jumper
Senior Member
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Sorta, but don't these simple explanations only really work for resistive loads? Don't leading and lagging currents effect the results?
Neutral currents in depth
- Thread starter jumper
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Sorta, but don't these simple explanations only really work for resistive loads? Don't leading and lagging currents effect the results?
jumper
Senior Member
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- 3 Hr 2 Min from Winged Horses
Thanks. I will go and look it up.
Probably start here.
http://www.allaboutcircuits.com/vol_2/chpt_11/3.html
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- Wisconsin
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- PE (Retired) - Power Systems
And it helps if your model ignores the real world relationship between current flow, winding directions, and magnetic flux.
But, that is the nice thing about mathematical models, you can use them to prove your point.
And yes the currents in the neutral of a single winding center-tapped transformer are 180? out of phase in the neutral even though they are in phase with each other in the transformer winding. According to the IEEE and ANSI standards for transformer labeling transformers, the top half current is flowing out of X1 towards neutral and the bottom half current is flowing out of neutral towards X2 (of course this top-bottom pattern alternates with the frequency).
kwired
Electron manager
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- NE Nebraska
The simple descriptions are still good enough for most applications. I don't think pure inductive or reactive loads change anything, as net impedance will still follow the rules of the simple explanations. Start throwing non linear loads in the mix and it can get complicated pretty fast.
But I'm not an engineer and have been told by one I have no business understanding electrical theory:jawdrop:
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- Wisconsin
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- PE (Retired) - Power Systems
X3 and X4 do not exist on a single winding center tapped transformer, they do however exist on a single core multi-winding unit. Again following the standard IEEE/ANSI convention X3-X4 have the same relationship as do X1-X2, otherwise we would not be able to parallel these windings in the X1X3-X2X4 120V arrangement shown on traditional transformer nameplates.
I find this resource from Cooper to be very helpful, even though it is written from a utility view point and it is relatively dated when it speaks of 'trends in the industry' (the original version is from pre-1988).
http://www.cooperindustries.com/con...urces/library/201_1phTransformers/R201902.PDF
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Attention!
This thread is a continuation of a discussion here, neutral current
I have moved it into it's own thread for clarity.
That is all well and good Jim, but with X2 tied to X3 wouldn't the voltage on X4 have to be 180 degrees out of phase from the voltage on X1 for the currents to behave in this way?
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- Wisconsin
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- PE (Retired) - Power Systems
The real world current relationships are fixed by the construction of the single core transformer winding(s).
The fact that you can mathematically model the voltages and currents as "180 degrees out of phase" does not mean they actually are.
I have stated in previous threads, it is my choice to consider a 3-wire 120/240V system as (2) 120V sources connected in in-phase and in series as it reduces the problems of currents and voltages being out of phase when a neutral conductor is either included or removed from a circuit.
No math tricks, Jim, Vx4n IS 180 degrees out from Vx1n. Besoeker has demonstrated this in the previous thread. Now VnX4 is in phase with Vx1n, but I am asking about Vx4n.
Of course you can do it any way you wish, and that is fine. I suspect that you agree with me and just won't admit it.
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- PE (Retired) - Power Systems
First this topic is about current.
Can you show me the physical connections that would allow the current in the top 1/2 of a transformer winding to be out of phase with the current in the bottom 1/2?
What is the relationship of the two winding currents that allow both a parallel connection at xV or a series connection at 2xV?
But since you brought it up: can you show me where I, or others, said that Vxy<>-Vyx or Vxy@0?<>Vyx@180??
I take great affront that you think my math skills are that poor.
what will it take to get you guys to finally stop trying to prove that 1-(-1)=2?
My point is: real world physics do not change simply because one reference point is chosen over another.
Where you have current you must have voltage.
The currents can be assumed to be in either direction. If the sense of one is wrong, the value will come out negative. You must specify the voltages correctly however.
It is fundamental that reversing the leads reverses the polarity of a dc measurement and reverses the phase angle of an AC measurement. I th
No offense intended.
Now if VL1 is at 0 degrees with current flowing outward, then what is the phase of voltage VL2 with current flowing inward. Both voltages measured relative to the CT.
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- Wisconsin
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- PE (Retired) - Power Systems
I cannot believe you are saying that at any single point in time, the actual current in 1/2 of a transformer winding is 'out of phase' with that in the other 1/2.
Are you basing your position on work by Faraday, Lentz or maybe Fleming? Is there an IEEE or ANSI ideal, or fundamental, transformer model that I should be looking at?
I am not talking about models. I have repeatedly stated that there are different models which are equivalent.
For several threads and dozens of posts I have focused my discussion on a single core transformer. I have stated my choice to relate secondary voltage 'directions' to that of the singel primary.
Jim, with all due respect, you ignored my question.
Jim, didn't say that. In doing loop analysis, one may not know the sense of the unknown currents. If one chooses wrong, the value comes out negative.
Of course in this case we know the direction of the current and would choose the sense accordingly.
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- Wisconsin
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- PE (Retired) - Power Systems
How many more times are you going to answer questions about current flow in transformers with statements about V(+ to -) being the 'opposite of' V(- to+)?
For this thread i am focusing on currents.
I am not asking about a mathematical loop analysis based on arbitrarily assigned current directions.
I am asking about the currents in the windings of a real world single core transformer with a single primary winding.
What is the relationship of the currents in winding A and in winding B, if the two windings can be connected both in parallel or series?
Ideally, the answer should not depend on if a neutral point is used or not, as electricians run into this situation when using 'buck-boost' connections.
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- Wisconsin
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- PE (Retired) - Power Systems
I have been trying to keep this thread to currents.
If the current is flowing out of terminal L1 then it is in the direction n->L1, and if it is flowing into terminal L2 then it is in the direction of L2->n, giving a winding direction of L2->L1.
Never had a quarrel with you on the directions of the real currents, but I guess I will have to answer my own question.
If V1 = 120V@0 and I1 flows outward, then if I2 flows inward, V2 must be 120V @ 180. Makes sense to me.
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