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Originally Posted by GoldDigger
See post #6 for how it can be.
I sketched it out
l-n 600/0
the other x/120
the sum (rather than subtract as if pol was reversed) being 200/30

can't find an x that works

2. Gentlemen
and comment back

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he has the same set up on the other sets
n is floating, but the others read ok

has it ever worked correctly?
is it a new install being commissioned?

the only way I can see those magnitudes
l-n ~600
l-n ~ 150 with a 300
is the neut having 600/0 +/- 15-20 deg phasing vs +/- 120 deg
no idea how you would get that

4. Originally Posted by ATSman
Gentlemen
and comment back
Sometimes I wonder if it is worth challenging someone that is so sure of themself. That's why I thought my suggestion was fair earlier too.

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Originally Posted by mrmuneeb
dear All,

Hi, I am having a problem of unbalanced strange values of system voltages in of our power generation plant,
the disturbance in voltage is being reflected on Low voltage side only,

system diagram is attached.

Attachment 20244

what the system must show at low voltage side is;
1. P-P 480V
2.P-N 277V

but the current scenario on delta side of transformer is;

L1-L2= 316 V
L2-L3= 147 V
L3-L1= 221 V

L1-N= 594 V
L2-N= 599 V
L3-N= 530 V

neutral is kept floating on both sides, i.e. both LV & MV neutral is floating.
is there any fault in on of the system phases?
The vector sum of line or phase voltages, whether balanced or not, of the generator should equal zero i.e they form a closed triangle. If it is not so with your readings i.e a closed triangle is not possible even approximately, it means the phase angle between phase windings are not correct i e the winding issue.

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Originally Posted by ATSman
Gentlemen
and comment back
a floating neut will not make v l-n 3 x v l-l
either he made a posting error and v l-l is 600 and v l-n 150-300 or there are major connection issues

the ONLY way for this to occur
v l-n for a, b, c ~ 600/0, +15-20, -15-20 deg

this will give a l-l using a ph ~ +/- 17 deg
v a + (- v b) = vab
va = 600 + 0j
vb = -(575 + 175j)
vab = 25 + 175j = 175/82
similarly vac ~ 175/-82

vbc
0 + 350j ~ 350/90
Last edited by Ingenieur; 05-05-18 at 01:06 PM.

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On occasion I get the feeling that OPs have an moment and donâ€™t bother coming back. I have them often enough.

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Originally Posted by Sahib
The vector sum of line or phase voltages, whether balanced or not, of the generator should equal zero i.e they form a closed triangle. If it is not so with your readings i.e a closed triangle is not possible even approximately, it means the phase angle between phase windings are not correct i e the winding issue.
If vector sum of line or phase voltage readings of the generator by OP does not equal zero ie they do not form a closed triangle even approximately, it implies erroneous readings or a break in generator windings.

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+(vab = 25 + 175j) or 175/82
-(vac = 25 - 175j) or 175/-82
-(vbc = 0 + 350j) or 350/90
= 0 + 0j

something does not compute
one machine in reverse rotation
messed up connections
etc or some combination

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I don't understand, if the neutral is kept floating, then aren't any line to neutral voltage readings meaningless?

If the voltage readings are true, I can't really wrap my head around it either except to speculate that a neutral and a phase are reversed or one generator has its windings in series rather than parallel. I would compare connections to the other six generators that are working fine, try to rule out any obvious errors

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