sparks1
Senior Member
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- Massachusetts
What happens to the neutral current when it returns back to the power station on the negative half cycle?
Neutral current
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Re: Neutral current
You may be visualizing current like water flowing through a pipe. Thats a good way to learn about circuits, but (like everything) it is really a simplified explination. It seems like the water (or current) is building up somewhere.
For DC circuits, the electrons (that is the current) go in a complete loop. (Its one way to look at Kirchoffs current law). If the circuit is powered by a battery, the electrons flow from the negative plate through the circuit and to the positive plate. Inside the battery, the electrons basically move from the positive plate to the negative plate. Thus, they are always moving in a complete loop, and they don't build up anywhere.
For the water analogy, you might picture a garden hose going in a complete circle with a pump in it. The hose is full of water, and once the pump starts, all the water has to move at the same rate at the same direction.
Now if we talk about AC circuits, the electrons don't really move very far. Once they start going one direction, the voltage turns around, and reverses them. So for the garden hose, just picture the water moving a little bit one direction, and then turning around and going the other way.
Hope that helps a little:
Steve
You may be visualizing current like water flowing through a pipe. Thats a good way to learn about circuits, but (like everything) it is really a simplified explination. It seems like the water (or current) is building up somewhere.
For DC circuits, the electrons (that is the current) go in a complete loop. (Its one way to look at Kirchoffs current law). If the circuit is powered by a battery, the electrons flow from the negative plate through the circuit and to the positive plate. Inside the battery, the electrons basically move from the positive plate to the negative plate. Thus, they are always moving in a complete loop, and they don't build up anywhere.
For the water analogy, you might picture a garden hose going in a complete circle with a pump in it. The hose is full of water, and once the pump starts, all the water has to move at the same rate at the same direction.
Now if we talk about AC circuits, the electrons don't really move very far. Once they start going one direction, the voltage turns around, and reverses them. So for the garden hose, just picture the water moving a little bit one direction, and then turning around and going the other way.
Hope that helps a little:
Steve
sparks1
Senior Member
- Location
- Massachusetts
Re: Neutral current
Steve ,
I don't know why I was thinking that the current would go somewhere. In fact, it is just alternating back and forward. It's that AC time domain, phasor problem, again that keep coming up in my mind from previous posts.
I think I need some coffee!
Steve ,
I don't know why I was thinking that the current would go somewhere. In fact, it is just alternating back and forward. It's that AC time domain, phasor problem, again that keep coming up in my mind from previous posts.
I think I need some coffee!
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Re: Neutral current
sparks1,
I wonder if part of your question centers on the fact that there is more than one neutral current to think about?
Essentially, (although one can prevaricate a theoretical bit), the neutral current on the secondary side of a single phase transformer stays in the circuit of the single phase secondary out through the conductors to the load. This neutral current doesn't go back to the PoCo.
If the PoCo generator is connected directly to the single phase transformer, (that is, there are no substations or step up transformers in between) then, the current on H2 returns to the PoCo generator. If H2 is connected to the transmission neutral, then that is the neutral current that heads to the generator.
Two seperate systems, even though they are tied to the same conductor running down to the same earth ground connection at the transformer.
sparks1,
I wonder if part of your question centers on the fact that there is more than one neutral current to think about?
Essentially, (although one can prevaricate a theoretical bit), the neutral current on the secondary side of a single phase transformer stays in the circuit of the single phase secondary out through the conductors to the load. This neutral current doesn't go back to the PoCo.
If the PoCo generator is connected directly to the single phase transformer, (that is, there are no substations or step up transformers in between) then, the current on H2 returns to the PoCo generator. If H2 is connected to the transmission neutral, then that is the neutral current that heads to the generator.
Two seperate systems, even though they are tied to the same conductor running down to the same earth ground connection at the transformer.
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Re: Neutral current
A related question to those on the forum who are familiar with the PoCo side of this electrical question. . .
