How does current flow in a circuit?

[Smart $]

I agree but not a 100 %, three phase circuits can survive without this "other conductor"

Not true. Sure 3? circuits can "survive" without a neutral conductor, but it cannot "survive" with only two conductors (and continue to operate normally).

In a 3? circuit, when current is flowing from source to load on only one conductor, that current is returning (flowing from load) to its source on the other two. As time passes, current will flow from source to load on two conductors, and that current returns (flows from load) to its source on the other one. The preceding process switches to the second and third conductors, respective of timing, returning to the first conductor and repeats for the duration of operation.

 

[Mayimbe]

Not really, because the other two phases act together to comprise the "other conductor".

the three phases act together. Agree

Do you understand how reactive power bounces back and forth between the reactive load component and the source (or PF corrective device, if used)?

I do

The source doesn't have to generate the reactive current, but the system has to carry it, and it does contribute to conductor heating through I^2R losses.

Dont know nothing about reactive current. any reference?? never heard of that. Is it the imaginary part of the phasor current??
Reactive current contribute to conductor heating?? what should I understand you are triying to say by this statement? that Q power creates heating on the conductor?? thats new for me. any reference??

Not true. Sure 3? circuits can "survive" without a neutral conductor, but it cannot "survive" with only two conductors (and continue to operate normally).

In a 3? circuit, when current is flowing from source to load on only one conductor, that current is returning (flowing from load) to its source on the other two. As time passes, current will flow from source to load on two conductors, and that current returns (flows from load) to its source on the other one. The preceding process switches to the second and third conductors, respective of timing, returning to the first conductor and repeats for the duration of operation.

I will say this is true for me only on the transient period. I dont believe that happens on the permanent period. Since in that period the sum of all currents at any time is zero. When I said 3 phase circuits I though that was clear that they have 3 conductors. not two, as you say. Obviously they cannot survive with 2 conductors, since its a 3 phase circuit. If you can find a reference where it says all that you have said about current flowing from load to source, on normal operation, it will be very good to see whats your point.

 

[mivey]

As I said, for static phasor analysis, adopting a positive-negative convention is unnecessary. Each branch current associated with a node has both current flowing into and out of the node (just not at the same time ...and except when the branch current is zero). A [positive-value-only] magnitude coupled with a phase angle describes this current [waveform] without using a positive-negative convention. You have yet to convince me otherwise.

Oh no you don't. It was not about using a negative sign vs a positive magnitude. Adding 180 degrees accomplishes the same thing and gives you a positive magnitude. It was about the choice of current reference directions.

We can pick the current reference directions and they can be into or out of the node. The sign at the end of the analysis will tell us the actual direction of current flow. Your error was stating that there was only one correct way to state KCL when there are three ways.

Like I said, we could give you quotes and references all day. While I do not have a copy of Kirchhoff's original work (it would have to be translated for me), I have given you Maxwell's statement of KCL. I have also given you quotes from recent references. There are many books on electromagnetics, circuit & filter theory, etc. that will tell you the same thing. But you would refuse to hear them and for that I have no cure for your ills.

I guess the only option you have left is to be bored through the ear and resign yourself to the servitude of using a single KCL equation.:grin:

 

[mivey]

Maybe it is, but let me say that in spanish with call it "the negative semicycle" and I think its more accurate, since semi is a prefix that denotes the half of something. And a negative cycle is always negative at all times at any milisecond.

Yes. I should have said 1/2 cycle. Typo on my part.[/quote]

 

[mivey]

when you say that in a pure reactive load, power is flowing in for 1/2 cycle, what kind of power do you mean?? Reactive Power??

Well of course reactive power. What else would a pure reactive load draw?

You have to specify what kind of reactive load are we talking, is it inductive o capacitive?? it matters.

Inductive or capacitive makes no difference. They both exchange reactive power.

In both cases for me, these pure reactive loads are consuming current.

I get consuming power. What do you mean by consuming current?

The current does change the direction, but it "flows from the source to the load". The first time that I have heard the opposite was here.

Please draw a diagram of a generator with two-wire conductor attached to a resistor. Pick a point in time where current is flowing. What direction is the current flowing in wire #1? What direction is current flowing in wire #2?

A source, its an energy active entity, it CAN deliver energy.

A load, its an energy pasive entity, it CAN NOT deliver energy. For long periods of time, eternity.

I can understand the energy premise if you are saying the load & source keep swapping rolls based on the direction of power flow.

since that in electricity, the only way to deliver energy to others its through the current, how can the current flow from the load to the source???

Current flows from a high potential to a low potential. It does not care which is the source and which is the load.

