120<0 + 120<0 = 240<0
or
120<0 - 120<180 = 240<0
or
120<180 - 120<0 = 240<180
There are several choices that can be made for analysis.
240v debate....
- Thread starter stickboy1375
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120<0 + 120<0 = 240<0
or
120<0 - 120<180 = 240<0
or
120<180 - 120<0 = 240<180
There are several choices that can be made for analysis.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
This is why I am starting with a two wire load from both a single source and two sources in series.
I have not made any statement at all about which voltage direction to choose.
And yes, employing math tricks does make solving some equations easier.
You continually say that the choice of a reference is arbitrary, but you also seem to refuse to use any reference other than a neutral (hence part of my insistence to stay away from wye connected 3-phase).
The choice of reference is arbitrary but the signs you apply during circuit analysis are not arbitrary. If you're solving with:
B-A = 240<0
then B-N = 120<0 and N-A = 120<0 which becomes 120<0 (B-N) + 120<0 (N-A) = 240<0 (B-A)
or N-A = 120<0 and N-B = -120<0 which becomes 120<0 (N-A) - -120<0 (N-B) = 240<0 (B-A)
jumper
Senior Member
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- 3 Hr 2 Min from Winged Horses
Er, why did you quote me in my response to John when you posted this?
I appreciate you adding to this thread, but I am not in contention with the analysis' being presented. I am only here to learn, not present a point of view on analysis.
jumper
Senior Member
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- 3 Hr 2 Min from Winged Horses
Read the second quote in that post.
I did. It baffles me. I never heard of the guy nor understand what he said.
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- Simi Valley, CA
mivey
Senior Member
ok
No, it does not mean that. That choice is arbitrary.
I do not swap directions. I choose the voltage rise to be away from the ground bus. Just like we can take voltages to be towards or away from a surface. At least with with a ground bus reference I do not have to move my reference point. With voltages Vna and Vbn, the reference for Vna is "a" and the reference for Vbn is "n".
No, they do not. The voltages force can be taken in either direction. The choice is arbitrary.
"Straight" does not mean the voltages were created in phase. See my generating example from post #98 where the generator shaft is rotated 180?. If you want to keep the voltages directions linked to the source, the "straight" comes from the fact that one force is "pushing" at the same time the other is "pulling". The end result is that is does not matter as we can take the voltages to be in either direction because a voltage is defined by its reference.
It is an actual force and the choice of direction is arbitrary.
No, it is not like that at all. Refer to my post #98 and you will see that the ends are not "going up and down together", but you can see that they still "see-saw".
mivey
Senior Member
But none of those choices means other voltages do not exist.
mivey
Senior Member
When you choose to (paraphrasing) "start with two sources in series", you have in fact made a choice about voltage directions.
Also, I do not "refuse" to use the other reference. I am saying that both are valid references. In fact, I will agree (and have said so many times in the past) that in most cases, in makes the analysis much easier to consider Vbn and Vna.
But easy or not, the voltage in the other direction is a real voltage. Just because we have become accustomed to using the easier analysis does not mean we get to ignore the way voltages are defined.
I understand that we can become accustomed to thinking about things in a certain way because it is easier to remember, fits nicely in a little box in our storage area, etc.. But if we want to get out of the little pigeon holes, we have to go back to the fundamentals and see what underlying simplifying assumptions may have been made before we stored our sterilized bit of information in our memory box.
jwelectric
Senior Member
- Location
- North Carolina
I was on top of an "A" frame ladder about 16 feet above the concrete floor when I fell.
Now that the actual force and my choice of direction was arbitrary I sure wish I had fell upwards as I was only a couple of feet from the ceiling.
Damn Newton and his apple
I don't believe my choice has much to do with what is happening
Rick Christopherson
Senior Member
You seem to have a propensity for missing the point or unnecessarily complicating it. You might do better to emulate William of Ockham.
Nobody is suggesting that anything extraordinary is going on with the flux. The simple fact (yes, fact) is that, for the single phase centre-tapped transformer, Van and Vbn are mutually displaced by 180deg.
mivey
Senior Member
But your loss was another's gain. The potential energy you lost was gained by the Earth when you interacted with it.
You would testify in court that you fell to Earth. Had you weighed more, a lot more, you would say the Earth ran into you. That is a direction choice.