From the PoCo generator to the consumer load. . .how many transformers can be in that transfer of energy?
I know that, theoretically, the number is infinite, and that real world losses make the number finite. Real world costs, it seems to me, impose further limitations. Is there a practical rule-of-thumb or an actual regulation that sets a limit on the number of transformers?
A related question to those on the forum who are familiar with the PoCo side of this electrical question. . .
From the PoCo generator to the consumer load. . .how many transformers can be in that transfer of energy?
I know that, theoretically, the number is infinite, and that real world losses make the number finite. Real world costs, it seems to me, impose further limitations. Is there a practical rule-of-thumb or an actual regulation that sets a limit on the number of transformers?
Ed MacLaren
Senior Member
Re: Neutral current
Sparks1,
Current doesn't "flow through" a transformer.
The primary current flows only in the primary circuit, and the secondary (load) current, including any possible fault current, flows only in the secondary circuit.
The secondary winding is the "source", that Dereckbc referred to above, of the load current.
The first sketch below represents a simple single phase installation, but the principle applies to all transformers except auto-transformers.
As illustrated in the lower sketch, each transformer in an installation actually creates a separate system. (Separately Derived System)
Note - These sketches were originally drawn to illustrate fault current flow, but the same principle applies to unbalanced load (neutral) current.
Ed
[ February 18, 2005, 10:32 AM: Message edited by: Ed MacLaren ]
Sparks1,
Current doesn't "flow through" a transformer.
The primary current flows only in the primary circuit, and the secondary (load) current, including any possible fault current, flows only in the secondary circuit.
The secondary winding is the "source", that Dereckbc referred to above, of the load current.
The first sketch below represents a simple single phase installation, but the principle applies to all transformers except auto-transformers.
As illustrated in the lower sketch, each transformer in an installation actually creates a separate system. (Separately Derived System)
Note - These sketches were originally drawn to illustrate fault current flow, but the same principle applies to unbalanced load (neutral) current.
Ed
[ February 18, 2005, 10:32 AM: Message edited by: Ed MacLaren ]
- Location
- Lockport, IL
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- Semi-Retired Electrical Engineer
Re: Neutral current
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OK. I?ll admit to one of the ?lies? that are part of this description. The number of electrons in motion is a bit higher than the 25, and 50, and 1200 that are cited above. The number is actually closer to a couple of bazzilion. But the concept is reasonably accurate.
Here is how I suggest you think about electron flow in an AC circuit:ASIDE: To all engineers and purveyors of science who are members of this Forum:
I would like to suggest that we collectively pledge never again to discuss herein the notions of ?drift current,? or ?electron drift,? or ?drift velocity,? or any related subject. They constitute a ?truth? that does not help in the understanding of the daily activities of any electrician, contractor, inspector, instructor, maintenance technician, or engineer. Please consider ?drift? to be a ?graduate level? topic, and the Forum to be an ?undergraduate level? environment.
It does not matter that a single electron might only jump to the next atom, and that a different electron continues down the wire. For all practical purposes, it is the same as saying that a single electron travels throughout the entire circuit at nearly the speed of light. In any event, that is how I intend to respond to questions such as this one.
So I beg that no-one feel himself or herself impelled to point out the liesthat I am about to tell.
</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">Early in the positive half cycle, a ?few? electrons (let us say 25) travel, at nearly the speed of light, from the power station, into your house panel, out via a breaker and along a ?hot leg? to the ?hot side? of the plug of your clock radio, through the clock radio and out to the ?cold side? of its plug, via the neutral (?cold leg?) wire back to the panel, and back along the utility wires to the power station. They go through the power station?s generator, and start the same journey all over again. As far as they are concerned, since they cannot predict the future, it will be their fate to continuously travel this round trip forever.</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">A little bit later, still in the positive half cycle, but not yet at the peak of the positive half cycle, the original 25 electrons will be joined by others (let us say 50 more), and they will make the round trip together.</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">As the current continues to rise toward the positive peak, more and more electrons join in, and travel the round trip. At the positive peak current level, you will have a maximum number of electrons (let us say 1,200), going through the entire round trip together.</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">After you pass the peak current, the number of electrons making the round trip starts to get smaller. Just before the current reaches the zero axis, you might see only one electron making the round trip. Then the current reaches zero, and there is no electron motion.</font>
</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">As the current starts in its negative half cycle, a ?few? electrons (let us say 25) travel, at nearly the speed of light, from the power station, but this time along the utility?s neutral conductor, into the neutral bar of your house panel, along the neutral wire into the ?cold side? of the plug of your clock radio, then through the clock radio ?backwards,? then to the ?hot side? of the plug, through the house wires to the main panel, then into the breaker (again, ?backwards?) to the bus bars, out to the utility wires, along the utility?s ?hot wires? to the power station, and into the utility?s generator, again ?backwards.? They will continue in this ?reverse round trip,? for as long as the current is in its negative half cycle.</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">A little bit later, still in the negative half cycle, but not yet at the negative peak, the original 25 electrons will be joined by others (let us say 50 more), and they will make the ?reverse round trip? together.</font>
- <font size="2" face="Verdana, Helvetica, sans-serif">Do I have to continue this description, or can you see what will happen as current reaches its negative peak, then drops to a smaller negative current, then reaches zero current, then starts on the positive half cycle again?</font>
OK. I?ll admit to one of the ?lies? that are part of this description. The number of electrons in motion is a bit higher than the 25, and 50, and 1200 that are cited above. The number is actually closer to a couple of bazzilion. But the concept is reasonably accurate.
sparks1
Senior Member
- Location
- Massachusetts
Re: Neutral current
Ed,
Thanks for the diagrams.
In fact, current is induced in a transformer from the primary to the secondary or it can be the other way I'm sure you are already aware of this. I don't know were "flow through came from". Current flows in the primary as you have stated, but it also is induced into the secondary.Your diagram shows the path that a ground fault current will take to open the secondary fuse.
Most single phase utility transformers for example, don't have secondary protection. If a short circuit develops in the secondary the all likely hood would be that the secondary winding will burn itself clear to open. During this short circuit cycle the short circuit current is induced into the primary. This induced current may never reach a level large enough to open the primary 15 amp fuse due to the ratio of the transformer.
Ed,
Thanks for the diagrams.
In fact, current is induced in a transformer from the primary to the secondary or it can be the other way I'm sure you are already aware of this. I don't know were "flow through came from". Current flows in the primary as you have stated, but it also is induced into the secondary.Your diagram shows the path that a ground fault current will take to open the secondary fuse.
Most single phase utility transformers for example, don't have secondary protection. If a short circuit develops in the secondary the all likely hood would be that the secondary winding will burn itself clear to open. During this short circuit cycle the short circuit current is induced into the primary. This induced current may never reach a level large enough to open the primary 15 amp fuse due to the ratio of the transformer.
sparks1
Senior Member
- Location
- Massachusetts
Re: Neutral current
al hildenrand,
If current is transferred through the primary to the secondary of a tranformer in the positive half cycle of the sine wave then the neutral current passes back through the transformer during the negative half cycle of the sine wave.
al hildenrand,
If current is transferred through the primary to the secondary of a tranformer in the positive half cycle of the sine wave then the neutral current passes back through the transformer during the negative half cycle of the sine wave.
sparks1
Senior Member
- Location
- Massachusetts
Re: Neutral current
Charlie,
I give you an A+ for your decription of Alternating current pathway.
Thank you Sir!
Charlie,
I give you an A+ for your decription of Alternating current pathway.
Thank you Sir!
Re: Neutral current
What Ed said was the diagram was originally used to show fault current. He was using it to show you that we are converting electric energy to magnetic flux and back to electrical energy.