Call a wire a perfect conductor and tie it across the source terminals. Current flows from "+" to "-". Now put a resistive load in the middle of the wire. Current flows from "+", to the resistor, through the resistor, and back to the "-" terminal. The flow from the resistor to the "-" terminal is current flowing from the load to the source.

 

[neutral]

Well I'm still baffled, What week in Electrican or Electronic school did they present this material? I'm glad I didn't have to know all this to repair complex controls and machines for 30+ years. Maybe wiring a house is more complicated than I thought. I think I will pick up another book one thats more up todate next time I go to the store and study up some.

 

[mivey]

Dont know nothing about reactive current. any reference?? never heard of that. Is it the imaginary part of the phasor current??
Reactive current contribute to conductor heating?? what should I understand you are triying to say by this statement? that Q power creates heating on the conductor?? thats new for me. any reference??

I think he means the current associated with pushing reactive power up & down the line. To deliver the reactive power, some extra current is needed to overcome the wire resistance. This results in real power losses in the wire (heating).

 

[mivey]

Well I'm still baffled, What week in Electrican or Electronic school did they present this material? I'm glad I didn't have to know all this to repair complex controls and machines for 30+ years. Maybe wiring a house is more complicated than I thought. I think I will pick up another book one thats more up todate next time I go to the store and study up some.

I never went to Electrician or Electronic school so I'm not sure how much material you covered and what material they did not teach you. Also, we rarely get to experience everything in our careers so you may never have had to worry about some details.

If there is an engineering school nearby, or a library with a good technical section, you should be able to find more to read on the subject than you can probably stand.

I'm not sure I can, but let me see if I can give you a pseudo-example that might make sense to you. You mentioned you have controls experience. You can pick your relay polarity so you get a clockwise needle deflection for current in either direction you choose.

Smart $ is essentially saying that there is a universal constraint on the directions you choose and that only one way is right. I'm saying you can choose the direction in any way that fits what you are wanting to do.

 

[rattus]

Agreed:

Agreed:

Smart $ is essentially saying that there is a universal constraint on the directions you choose and that only one way is right. I'm saying you can choose the direction in any way that fits what you are wanting to do.

One can point the arrows anyway one wishes. Just keep the phase angles correct. Then you add the values of the in arrows and subtract the values of the out arrows, or vice-versa. Any Freshman engine student can do it.

 

[mivey]

One can point the arrows anyway one wishes. Just keep the phase angles correct. Then you add the values of the in arrows and subtract the values of the out arrows, or vice-versa. Any Freshman engine student can do it.

I would hope so. I would have thought the same would be true for an electronic student. May or may not be the case with an electrician course. I know some linemen schools cover the basics of these concepts but I am pretty sure it goes over a lot of the linemen's heads (from what I've seen).

 

[mivey]

man now this is good and we all most went to quantum physics as well. I think we could swing the pendulum so quantum physics slide into this as well since we talking timing.

Well, since you asked. :grin:

It is really quite interesting that in quantum physics, particles actually do move in two different directions at the same time. For starters, read some of the articles concerning physicist Richard Feynman's idea of "quantum walks".

It is more than just hocus-pocus as they have been able to physically produce the theoretical behavior using cesium atoms.

 

[Smart $]

...

I will say this is true for me only on the transient period. I dont believe that happens on the permanent period. Since in that period the sum of all currents at any time is zero. When I said 3 phase circuits I though that was clear that they have 3 conductors. not two, as you say. Obviously they cannot survive with 2 conductors, since its a 3 phase circuit. If you can find a reference where it says all that you have said about current flowing from load to source, on normal operation, it will be very good to see whats your point.

Set up an experiment with a 3? source and load... and of course 3 conductors. In each of the 3 conductors insert an ammeter biased with negative to the source an positive to the load. Energize the system and take a plethora of instantaneous readings at regular intervals during at least the first cycle of current. If we choose to use the negative to positive current flow convention, when an ammeter is reading positive, current is flowing from the source to the load, and conversely when an ammeter is reading negative, current is flowing from the load to the source.

The above is regarding the pure physics of the system. Now when you enter the realm of mathematical analysis you have to choose to include direction or adopt the positive-negative convention as a substitute for direction. Under the former premise, it is obvious all currents do not flow from source to load. Under the latter, you can say all currents all currents flow from source to load because you have adopted an extra convention which permits you to do so.

 

[Smart $]

Smart $ is essentially saying that there is a universal constraint on the directions you choose and that only one way is right. I'm saying you can choose the direction in any way that fits what you are wanting to do.

One can point the arrows anyway one wishes. Just keep the phase angles correct. Then you add the values of the in arrows and subtract the values of the out arrows, or vice-versa. Any Freshman engine student can do it.

