the same phase' has different criteria. Even with 'in phase', I think it may behoove one to acknowledge that there are technical jargon meanings of words, and there are common knowledge or dictionary meanings of words.
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