2 Phases of a 3 Phase System
- Thread starter Fitzdrew516
- Start date
- Status
To have two phasors requires three wires.
Uber technically, to establish a phase requires at least two instances. Once established—and maintained—it is a phase at any given instant.
What about 2 line currents? ia/0 and ib/120
a phasor can be v, i, S
to MEASURE 2 v phasors you need 3 points
isn't phase angle the arctan(img/real) at any given point in time?
mivey
Senior Member
The phase still needs a reference if you want to quantify the value.
No. Arctan will not distinguish all four quadrants.
How are you going to get two line currents with less than three wires?
I'm uncertain what you are asking here. Thus I answer with a question....
How does one determine imaginary and real values with one sample?
That's analogous to being given the length of a right triangle's hypotenuse and asked to provide the length of the legs without any additional information.
mivey
Senior Member
Suppose you meant to say arctan2, which solves the quadrant problem and the divide by zero problem. You are still using a reference because the axis is not a given. You can't assume a starting point on the signal, you have to specify a starting point and that my friend is specifying a reference.
Wasn't that the simple original point rather than the convoluted mess that others have made it?
Shouldn't that be fewer than three wires?
I already stated one signal can serve as a reference to the other. The resulting Lissajous figure shape depends on the phase shift between the two signals and so may be used to measure that phase shift.
But whether that phase shift is 120 degree or not in the present Dennis case remains to be confirmed.
- Location
- Massachusetts
"fewer than three wires" = "less than three wires"
...or are we talking proper English? You would be correct according to some. But AFAIK it is not an etched-in-stone rule. I think it is just a rule some writers made up just to see how many they could get on board.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
mivey
Senior Member
Yes.
mivey
Senior Member
Correct, at minimum a third conductor is needed. The neutral is just a grounded conductor and provides the third conductor needed.
It's just that the name "two phase system" is reserved for the system with a 90 degree difference.
I think it has only historical significance.
Technically speaking, two phases with 120 degree phase difference would also create a rotating magnetic field unaided.
Is it inferior to that created by two phases with 90 degree phase difference?
mivey
Senior Member
An "unaided" rotating field requirement of some specified quality or characteristic can be added for an application if so desired. It has nothing to do with the fundamental existence of a phase difference between two signals.
Not all multi-phase applications require rotation but for applications that depend on a rotating field, the type and characteristics can be important.
No. Just correct.
The OP is about just two conductors.
- Status