Where do we use the 1.73 when calculating 3 phase
- Thread starter ronaldrc
- Start date
- Status
Re: Where do we use the 1.73 when calculating 3 phase
I am quite sure that there are MANY more lurking and reading and learning from these threads than we might suspect. As a part time instructor, I am very heartened to find this kind of discussion taking place. Sometimes I think that teaching apprentices is like hearding cats. If they don't want it, they won't pick it up, but, it is up to us to make them want it.
Well now that was quite a rant. I do truly enjoy the discussions. Thank You all. Garrett
I am quite sure that there are MANY more lurking and reading and learning from these threads than we might suspect. As a part time instructor, I am very heartened to find this kind of discussion taking place. Sometimes I think that teaching apprentices is like hearding cats. If they don't want it, they won't pick it up, but, it is up to us to make them want it.
Well now that was quite a rant. I do truly enjoy the discussions. Thank You all. Garrett
Re: Where do we use the 1.73 when calculating 3 phase
Thought I would rattle off again.
Ed and Rattus I was taught and thought I learned Threepase 30 some odd years ago.
Rattus I understand you have a very good working knowledge of the field although you
seem to have specialize in electronics that is a plus.
I still believe its like Ed said and I have said all alone, throwing complex math terms
out in the blue is not going to help anybody.
First you need to understand the basic mechanics of how a alternator works.
Then you have to know that a Threepase alternator is really 3 generators in one.
And just telling someone without that basic knowledge that B phase is 120 electrical
degrees behind A phase want work.
After they understand the mechanics envolved with the alternator. The main emphasis
needs to be put on the timing. They need to be aware that just only one phase has a peak
RMS at any one time. If the positive pole or north pole of the alternator field is pointing
dead center with the A phase armature A phase is at its peak RMS or its highest voltage.
The north pole of the armature will not be inducing a voltage into phase B until the
armature has turned a 1/4 of another turn which is another 30 degrees later. First 1/4 of
the cycle A phase is peaked out and before A phase has gone all the way to zero 30
degrees later the north pole field starts inducing a voltage into B phase. Then the same
thing on to C phase.
First glance at a 3 phase delta diagram you first hunch is that one heater is on A phase
and another heater is on B phase and we are using the one conductor to feed both so logic
without a lot of thought tells you the heaters are in parallel so they will pull twice the
current of one heater. But do not forget that when the A phase generating a voltage for
the heater on the A phase that is from line #1 to line #2 that there is no voltage being
generated into B phase which is from line #2 to line #3.
This is really not that complicated, but you do have to apply your mind and once you
grasp this you will figure where the constant multiplier or 1.73 comes in.And you do
have to be using the third leg or all three phases before we use it.
Ronald
Thought I would rattle off again.
Ed and Rattus I was taught and thought I learned Threepase 30 some odd years ago.
Rattus I understand you have a very good working knowledge of the field although you
seem to have specialize in electronics that is a plus.
I still believe its like Ed said and I have said all alone, throwing complex math terms
out in the blue is not going to help anybody.
First you need to understand the basic mechanics of how a alternator works.
Then you have to know that a Threepase alternator is really 3 generators in one.
And just telling someone without that basic knowledge that B phase is 120 electrical
degrees behind A phase want work.
After they understand the mechanics envolved with the alternator. The main emphasis
needs to be put on the timing. They need to be aware that just only one phase has a peak
RMS at any one time. If the positive pole or north pole of the alternator field is pointing
dead center with the A phase armature A phase is at its peak RMS or its highest voltage.
The north pole of the armature will not be inducing a voltage into phase B until the
armature has turned a 1/4 of another turn which is another 30 degrees later. First 1/4 of
the cycle A phase is peaked out and before A phase has gone all the way to zero 30
degrees later the north pole field starts inducing a voltage into B phase. Then the same
thing on to C phase.
First glance at a 3 phase delta diagram you first hunch is that one heater is on A phase
and another heater is on B phase and we are using the one conductor to feed both so logic
without a lot of thought tells you the heaters are in parallel so they will pull twice the
current of one heater. But do not forget that when the A phase generating a voltage for
the heater on the A phase that is from line #1 to line #2 that there is no voltage being
generated into B phase which is from line #2 to line #3.
This is really not that complicated, but you do have to apply your mind and once you
grasp this you will figure where the constant multiplier or 1.73 comes in.And you do
have to be using the third leg or all three phases before we use it.
Ronald
Re: Where do we use the 1.73 when calculating 3 phase
ronald,
You are right about the math, most will not understand it, but for the few who do, it should help clear things up. And I see no other way to adequately explain the 1.732 factor. Ed's diagram provides a graphical interpretation, but without a little trig, how do you quantify the unknown side? I just wish Ed would put arrowheads on his vectors!
I suspect also that there are some who took some trig back in the dark ages and may be prompted to bone up just enough to understand vectors.
On 3-phase generation, I think it is sufficient to say that the three phases are generated 120 degrees apart. In time that is 5.56 milliseconds apart. No need to go into the details of the alternator though.
I would say also that the magic number must be applied to any two legs of a wye to determine the line voltage. Three legs are not required.
[ February 20, 2005, 05:54 PM: Message edited by: rattus ]
ronald,
You are right about the math, most will not understand it, but for the few who do, it should help clear things up. And I see no other way to adequately explain the 1.732 factor. Ed's diagram provides a graphical interpretation, but without a little trig, how do you quantify the unknown side? I just wish Ed would put arrowheads on his vectors!
I suspect also that there are some who took some trig back in the dark ages and may be prompted to bone up just enough to understand vectors.
On 3-phase generation, I think it is sufficient to say that the three phases are generated 120 degrees apart. In time that is 5.56 milliseconds apart. No need to go into the details of the alternator though.
I would say also that the magic number must be applied to any two legs of a wye to determine the line voltage. Three legs are not required.
[ February 20, 2005, 05:54 PM: Message edited by: rattus ]
Re: Where do we use the 1.73 when calculating 3 phase
Rattus
I understand what you are saying about the magic number for wye.
But if we are talking about 208 the magic number has already been applied to bring it down to the effective voltage of 208 and we don't use it again if where working with single phase. Is that not right?
edited to add this: I see where we are differing here I am strictly talking about single phase and you are talking about getting the effect voltage of the Wye configure.
[ February 20, 2005, 06:32 PM: Message edited by: ronaldrc ]
Rattus
I understand what you are saying about the magic number for wye.
But if we are talking about 208 the magic number has already been applied to bring it down to the effective voltage of 208 and we don't use it again if where working with single phase. Is that not right?
edited to add this: I see where we are differing here I am strictly talking about single phase and you are talking about getting the effect voltage of the Wye configure.
[ February 20, 2005, 06:32 PM: Message edited by: ronaldrc ]
Re: Where do we use the 1.73 when calculating 3 phase
Ronald,
All the voltages are effective (RMS) voltages. Electricians seldom if ever deal with peak or average voltages. I am pointing out that the magic number must be applied to convert the phase voltage, 120, to the line voltage, 208, even if only two legs are involved. This may have been done already, but someone had to do it.
If a load is then connected across the 208V, we have a single phase problem as you say.
Ronald,
All the voltages are effective (RMS) voltages. Electricians seldom if ever deal with peak or average voltages. I am pointing out that the magic number must be applied to convert the phase voltage, 120, to the line voltage, 208, even if only two legs are involved. This may have been done already, but someone had to do it.
If a load is then connected across the 208V, we have a single phase problem as you say.
crossman
Senior Member
- Location
- Southeast Texas
Re: Where do we use the 1.73 when calculating 3 phase
Rattus:
Keep posting the math! I like to ponder it, of course I also like to hear the "for the layman" explanations and diagrams that Ed adds to the threads.
The math you posted in a couple of other threads that I was involved in did indeed cause me to go to "Half-Price Books" and pick up a couple of college Physics texts and a college Calculus text, and I have been spending a good deal of time in them. I cetainly thank you for that!
I took Physics and Calculus over 20 years ago, but I was just a kid and did not learn it like I should have. I consider myself to be quite decent at teaching basic AC theory involving the RMS values, vectors, PF, etc. The trig of solving the vectors is straightforward and easy to teach. I also try to teach more than just the math, I try to teach the concepts of capacitance, inductance, etc.