Ed was trying to tell you that the current doesn't flow from the secondary to the primary and back to the generators.
Ronald
What Ed said was the diagram was originally used to show fault current. He was using it to show you that we are converting electric energy to magnetic flux and back to electrical energy.
Ed was trying to tell you that the current doesn't flow from the secondary to the primary and back to the generators.
Ronald
Re: Neutral current
Sparks et al,
I just want to emphasize these points:
1) Current of any kind, AC, DC, or whatever MUST flow in a closed loop.
2) Instantaneous current, i(t), at any instant in time, is the same at all points in the closed loop no matter if it is DC or positive lobe AC or negative lobe AC.
3) An electron flow rate of 0.6x10^19/second is required to produce 1 Ampere.
Sparks et al,
I just want to emphasize these points:
1) Current of any kind, AC, DC, or whatever MUST flow in a closed loop.
2) Instantaneous current, i(t), at any instant in time, is the same at all points in the closed loop no matter if it is DC or positive lobe AC or negative lobe AC.
3) An electron flow rate of 0.6x10^19/second is required to produce 1 Ampere.
sparks1
Senior Member
- Location
- Massachusetts
Re: Neutral current
ronaldc,
I'm well aware of the fact there is no physical connection between the primary and the secondary of a transformer, with the exception of auto transformer. The primary and secondary are magnetically coupled together. Therefore, the current is magnetically induced into the secondary in a step down or step up transformer! This is how the current is transferred.
Neutral current is magnetically induced back into the primary during the negative half cycle back to the Power Co source.
ronaldc,
I'm well aware of the fact there is no physical connection between the primary and the secondary of a transformer, with the exception of auto transformer. The primary and secondary are magnetically coupled together. Therefore, the current is magnetically induced into the secondary in a step down or step up transformer! This is how the current is transferred.
Neutral current is magnetically induced back into the primary during the negative half cycle back to the Power Co source.
al hildenbrand
Senior Member
- Location
- Minnesota
- Occupation
- Electrical Contractor, Electrical Consultant, Electrical Engineer
Re: Neutral current
Charlie B,
While you describe an electron's life in a generator that has an output voltage that is the same as the utilization voltage at the load, the modern AC generator keeps a closer relationship with its electrons, no?? Basically, the electrons from the AC generator go to the transformer yard beside the plant (or inside it) and back to the generator again.
Charlie B,
While you describe an electron's life in a generator that has an output voltage that is the same as the utilization voltage at the load, the modern AC generator keeps a closer relationship with its electrons, no?? Basically, the electrons from the AC generator go to the transformer yard beside the plant (or inside it) and back to the generator again.
sparks1
Senior Member
- Location
- Massachusetts
Re: Neutral current
Rattus,
"All currents at any time are coupled back to the primary".
All currents at any time are coupled back to the primary.There you go now, I said it now! I couldn't agree with you more.
Et al,
If there wasn't any primary voltage and current there wouldn't be any secondary current!
Rattus,
"All currents at any time are coupled back to the primary".
All currents at any time are coupled back to the primary.There you go now, I said it now! I couldn't agree with you more.
Et al,
If there wasn't any primary voltage and current there wouldn't be any secondary current!
sparks1
Senior Member
- Location
- Massachusetts
Re: Neutral current
To the poco via neutral on the negative half cycle.
Rattus,
Please review the post. I was responding to Ed's take on this subject dated Feb 18, 2005. When he said, "The neutral current only flows in the secondary circuit."
Can you give me your opinion on this!
Thanks!
[ February 20, 2005, 08:17 PM: Message edited by: sparks1 ]
To the poco via neutral on the negative half cycle.
Rattus,
Please review the post. I was responding to Ed's take on this subject dated Feb 18, 2005. When he said, "The neutral current only flows in the secondary circuit."
Can you give me your opinion on this!
Thanks!
[ February 20, 2005, 08:17 PM: Message edited by: sparks1 ]
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