The fact is that the distance between you and the Earth was reduced, probably rather quickly. Now, we have become accustomed to the direction convention that says you climbed up the ladder and then you fell down from the ladder. But if we go back to the fundamentals, we know that the gravitational force between two objects is G*m1*m2 / r^2.
There is no universally defined direction for r. But because the mass of the Earth is about 6x10^24 kg, we usually reference gravitational forces relative to the Earth's position. Gravitational fundamentals will tell you that both directions are valid and the choice of direction is arbitrary, even though your sore behind would argue that only one direction is valid.
It may be of little comfort, but had you fallen when the Moon was directly overhead, it would have lessened your impact ever so slightly.
jwelectric
Senior Member
- Location
- North Carolina
If at the last second before impact I had of jumped at a 180 degree angle from the ladder then all energy would have been released before I made contact with the concrete, :? do you agree?
mivey
Senior Member
Rick and Jim are looking at the green grass and the blue sky and have agreed that because of our eye positioning, you can only look in one direction or the other so you must choose to look down at the green grass or up at the blue sky. Now there is some question in their mind about which way to look first so they try to look around and find some reference to tell them if up or down is correct. I mean after all, we can only look in one direction at the time so one direction must be correct, right? They insist that if you look at the blue sky first then that disallows looking at the green grass first.
Besoeker & I hear this and tell them that, for one thing, either direction is ok because there is no universal law that states which way they must look first. We also point out that if they would just raise their heads to a neutral position, they could see both the green grass and the blue sky at the same time. Jim & Rick claim the neutral head position is just a math trick because you can't see both the sky and grass at the same time.
My pet chameleon appears puzzeled by all this "up" "down" & "neutral" talk as he points one eye at the sky and one eye at the grass and says: "So does this mean I'm going to get some lunch or what?"
Besoeker & I hear this and tell them that, for one thing, either direction is ok because there is no universal law that states which way they must look first. We also point out that if they would just raise their heads to a neutral position, they could see both the green grass and the blue sky at the same time. Jim & Rick claim the neutral head position is just a math trick because you can't see both the sky and grass at the same time.
My pet chameleon appears puzzeled by all this "up" "down" & "neutral" talk as he points one eye at the sky and one eye at the grass and says: "So does this mean I'm going to get some lunch or what?"
mivey
Senior Member
On the way to the ground, your potential energy was temporarily in the form of kinetic energy. Right before impact that was in the form of 1/2*m*v^2 (mass moving at a particular velocity). You would have to have some means to convert the kinetic energy into some form of energy that would not hurt you or at least change the speed of conversion and maybe burn off some of the energy in the process.
You could convert that to energy in a spring and use it to regain your potential energy (i.e. a trampoline). But if you were strong enough, you could land on your feet and burn some of that energy off in heat as you accelerate in the opposite direction using your muscles. The remaining energy conversion would then not hurt as bad as it would happen over a longer period of time. Power is a measure of how fast we exchange energy over time. When you hit the floor the first time, at lot of energy was exchanged in a short period of time, and that hurts. Slowing this exchange will not hurt as bad. It did not hurt when you walked up the ladder did it?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Are you saying that a center tapped transformer is not two sources in series?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
When have I said you must do something?
I have stated that the presence or absence of a load neutral should not require a change in the way the sources are viewed.
I have asked you to solve a simple loop that would be typical of a 120/240V center tapped transformer that looses the load neutral connection. I figured you would get the same load voltage and current relationships as Besoeker would, solving the loop using his equivalent residential supply of 240V.
Oh yeah, I have suggested that it should be explicitly mentioned that the neutral point is your reference when you say 120<0 and 120<180 combine to be a 120/240V source.
No, the potential was converted to kinetic and then to deformation. The potential is gone.
Since due to inertia and friction the Earth did not move at all, his testimony is correct. To move the Earth he wouldn't be he.
Yes there is a defined direction for r. It's an absolute distance and therefore never negative.
Which would have required keeping the mathematical vector signs correct.It may be of little comfort, but had you fallen when the Moon was directly overhead, it would have lessened your impact ever so slightly.
Show the simple math on the 240V system Mivey. You can't solve the equations without using double negatives for your choice of reference.
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