3 Phase Current Flow

[Besoeker]

'Out of phase' is usually associated with 180 degree phase difference.

Really??????
How would you describe the relationship between the voltage and current in a cage induction motor?
As they are not in phase, aren't out of phase with each other?

 

[mivey]

Depends on who's the master. Could just as easily be A is 0, B is -120, and C is -240...

As long as the rotation and angle differences stay the same, and they do: -120 = 240 and -240 = 120.

 

[Sahib]

Really??????
How would you describe the relationship between the voltage and current in a cage induction motor?
As they are not in phase, aren't out of phase with each other?

See post #20.

 

[Besoeker]

See post #20.

Your point?

 

[Sahib]

Get rid of 'out of phase' and simply state phase difference is so and so, when the phase difference is other than 180 degree.

 

[Besoeker]

Are we on the same planet???

If what you say is the usual interpretation where you are from, we are definitely world's apart.

I think the Maharajah is confusing anti-phase with out of phase.

 

[Smart $]

As long as the rotation and angle differences stay the same, and they do: -120 = 240 and -240 = 120.

Absolutely

 

[Smart $]

I think the Maharajah is confusing anti-phase with out of phase.

There is definitely some confusion somewhere :happyyes:

 

[mivey]

Will you please quote any para from technical literature? I do not remember seeing one such.

There are thousands. Search electrical, engineering, and physics texts and you will find all you want. Croft's Electrician Handbook was next to me on my shelf so:
"117. A three-phase current consists of three different alternating currents out of phase 120 degrees with each other."

Also,
IEEE Dictonary
"Magner
(3) The product of voltage and the component of alternating current that is 90 degrees
out of phase with it. In a passive network reactive power represents the energy that is exchanged alternatively between a capacitive and an inductive storage medium."

"out-of-phase (as prefix to a characteristic quantity)
A qualifying term indicating that the characteristic quantity applies to operation of the circuit breaker in out-of-phase conditions."

"out-of-phase conditions
Abnormal circuit conditions of loss or lack of synchronism between the parts of an electrical system on either side of a circuit breaker in which, at the instant of operation of the circuit breaker, the phase angle between rotating phasors representing the generated voltages on either side exceeds the normal value and may be as much as 180 degrees (phase opposition)."

"reactive power
(2) The product of voltage and out-of-phase component of alternating current. In a passive network, reactive power represents the alternating exchange of stored energy (inductive or capacitive) between two areas. See also: magner."

 

[mivey]

In technical literature, 'Out of phase' is usually followed with 180 degree phase difference...At least that is the way I remember.

Time to brush up.

 

[weressl]

'Out of phase' is usually associated with 180 degree phase difference.

Here he goes, teaching a Brit of the correct use of English.........:rotflmao:

....and no it does not mean that. Not in the US, not in England, not in Germany, not in Hungary, not in Russia, not anywhere in the technical world. One degree of phase angle difference IS 'out of phase'.

 

[weressl]

Greetings Everyone.


when we have a balanced 3Ph system( STAR or WYE), each phase draws the same amount of current and the neutral current provides the return path.

In the case of a balanced load, there is no current flow in the neutral, hence the world balanced.

 

[Besoeker]

Here he goes, teaching a Brit of the correct use of English.........:rotflmao:

Well, given that I'm not English........

....and no it does not mean that. Not in the US, not in England, not in Germany, not in Hungary, not in Russia, not anywhere in the technical world.

And not even in Jockland......

One degree of phase angle difference IS 'out of phase'.

I think Mivey did a good job on that with the references.

Anyway, how are you doing? Been no updates that I've seen recently.

 

[charlie b]

So what you are saying is the current that is flowing through phase A will return back via phase B & C. is it so?. If thats the case, then dont u think that the return current will be opposing the incoming currents in phases B & C.

No. The current that left the source on phase A, and that is returning to the source on phases B and C will not be opposing some other current that is incoming on phases B and C. It is one and the same current. For example, at the moment phase A is at its maximum positive value, the currents in phases B and C will be at negative values, somewhat below their maximum negative value. So at that moment it is one current traveling away from the source and two currents returning to the source.