Quite easy to do for DC, but the arrows change direction and magnitudes vary in AC circuit analysis.

Mivey, this universal constraint you speak of is only in your mind. I have stated no such thing. Under a particular mode of mathematical analysis I stated adopting the positive-negative convention is unnecessary. Quit stretching my words to mean something else.

 

[mivey]

Set up an experiment with a 3? source and load... and of course 3 conductors. In each of the 3 conductors insert an ammeter biased with negative to the source an positive to the load. Energize the system and take a plethora of instantaneous readings at regular intervals during at least the first cycle of current. If we choose to use the negative to positive current flow convention, when an ammeter is reading positive, current is flowing from the source to the load, and conversely when an ammeter is reading negative, current is flowing from the load to the source.

That would be using electron flow notation. Thanks to Ben Franklin, the other way is called conventional flow notation and uses hole flow. We are taught both, but the conventional notation is used in most electrical engineering texts. Either one works fine although electron flow might make more sense when studying the motion of electrons.

The above is regarding the pure physics of the system. Now when you enter the realm of mathematical analysis you have to choose to include direction or adopt the positive-negative convention as a substitute for direction.

We are fishing from the same boat here.

Under the former premise, it is obvious all currents do not flow from source to load. Under the latter, you can say all currents all currents flow from source to load because you have adopted an extra convention which permits you to do so.

Again, we must distinguish between the physical world and the way we measure the physical world.

Quite easy to do for DC, but the arrows change direction and magnitudes vary in AC circuit analysis.

We use instantaneous currents. In relaying and power systems, it is common to look at the current direction to be direction of flow in the positive 1/2 cycle using conventional notation.

Mivey, this universal constraint you speak of is only in your mind. I have stated no such thing. Under a particular mode of mathematical analysis I stated adopting the positive-negative convention is unnecessary. Quit stretching my words to mean something else.

Then I failed to see your point. In post #82 you assert that of the three ways to state KCL, only one is correct. By saying that two of the three representations of KCL are wrong, you are constrained to using only the remaining one.

Perhaps the appearance of your supporting and then un-supporting certain conventions clouded your points. I am now thinking one of your points must be that when using vector notation, your measurements should always be based on all of the currents flowing in the same sense relative to the node?

You start out supporting the equation that sums all currents entering a node (could also be summing all currents leaving a node): From #17: "The true vector base formula is Ia + Ib + Ic + In = 0". This equates to all of the meters having the same reference direction relative to the node.

In post #48 you seem to say that there is something wrong with choosing arrows in an opposing direction (the same as using a negative sign): "To write your form of the equation, you have to adopt the convention that all currents flowing into a node are positive and all current flowing out of the node are negative. I refuse to adopt any convention that is totally unnecessary." Then your own diagram in post #59 shows an adoption of both methods.

You show one system supporting the method of assuming positive flow for all currents leaving a node. All of the arrows face away from node 2 and show a positive needle deflection. To be clear, this is positive for leaving, negative for entering (In + I1 + I2 +I3 = 0)

You also show a system supporting the other convention. The three arrows associated with the phase currents face away from node 1 and show a positive needle deflection for current leaving. The neutral shows a negative deflection for current leaving (In = I1 + I2 + I3).

You also state there is no need to decide whether or not current is entering or leaving. The way you connect your meters makes those very assumptions. It matters a whole lot if you are feeding these currents into a relay as you may have to pick a positive or negative deflection for the instantaneous current leaving a node. Reversing the meter leads adds a negative sign (i.e. adds 180 degrees).

There is not some amorphous equation out there for a particular node under inspection. To inspect or analyze the system, we must choose some sign conventions and one method is not always better than the other.

 

[Mayimbe]

I get consuming power. What do you mean by consuming current?Please draw a diagram of a generator with two-wire conductor attached to a resistor. Pick a point in time where current is flowing. What direction is the current flowing in wire #1? What direction is current flowing in wire #2?

consuming current = consuming power (in my mind)

Its drawn.

Its picked.

in wire #1 we have the current flowing from the generator to the source sir.

in wire #2 we have the current flowing from the resistor to the generator sir.

conclusions:

None. I have failed to achieve one.

Call a wire a perfect conductor and tie it across the source terminals. Current flows from "+" to "-". Now put a resistive load in the middle of the wire. Current flows from "+", to the resistor, through the resistor, and back to the "-" terminal. The flow from the resistor to the "-" terminal is current flowing from the load to the source.

From this statement "Call a wire a perfect conductor and tie it across the source terminals" im understanding to put the source in shortcircuit. the current will tend to infinity. Or nothing would happen, there will be no current. Since V+ = V-. Ok same as before, the current is flowing from the resistor to the source. And from the source to the resistor. Same conclusions. None

Dont you agree that in both examples, wire # 2 its a imperative condition for a electric circuit to exist??

Its funny that everybody its putting diferents scenarios to stand their view. If you tell me a reference where it has a whole chapter or section of his book or paper saying that the current flows from the load to the source at normal conditions. I'll be pleased to read it.

I think he means the current associated with pushing reactive power up & down the line. To deliver the reactive power, some extra current is needed to overcome the wire resistance. This results in real power losses in the wire (heating).

I have never heard such thing. From where is coming this "extra current"??
Dont see the point here.

As before

give me a reference => I'll read it=> get conclusions. Then it can happen 3 things. the reference says im wrong or you are wrong. Or we both wrong, which would be funny

Otherwise, you can quote me some people saying this things, like you did with Smart $, with maxwell and all those guys.

Set up an experiment with a 3? source and load... and of course 3 conductors. In each of the 3 conductors insert an ammeter biased with negative to the source an positive to the load. Energize the system and take a plethora of instantaneous readings at regular intervals during at least the first cycle of current. If we choose to use the negative to positive current flow convention, when an ammeter is reading positive, current is flowing from the source to the load, and conversely when an ammeter is reading negative, current is flowing from the load to the source.

I set it up on MATLAB. Its much comfortable that finding all this equipment that you mentioned. Hope you understand.

First cycle of the current. Transient period. Agree with all you said.

The above is regarding the pure physics of the system. Now when you enter the realm of mathematical analysis you have to choose to include direction or adopt the positive-negative convention as a substitute for direction. Under the former premise, it is obvious all currents do not flow from source to load. Under the latter, you can say all currents flow from source to load because you have adopted an extra convention which permits you to do so.

OK. Do you have an extra convention adopted that permits you to say the oppossite that my convention adopted do???

 

[mivey]

consuming current = consuming power (in my mind)

O.K. I guess you could adopt that way of thinking and I see what you are thinking.

Ok same as before, the current is flowing from the resistor to the source.

Wonderful. Now adopt the idea that the source is called the source and the resistor is called the load. Now you have current flowing from a load to a source. Now you should be able to see what we are saying.

Dont you agree that in both examples, wire # 2 its a imperative condition for a electric circuit to exist??

Yes. You must have a complete path.

Its funny that everybody its putting diferents scenarios to stand their view. If you tell me a reference where it has a whole chapter or section of his book or paper saying that the current flows from the load to the source at normal conditions. I'll be pleased to read it.

Maybe that won't be necessary. See the adoption statement above.

I have never heard such thing. From where is coming this "extra current"??
Dont see the point here.

Consider the current feeding a motor. Some of the current is used to provide useful work. Some of the current is used for creating and maintaining the magnetic field in the motor and is not used to provide real work and is the "reactive current" as Larry called it.

If we had a perfect conductor, the "reactive current" would be all the current needed to supply the reactive power. Since we have wire resistance, there is even more current needed to overcome the wire resistance and get the reactive power delivered to the motor. This is what I labeled "extra current".

Larry's point was that pushing reactive power up and down a wire also produces heat loss in the wire.

 

[neutral]

So, which came first the chicken or the egg?

 

[mivey]

So, which came first the chicken or the egg?

The one on the appetizer menu.

 

[Smart $]

That would be using electron flow notation. Thanks to Ben Franklin, the other way is called conventional flow notation and uses hole flow. We are taught both, but the conventional notation is used in most electrical engineering texts. Either one works fine although electron flow might make more sense when studying the motion of electrons.

We are fishing from the same boat here.

Again, we must distinguish between the physical world and the way we measure the physical world.

We use instantaneous currents. In relaying and power systems, it is common to look at the current direction to be direction of flow in the positive 1/2 cycle using conventional notation.

I concur with your conclusions.

Then I failed to see your point. In post #82 you assert that of the three ways to state KCL, only one is correct. By saying that two of the three representations of KCL are wrong, you are constrained to using only the remaining one.

By that point in the discussion, I thought for sure you would know I was implying that only one of the three methods is correct without adopting the positive-negative convention, or should I be more technical and say the one correctly written method includes the stipulation it uses the positive-negative convention. Without the stipulation those interpretting the the other two ways may or will be confused...

When entering or leaving or their synomyms are used, the stated form of the equation can be interpretted as omitting the opposite going currents from the summing operation... and as such, the [sum] total will not equal zero. Example: A node has 6 branches, 4 of which are conducting current flowing into the node while 2 have current flowing out of the node. Not knowing the positive-negative convention has been adopted for the other two methods, one would [tend to] think they should only sum the currents of the 4 branches with current flowing into the node when they choose to use the stated version using the word "entering".

