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Reclosing on Covered Wire
- Thread starter Mbrooke
- Start date
For a non-POCO guy could someone define "reclosing" as the original question is not making sense to me.
Don't you always have to reclose? How do you ever re-energize if you don't reclose?
How can you look at a trailer covered with electrical apparatus and say "it can't reclose"?
Keith Cress
kcress -
Don't you always have to reclose? How do you ever re-energize if you don't reclose?
How can you look at a trailer covered with electrical apparatus and say "it can't reclose"?
Keith Cress
kcress -
- Thread starter
- #23
@Oblss: Question- how are substation transformers grounded in your country? What is the primary connection of pole transformers? Do you have 3 or 4 wires on your MV circuit? What voltage do you use?
I've always known that in the EU transformers are almost always delta primary which lets you set ground pick to a very low value.
@Itsmoked: Others can explain it better than I can, but by reclose I mean reclose automatically. (ANSI 79) Meaning if the feeder trips out automatically on over-current it will close back in automatically after a few seconds. If the fault is still there the circuit will trip back out automatically. In my case the feeder won't close back in after the very first trip.
This is different from re-energizing a feeder manually after circuit repair or inspection.
I've always known that in the EU transformers are almost always delta primary which lets you set ground pick to a very low value.
@Itsmoked: Others can explain it better than I can, but by reclose I mean reclose automatically. (ANSI 79) Meaning if the feeder trips out automatically on over-current it will close back in automatically after a few seconds. If the fault is still there the circuit will trip back out automatically. In my case the feeder won't close back in after the very first trip.
This is different from re-energizing a feeder manually after circuit repair or inspection.
- Thread starter
- #25
@Mbrooke
A typical distribution transformer would be DYn, 20/0.4 kV with the LV side resistance grounded, thus the MV circuit is 3 wires.
As for the ground pick, I think that high impedance faults as the one described above are detected by negative sequence current measurements more accurately ...
If you have come across different approaches I would like to hear them, my scope of work was mainly in choosing the type of covered wire and related accessories but I am interested in a general approach.
George
A typical distribution transformer would be DYn, 20/0.4 kV with the LV side resistance grounded, thus the MV circuit is 3 wires.
As for the ground pick, I think that high impedance faults as the one described above are detected by negative sequence current measurements more accurately ...
If you have come across different approaches I would like to hear them, my scope of work was mainly in choosing the type of covered wire and related accessories but I am interested in a general approach.
George
- Thread starter
- #27
Most of our distribution is multi-grounded, but in some areas, that is not very good, you know sand, or rock. But we have had problems balancing distribution circuits, so we do use a ground setting higher than 2/3. Actually we have seen large load changes from season to season, and around holidays. As a dual peaking utility, it is hard to predict between compressor AC and electric heat, and holiday lights to the max.
We also have a few old delta circuits, where the ground fault currents calculate to about 5 amps, which is hard to detect and it has started fires.
My old company had tried covered conductors years before I worked there. They looked bad as the insulation was pealing off, or hanging off the wire. That's my thoughts on it.
But now the company I work for only has 30 foot right-of-ways, so they can not trim outside of that, and we still get trees bending so much in the wind to come into contact. The customers want us to underground the old lines, but don't want us to dig up the tree roots, and don't like the green boxes.
Though we have more problems with animal contacts, where people feed the things. Tree wire does not fix this, and animal guards only work so-so.
A comment on negative sequence, most three phase solar inverters do not create negative sequence into a fault, so you can't depend on them for that, or those for directional support.
We also have a few old delta circuits, where the ground fault currents calculate to about 5 amps, which is hard to detect and it has started fires.
My old company had tried covered conductors years before I worked there. They looked bad as the insulation was pealing off, or hanging off the wire. That's my thoughts on it.
But now the company I work for only has 30 foot right-of-ways, so they can not trim outside of that, and we still get trees bending so much in the wind to come into contact. The customers want us to underground the old lines, but don't want us to dig up the tree roots, and don't like the green boxes.
Though we have more problems with animal contacts, where people feed the things. Tree wire does not fix this, and animal guards only work so-so.
A comment on negative sequence, most three phase solar inverters do not create negative sequence into a fault, so you can't depend on them for that, or those for directional support.
- Thread starter
- #29
My present company does not have any covered wire that I know of.
I suppose the animal guards are secured, as we seem to see pictures in the outage meetings, and they appear to be.
But animal guards don't work in underground boxes. Snakes can find openings.
I suppose the animal guards are secured, as we seem to see pictures in the outage meetings, and they appear to be.
But animal guards don't work in underground boxes. Snakes can find openings.
- Thread starter
- #31
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