You can see this in the graph in post #12. When the red line is at a positive peak, the blue and green lines are at negative values.

 

[ggunn]

'Out of phase' is usually associated with 180 degree phase difference.

Out of phase means anything that is not in phase, and to refer to polarity reversed as "out of phase" or "180 degrees out of phase" in waveforms more complex than a sine wave, although common, is technically incorrect.

 

[Smart $]

...

You can see this in the graph in post #12. When the red line is at a positive peak, the blue and green lines are at negative values.

...and equal to exactly half the red line's negated value at that instance, making the sum of all three currents zero. The exact opposite occurs when the red line is at its maximum negative value.

Draw a vertical line through the graph at any instance, and the sum of the values at that instance will be zero, as Besoeker mentioned previously.

 

[kwired]

...and equal to exactly half the red line's negated value at that instance, making the sum of all three currents zero. The exact opposite occurs when the red line is at its maximum negative value.

Draw a vertical line through the graph at any instance, and the sum of the values at that instance will be zero, as Besoeker mentioned previously.

Is it too soon for the OP to introduce non linear loads to the discussion?

 

[Smart $]

Is it too soon for the OP to introduce non linear loads to the discussion?

Just my guess... YES. JMO, but I think unbalanced and/or loads with same ampere values but different power factor should precede a non-linear load discussion.

 

[LightVolt]

The fundamental understanding here is that the neutral is a balancing leg, similar to the current carrying conductors in AC. So, one hot leg cannot conduct current by itself without a "pressure relief valve" so to speak. Within each 1/60 of a second, the amount of current in protons flowing to the load will symbiotically produce the same amount of electrons flowing back to the source.

It is the instantaneous phase angle within the rotation of the sine wave(s) that determines which phase sees peak Voltage and then peak Current. So in a Delta, as phase A is conducting nominal current, Phase B and Phase C share the return path for electrons. Depending on rotation, one will lead the other. In a Wye, the neutral will pick up the additional imbalance if B or C will need to draw more than A. Moreover, imbalanced 3Ph contains single and split phase loads that utilize the neutral. So neutral currents can be calculated and wire sized accordingly.

So in Solar for instance, a 3Ph solar subpanel composed of split phase Inverters will need a neutral sized to carry the imbalance. As the neutral is typically for measurement purposes only per UL1741, this becomes a moot point. This can get more complicated if we add 1Ph Inverters and 3Ph Inverters into the mix. Then it is best practice to add the total of 1Ph Neutral current and any additional imbalance into the neutral sizing. A neutral sized to the same as the EGC from the solar subpanel should satisfy the most critical inspectors or engineers, in almost all scenarios.

 

[kwired]

The fundamental understanding here is that the neutral is a balancing leg, similar to the current carrying conductors in AC. So, one hot leg cannot conduct current by itself without a "pressure relief valve" so to speak. Within each 1/60 of a second, the amount of current in protons flowing to the load will symbiotically produce the same amount of electrons flowing back to the source.

It is the instantaneous phase angle within the rotation of the sine wave(s) that determines which phase sees peak Voltage and then peak Current. So in a Delta, as phase A is conducting nominal current, Phase B and Phase C share the return path for electrons. Depending on rotation, one will lead the other. In a Wye, the neutral will pick up the additional imbalance if B or C will need to draw more than A. Moreover, imbalanced 3Ph contains single and split phase loads that utilize the neutral. So neutral currents can be calculated and wire sized accordingly.

So in Solar for instance, a 3Ph solar subpanel composed of split phase Inverters will need a neutral sized to carry the imbalance. As the neutral is typically for measurement purposes only per UL1741, this becomes a moot point. This can get more complicated if we add 1Ph Inverters and 3Ph Inverters into the mix. Then it is best practice to add the total of 1Ph Neutral current and any additional imbalance into the neutral sizing. A neutral sized to the same as the EGC from the solar subpanel should satisfy the most critical inspectors or engineers, in almost all scenarios.

In first paragraph, I hope you meant electrons where you said protons.

The neutral only picks up imbalance current where the loads are line to neutral loads, if the loads are line to line and are not even load per phase then currents will be unbalanced accordingly.