Perhaps the appearance of your supporting and then un-supporting certain conventions clouded your points. I am now thinking one of your points must be that when using vector notation, your measurements should always be based on all of the currents flowing in the same sense relative to the node?

Not really. But I'm sensing your mind's eye is a bit more open ...

First, when we use static phasor analysis for the currents, our magnitudes are always positive due to using the rms value (sure you can negate it and use a 180? phase angle shift if you want... but that too is unnecessary ). Then we associate a cyclic angle with our rms value to specify a point in cycle timing that represents the positive peak of the waveform (again we can use a negative angle if we want, but this too is unnecessary as all angles could be stated as positive less than 360? too, due to the cyclic nature of the beasty ). The two values interassociated describe the waveform. Using vector addition the summing of all currents associated with a node yields a result of zero. No ingoing outgoing methodology to adopt or stipulated

You start out supporting the equation that sums all currents entering a node (could also be summing all currents leaving a node): From #17: "The true vector base formula is Ia + Ib + Ic + In = 0". This equates to all of the meters having the same reference direction relative to the node.

In post #48 you seem to say that there is something wrong with choosing arrows in an opposing direction (the same as using a negative sign): "To write your form of the equation, you have to adopt the convention that all currents flowing into a node are positive and all current flowing out of the node are negative. I refuse to adopt any convention that is totally unnecessary." Then your own diagram in post #59 shows an adoption of both methods.

You show one system supporting the method of assuming positive flow for all currents leaving a node. All of the arrows face away from node 2 and show a positive needle deflection. To be clear, this is positive for leaving, negative for entering (In + I1 + I2 +I3 = 0)

You also show a system supporting the other convention. The three arrows associated with the phase currents face away from node 1 and show a positive needle deflection for current leaving. The neutral shows a negative deflection for current leaving (In = I1 + I2 + I3).

You also state there is no need to decide whether or not current is entering or leaving. The way you connect your meters makes those very assumptions. It matters a whole lot if you are feeding these currents into a relay as you may have to pick a positive or negative deflection for the instantaneous current leaving a node. Reversing the meter leads adds a negative sign (i.e. adds 180 degrees).

There is not some amorphous equation out there for a particular node under inspection. To inspect or analyze the system, we must choose some sign conventions and one method is not always better than the other.

Yada-yada-yada... :roll:

Please revisit diagram of post #59. All ammeters have the arrow pointing away from the node they are associated with. This is the prescribed method for taking measurements. As for the needle deflection in the diagram, that is just the way the circuit program draws an ammeter. All ammeters are identical. It is not representive of the actual current flow.

The multitude of positive and negative readings on the ammeter does not matter, because in static phasor analysis we don't use the plethora of instantaneous readings, per se, but rather two values which describe the waveform throughout a single and repititions of the cyclic period.

In conclusion (I hope ), there is no one best method. I made a modest and simple comment that has blown up into a technobabble nightmare

 

[Mayimbe]

O.K. I guess you could adopt that way of thinking and I see what you are thinking.Wonderful. Now adopt the idea that the source is called the source and the resistor is called the load. Now you have current flowing from a load to a source. Now you should be able to see what we are saying.Yes. You must have a complete path.Maybe that won't be necessary. See the adoption statement above.Consider the current feeding a motor. Some of the current is used to provide useful work. Some of the current is used for creating and maintaining the magnetic field in the motor and is not used to provide real work and is the "reactive current" as Larry called it.

Really?? You just have make to adopt a condition, and you didnt ask me If I was agree with that. Despite this fact, I dont know why but I got strange feeling about that...

Considered. some current goes with P and some other goes with Q, agree. Oh ok, reactive current, I had the believe they were the same thing ("reactive" current and "active" current), I guess I should send some emails for lots of people in the field that didnt know about this. If we keep creating things out of nowhere we will get to a new engineer as well... just saying...

If we had a perfect conductor, the "reactive current" would be all the current needed to supply the reactive power. Since we have wire resistance, there is even more current needed to overcome the wire resistance and get the reactive power delivered to the motor. This is what I labeled "extra current".

Larry's point was that pushing reactive power up and down a wire also produces heat loss in the wire.

same as above. why stand and defend on larrys point if you know that deep down, you know theres something strange and messy about the whole "reactive current" idea?

quit labelling things without a criteria. "extra current" mislead to many things, and none of them was the one I figured you tried to say the first time. How I could possibly known what you were triying to say??