No current flow on a balanced neutral?

[gar]

080925-2141 EST

ronaldrc:

Your warm neutral could be a result of a DC flow and a transformer type current probe would not measure this DC, but there will be heat. Use an AC/DC Hall probe with the meter in DC or a real true RMS meter that reads both DC and AC and you could measure the current.

.

 

[quogueelectric]

080917-0929 EST

I will repeat a comment I made in another thread.

If you have a wire of some resistance, meaning not exactly 0, and if the voltage across that wire is exactly 0, then the current thru that wire is exactly 0.

I = V/R = 0/R = 0

In this case there are NOT two currents subtracting from each other.

Change your circuit to two separate neutrals and put a current transformer around the two neutrals. The resultant is a reading of zero. But now you have two separate circuits. Each with the same magnitude of current but out of phase by 180 deg with one another. Thus, canceling each other thru the current transformer.

.

I have been beating this drum for some time good luck while I catch up to this thread.

 

[ronaldrc]

AC or DC does not matter ,I understand a standard clamp on ammeter would not read DC.

The DC circuit I tried to make this illustration with would not prove or disprove if current is flowing. I'm probably not as fast as a lot of you and I had to actually study the circuit before I seen it wouldn't prove anything.

Because the positive current flowing down the neutral conductor in the middle
would flow through the upper diode D1 and through the DC ammeter and meet
its equal and opposite current in the junction of D2 and would null at that point.

 

[gar]

080925-0845 EST

ronaldrc:

My point on DC in the neutral was relative to your comment that someone had a warm neutral and a clamp-on meter read no current.

My comment had nothing to do with your various suggested experiments.

If a wire is warm, then either current is flowing thru the wire, or some other source of energy is feeding the wire to warm it. Like putting a blowtorch at each end of the wire and thermal conductivity allows that heat to move to the middle.

Another experiment for you. One wire with a current flowing thru it, a current probe, and the following two tests:

1. The wire is formed to have a hair pin shape in the middle. The hair pin portion is perpendicular to the long axis of the ends of the wire, and the axis of the current probe is coaxial with the hairpin loop. Maintain this orientation and put the hairpin thru the current probe and the reading will be 0. This is because you have a current flowing thru the current probe in one direction, and an identically equal current but flowing in the opposite direction.

2. Pull the current carrying wire straight and keep the current probe in the same orientation and location relative to the long axis of the wire. Still no current reading, and now there is no current flowing thru the probe.

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[ronaldrc]

Thanks Gar


I might try that expirement later.

Edited to add: Gar your right I did not read your post about the DC current close enough.
But this literature I was reading was about harmonics and I could allmostswear that it was a Mike Holt
article in the Electrical Contractors magizine.

 

[rattus]

Ronald, you can formulate this problem such that the currents appear to flow in the same direction. Does this mean that the neutral current is twice the load current? No, because they are 180 degrees out of phase, so they still cancel.

In short, one of the currents, as defined, will come out to be negative.

 

[ronaldrc]

Rattus

You lost me somewhere, which is not hard to do. Could you explain a little better ?

 

[rattus]

Confucious say:

Confucious say:

Rattus

You lost me somewhere, which is not hard to do. Could you explain a little better ?

Ronald, I will draw some pictures, but give me a little time.

 

[ronaldrc]

Thanks Rattus

I'm in no hurry

 

[rattus]

OK Ronald:

OK Ronald:

Ronald, take a look at the attachment. The currents, I1 and I2 are defined to be CW and CCW respectively, therefore they flow in the same direction in the neutral. Do they add? Don't know yet; let's see.

Clearly the currents are,

I1 = V1/Z1

and,

I2 = V2/Z2

Now, let's look closer at the voltages.

V1 is positive, but V2 is negative, therefore I2 is negative. That means that the I2 really flows in a CW manner so the currents subtract rather than add. This is not uncommon in circuit analysis and is perfectly legal. It is just algebra.

 

[ronaldrc]

Hi Rattus

First off I have to admit to a mistake I have been making in reference to Electrical current flow.

It has been 37 plus years since I have studied Electricity. like a lot in the field I have gotten
Electron flow and conventional flow backwards.

I'm not sure what you are showing in your picture. The bottom half you are showing Electron
flow and in the upper half you are showing conventional flow.

Or are you picturing this as I think you are using the neutral as a common measuring point.

To illustrate the flow of electricity in the single phase of a secondary which we are basing our
discussion on you would use Line #1 as a common test point to see the polarity of the secondary
at any instant in time. And you would leave your one test lead on Line # 1 and move your other lead
to the neutral and then to line #2 for the third measurement.


Electron flow best fits the way we understand electrical flow like in a B+ or a old vacuum tube
power supply the Plate had a positive charge and filament had a minus charge the current flows
from the hot filament toward the Plate which has the positive charge applied to it..

The voltages in the neutral are neither additive or subtractive they will be opposite.they will oppose
each other.That is the reason it works the way it does carrying the unbalanced current.

And if you perfectly balance them they will appear in all respects to all of our testing equipment
and common sense that there is no current flowing and I now believe this as a fact.


Thanks:Ronald

 

[rattus]

Ronald, I am assuming conventional current.

I am trying to show that one can arbitrarily assign current directions on paper. In this case I chose I2 to be backward from reality, and indeed, the currents do add, but they add algebraically.

Since V1 is positive and v2 is negative, the numerical values of I1 and I2 are positive and negative respectively, therefore they tend to cancel each other.

The moral to all this is that the result is the same--just pay attention to the signs.

 

[ronaldrc]

Rattus

I mean no disrespect but I don't understand it. I know we both understand the circuit but I don't understand the math some of us are geared for it and some not, I have learned to live with it.

Thanks

 

[LarryFine]

Ron, to put it simply, he's saying that adding a negative number is the same thing as subtracting a positive number.

10 + (-10) = 10 - 10

 

[winnie]

Just a distantly related side topic:

The 'Large Hadron Collider' generates two beams of protons, running in circles in opposite directions. The storage rings are about 5 miles in diameter, and when running each ring carries a proton current of 0.5A. A single proton will pass the same point about 20000 times per second.

The 'experiments' happen at points where the beams cross. At the point where the beams cross, you have two currents flowing in opposite directions, in the same region of space. The _net_ current at this point is _zero_; you have the same number of protons moving left to right, as right to left. (Well, approximately...the experimenters try to maintain this balance.)

Of course, at this beam intersection, you end up with collisions...and the collisions are where the interesting science (or the end of the earth ) will happen.

-Jon

 

[iwire]

the collisions are where the interesting science (or the end of the earth ) will happen.

LOL, one or the other.

 

[ronaldrc]

What ever: LOL

 

[realolman]

...Of course, at this beam intersection, you end up with collisions...and the collisions are where the interesting science (or the end of the earth ) will happen.

-Jon

I'll bet you 20 bucks the earth doesn't end :smile:

 

[Besoeker]

I'll bet you 20 bucks the earth doesn't end :smile:

But would you be there to collect it?

 

[realolman]

But would you be there to collect it?

Well, yeah,... if it doesn't end.

But he wouldn't if he took the bet and won... that was kinda the point. A feeble attempt at humor.:smile: