alsafaj
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- Dubai, UAE
Negative sequence voltage calculation
- Thread starter alsafaj
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is that a fault or switching transient?
ground fault?
they look like pos seq voltages
under no fault the neg seq will be ~ 0
graph is hard to read
my guess
do you understand symmetrical components?
basically if you have a phase fault (vs ground fault) you will have neg seq current flow
if your normal phase seq is abc, you will have current with seq acb
if this results in a voltage > than 19.05 your relay trips
looks like system v is 132 kv?
ground fault?
they look like pos seq voltages
under no fault the neg seq will be ~ 0
graph is hard to read
my guess
do you understand symmetrical components?
basically if you have a phase fault (vs ground fault) you will have neg seq current flow
if your normal phase seq is abc, you will have current with seq acb
if this results in a voltage > than 19.05 your relay trips
looks like system v is 132 kv?
junkhound
Senior Member
- Location
- Renton, WA
- Occupation
- EE, power electronics specialty
Paper or electronic strip chart?
You need to get an accurate phase differential to get negative anzero sequence values. Best to do with electronic cursor, a paper graph if that is what is shown takes some good eyeballing with sharp pencil and scale.
positive and negative sequence are exactly 120 deg apart, vecotor sums (plus zero sequence) = what you actually have. My old eyes see very little phase separation imbalance in the chart shown.
You need to get an accurate phase differential to get negative anzero sequence values. Best to do with electronic cursor, a paper graph if that is what is shown takes some good eyeballing with sharp pencil and scale.
positive and negative sequence are exactly 120 deg apart, vecotor sums (plus zero sequence) = what you actually have. My old eyes see very little phase separation imbalance in the chart shown.
I'm with the others. It doesn't look like negative sequence.
I think that is a model output
can't read the scales though
looks like a phase fault is initiated...first discontinuity
resulting in a neg seq v
which opens the cb resulting in a transient over-voltage
when transformed from the seq to the ph domain the neg seq (or zero seq) components can add (or subtract) to the ph domain magnitude
so even though we are looking at the ph seq magnitude the neg seq can increase it
the phase is basically the sum of the pos, neg and 0 seq after a ph shift transform matrix is applied
(the inverse of the one used to extract the 3 seq components from the ph domain)
the grads look like 20k
and the fault looks like 2.4 grads or 48k
this imo is the neg seq contribution
ref to rms and gnd = 48000/(sqrt 2 x sqrt3) ~ 19.5 kv
so even though we are looking at the ph seq magnitude the neg seq can increase it
the phase is basically the sum of the pos, neg and 0 seq after a ph shift transform matrix is applied
(the inverse of the one used to extract the 3 seq components from the ph domain)
the grads look like 20k
and the fault looks like 2.4 grads or 48k
this imo is the neg seq contribution
ref to rms and gnd = 48000/(sqrt 2 x sqrt3) ~ 19.5 kv
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alsafaj
Member
- Location
- Dubai, UAE
I am going to share better resolution pics..
This is a disturbance recorder system -- monitoring the analog and binary inputs of a 132 kV line. See that a negative sequence voltage trigger is set to 19.05 kV --
Looking at the graphs -- the voltage sequence and current sequence are maintained except for phase B-N the magnitude has changed.
See more:
Phil Corso
Senior Member
- Location
- Boca Raton, Fl, USA
Alsafa...
For voltage values on chart, calculated Neg-Seq is 23.3 kV, which is above the trip set-point! What are you questioning?
Regards, Phil Corso
For voltage values on chart, calculated Neg-Seq is 23.3 kV, which is above the trip set-point! What are you questioning?
Regards, Phil Corso
I come up with +/- 20 kv
regardless
I think he wanted to understand
where did the trip of 19.05 come from
and how a neg seq component impacts the measured pos seq
alsafaj
Member
- Location
- Dubai, UAE
Pre-fault is set to 100ms and fault is 2 secs
Vb-n is 107.7 kV -- spike is ~ 156.2
Delta is ~ 48.70 kV
alsafaj
Member
- Location
- Dubai, UAE
Yes, you are right I wanted to understand exactly this
156.2 - 107.7 ~ 48.5
normalized to rms and ph-n ~ 19.8 > 19.05 so tripped
I hope we answered your questions
these are good primers on sym comp
https://cdn.selinc.com/assets/Liter...etrical-Pt1_AR_20130422.pdf?v=20170713-070622
https://www.gegridsolutions.com/smartgrid/Dec07/7-symmetrical.pdf
look at equation set 4 in first link
you can see ph a (v or i) = sum of seq comp = 0 seq + pos seq + neg seq
what this means is when you have a ph-ph fault neg seq components are created
these increase the summed measured value
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alsafaj
Member
- Location
- Dubai, UAE
Ah, got it. I understand now. Thank you!
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