Still, there is a whole lot more out there that I do not understand. Yet as I grow older, possession of that knowledge seems more and more important to me. Sure, I may never actually use the knowledge in the field, but that makes no difference. Having the knowledge is the reward in and of itself.
On that note, I want to personally thank Rattus, Ed, Charlie, iwire, Steve66, and everyone else who freely gives of their knowledge on this site. Posting this stuff does take time out of your busy lives, yet you give your knowledge for the rest of us. Again, THANKS!
One last note: When I was standing at the counter to pay for the 2 physics texts and the calculus text, the salesperson says "That will be 19 dollars and 27 cents." A shiver went through me... I said to her "Do you realize how much knowledge I just bought for a mere $20?"
Gas to the bookstore = $1.68
Paper and ink in the books = $19.27
Knowledge contained there-in = PRICELESS
Keep the good stuff coming guys!
Rattus:
Keep posting the math! I like to ponder it, of course I also like to hear the "for the layman" explanations and diagrams that Ed adds to the threads.
The math you posted in a couple of other threads that I was involved in did indeed cause me to go to "Half-Price Books" and pick up a couple of college Physics texts and a college Calculus text, and I have been spending a good deal of time in them. I cetainly thank you for that!
I took Physics and Calculus over 20 years ago, but I was just a kid and did not learn it like I should have. I consider myself to be quite decent at teaching basic AC theory involving the RMS values, vectors, PF, etc. The trig of solving the vectors is straightforward and easy to teach. I also try to teach more than just the math, I try to teach the concepts of capacitance, inductance, etc.
Still, there is a whole lot more out there that I do not understand. Yet as I grow older, possession of that knowledge seems more and more important to me. Sure, I may never actually use the knowledge in the field, but that makes no difference. Having the knowledge is the reward in and of itself.
On that note, I want to personally thank Rattus, Ed, Charlie, iwire, Steve66, and everyone else who freely gives of their knowledge on this site. Posting this stuff does take time out of your busy lives, yet you give your knowledge for the rest of us. Again, THANKS!
One last note: When I was standing at the counter to pay for the 2 physics texts and the calculus text, the salesperson says "That will be 19 dollars and 27 cents." A shiver went through me... I said to her "Do you realize how much knowledge I just bought for a mere $20?"
Gas to the bookstore = $1.68
Paper and ink in the books = $19.27
Knowledge contained there-in = PRICELESS
Keep the good stuff coming guys!
Ed MacLaren
Senior Member
Re: Where do we use the 1.73 when calculating 3 phase
I would, if it was presented as a vector diagram. (referring to my diagram above on Feb 19)
It is just what it's caption states - "A mechanical analogy of vectorial addition."
I wish there was an "electrical machine winding" person active on the forum, who would review those basic alternator sketches that we discussed.
Ed
Hi Rattus,
I would, if it was presented as a vector diagram. (referring to my diagram above on Feb 19)
It is just what it's caption states - "A mechanical analogy of vectorial addition."
I haven't given up on this one yet.
I wish there was an "electrical machine winding" person active on the forum, who would review those basic alternator sketches that we discussed.
Ed
Re: Where do we use the 1.73 when calculating 3 phase
Ed, seems to me that it is sufficient to imagine three single phase alternators on a single shaft with the shafts skewed to provide the 120 degree separation. I think going into the details of 3-phase generation should be a separate topic for the student.
Ed, seems to me that it is sufficient to imagine three single phase alternators on a single shaft with the shafts skewed to provide the 120 degree separation. I think going into the details of 3-phase generation should be a separate topic for the student.
Re: Where do we use the 1.73 when calculating 3 phase
Ed, seems to me that it is sufficient to imagine three single phase alternators on a single shaft with the shafts skewed to provide the 120 degree separation. I think going into the details of 3-phase generation should be a separate topic for the student.
Ed, seems to me that it is sufficient to imagine three single phase alternators on a single shaft with the shafts skewed to provide the 120 degree separation. I think going into the details of 3-phase generation should be a separate topic for the student.
- Status