AC Vectors ?
AC Vectors ?
(OP)
Why do the voltage vectors rotate 180 deg. when the ground is moved from the neutral to say phase 2. This is for wye connected phases??? Can't seem to wrap my head around this one. Thanks.
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RE: AC Vectors ?
RE: AC Vectors ?
Chances are, though, if you do this, you will answer your own question.
RE: AC Vectors ?
then Vab = V at 0 , Vbc = V at -120, Vca = V at 120
if the meter measures voltages to neutral then
Van = Va - Vn
Vbn = Vb - Vn
Vcn = Vc - Vn
now if you ground B phase as is done on open delta PT
Vb = Vn
then
Van = Va - Vb = Vab
Vbn = Vb - Vb = 0
Vcn = Vc - Vb = Vcb = -Vbc so your voltage now appears negative or with a 60 degree phase angle instead of 120 as compared to the phase rotation above
See http://p
RE: AC Vectors ?
Now reverse your meter leads. The voltage will now be -12 volts. The voltage has not changed, nothing has rotated. You have just changed your reference point. Kind of the same for vectors.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: AC Vectors ?
If I measure from A to A', B to B' and C to C' I read 0 vac and 0 deg. difference. AB = 115 vac, BC = 115 vac, AC = 115 vac 120 deg. apart.
After moving the ground to B phase (B') I measure from A to A', B to B' ; C to C' and read 67 vac and 180 deg. difference. The 2nd vector on the right is drawn to show this relationship. Obviously the 2 vectors were equiv. before changing the ground ref.
The ph-ph readings after moving the ground to B'.
AB'= 67 vac, AC'= 136 vac, BC'=67 vac, BA'=180 vac, CA'=136 vac CB'=67 vac. Didn't record angles for these. Some of these make sense but most don't.
I'm getting a headache !
Thanks again.
RE: AC Vectors ?
RE: AC Vectors ?
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: AC Vectors ?
RE: AC Vectors ?
That reverses "B" (rather than rotating it!! Some of us make a distinction). The other issues follow from that.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: AC Vectors ?
The measurements refer to voltage and phase prior to the ground change, and after the ground change. The drawing shows the relationship between the two sources AFTER the ground change since first and second source phases become 180 deg. apart from each other.
Hence, measuring A to A' = 67 vac and 180 deg apart.
Whew ! hope this helps.
Thanks for the responses so far.
RE: AC Vectors ?
Only one additional Q:
Are you have some some secondary load connections to those sources?
Regards.
Slava
RE: AC Vectors ?
Please pay attention. you changed your reference voltage B' and now it's same reference point, as neutral of first source, taht means A-B', C-B' and B-B' now are 67V.
I don't understand 180V, for my pinion is unpossible, max voltages with 180deg is 134V, ( 136V in you post)
RE: AC Vectors ?
Please see attached file, you have noe something like to this.
Regards.
Slava
RE: AC Vectors ?
RE: AC Vectors ?
RE: AC Vectors ?
Slavag can you explain your sketch a little more I am still a bit confused. Are the origonal AB&C vectors 120deg apart. For the second set of vectors I understand that since B is grounded its vector is in the middle of the wye vectors but why are the A' and C' vectors in the direction that they are?
So if I'm understanding all of this correctly, these are two different identical sources with one source gounded at B. We are then measuring between the two sources?
RE: AC Vectors ?
VAC'=133V at -150°
VAB'=67V at -90°
RE: AC Vectors ?
Am I wrong?
Best Regards
RE: AC Vectors ?
Two p0ints I don't understand.
From where angle 101deg and 139.1deg
it's 90deg and 150deg.
It's math, not electricity
Best Regards.
I must say you, I don't know who are you, but with you Im ready make any project.
RE: AC Vectors ?
I also can't figure out your angles.
My convention was to have VBC' be the voltage from C' to B. You seem to have opposite convention which explains some angles. I have referenced horizontal as 0°. You have AB1 at 0°. You have everything tilted 30° compared to Slavag's sketch.
RE: AC Vectors ?
RE: AC Vectors ?
Jghrist, thanks again for your remarks.
Best Regards