Reclosing on Covered Wire

[Mbrooke]

Is reclosing necessary on covered wire distribution circuits? I have a few scenarios where overhead feeders will temporarily be protected by SM fuses.

 

[cuky2000]

Please clarify the meaning of "covered wire".

 

[davidbeach]

If the covered wire (tree wire or Hendrix) is the only possible exposure you might get away with it. But if you try "fuse saving" you absolutely must reclose. If there's any non-covered wire on the line side of the cutouts there will be a limb or a squirrel get on that exposed conductor. The customers will appreciate a reclose or two to try to let the problem fall clear.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[Mbrooke]

@Cuky200-

This:

https://www.mysouthwire.com/medias/...090186782/Multi-Layer-15kV-35kV-Tree-Wire.pdf

And this:

https://www.mysouthwire.com/medias/.../Multi-Layer-15kV-46kV-CAMV-Spacer-Cable-.pdf

Its good stuff

I avoid calling it insulation because it 1) still shocks badly 2) it tracks through. Always treat it as live, always.

@David: You know what I want to hear Good to know this.

Not my pic, but to give you an idea of why I ask:

https://www.reddit.com/r/SubstationTechnician/comments/i84lp1/mobile_substation_install/

SMD and SM fuses make for a good reliable alternative.

 

[davidbeach]

Mobiles have low-side breakers and can do reclosing.

I’ll see your silver lining and raise you two black clouds. - Protection Operations

 

[Mbrooke]

Not the mobile pictured above, take a look again

 

[Oblsss]

Mrbrooke,

In addition to what @David mentioned above, keep in mind that the occurrence of an electric arc in distribution circuits with covered conductors is more dangerous comparing to one in distribution circuits with bare conductors and usually results to a burndown of the conductor.

Link

The electric arc can result from a number of faults:

1. limb or a squirrel mentioned above
2. prolonged contact with an earthed object
3. exposed metallic parts in the circuit, i.e. terminations
3. lighting overvoltage etc.

When an electric arc ignites, it burns a small hole in the covering and keeps burning until the conductor is damaged or burned through.
SM fuses are too slow to protect you from this!


Regards,

George

 

[Mbrooke]

Thanks.

But if SM fuses are to slow, wouldn't the same hold true for 50/51 elements in relays?

 

[Oblsss]

Where I am from, a small country in Europe, the DNO uses a spark gap(in parallel with a MOV) every third pole in radial circuits …
In ring circuits it is even more complicated/expensive …

Regards,

George

 

[cranky108]

Covered wire does not extend to switches, arresters, and other pole top equipment, which is where most animal contacts happen. So why do you have covered wire? What concern was this installed to fix?

 

[Mbrooke]

Covered wire can be extend to recloser, arrestor and switch bushings, and those bushings can be equipped with covered boots.

The goal of covered wire is to prevent blinks (and even outages) from tree contact and high wind. Covered wire can also be implemented between fuses and transformer bushings to reduce animal related outages:

https://www.mysouthwire.com/medias/.../h54/8854090350622/Transformer-Riser-Wire.pdf

I know there are some EEs/Lineman/POCO individuals who will speak strongly against covered wire because it often falls without tripping devices, however at the same time, it greatly increases service continuity in treed areas. Not so much when wires come down, but when wind pushes tree limbs into wires.

 

[cranky108]

" from tree contact and high wind", maybe so, but I have seen line-people invent solutions for problems that have nothing to do with the real problem.

That said, if the real problem is not trees, reclosing may be useful, or if the covering is not complete.

 

[Mbrooke]

So your saying spacer cable and tree wire is just a gimmick?

 

[cranky108]

Spacer cable or tree wire, is a possible solution for a specific problem. But it can be misapplied to other problems, or not applied correctly, or completly.

As an engineer, you need to look at the problems now and when the cable was installed, and make a decision on what to do next.

 

[Mbrooke]

Possible? It is thee solution for some POCOs and municipals. Service continuity sky rockets and tree trimming is actually reduced.

As long as the dielectric constants match (you don't have spacer wire on porcelain insulators), messenger torqued correctly, ect you're good.

But it can be misapplied to other problems, or not applied correctly, or completly.

I think your talking about distribution network automation.

 

[Palletjack]

. Service continuity sky rockets and tree trimming is actually reduced.

As long as the dielectric constants match (you don't have spacer wire on porcelain insulators), messenger torqued correctly, ect you're good.

So if you had the opportunity you would sacrifice public safety with wire on a system that would possibly stay energized laying on the ground just for service continuity and saving trees?

Tell me about your experience with this..

 

[Mbrooke]

Well, you're painting over a dozen large utilities with a very broad brush when you make that statement. Utilities who are now using tree wire and spacer cable almost exclusively.

As far as I'm concerned a down wire should be avoided bare or not. Being bare doesn't guarantee a device will trip as evidenced by countless public filmed videos.

Sure a covered conductor is less likely to trip when down (in theory), but less likely to set a resting tree branch ablaze before crews disconnect power and remove it. Weigh that in addition to how essential power is for buildings where people depend on it.

What appears to be bare wire, on a swing set, arcing to the fence:

https://www.youtube.com/watch?v=28Xq3JulV1o&feature=youtu.be&t=92

 

[Oblsss]

Please do not forget that large fires that result in the death of people and animals as well as long-term natural disasters have started from power distribution systems.

Having pointed this, a bare conductor in contact with the concrete floor of a road has low chances of tripping the breaker.
On the other hand, a bare conductor in contact with earth in a rural area has high chances of setting up a fire!

 

[cranky108]

So how do you propose to fix the issue of a bare conductor in contact with earth in a rural area?

If utilities are to be required to pay for the fire damage, perhaps utilities should rase rate now to pay for future fire damage, that maybe greater for poorly maintained forest land.

Then again, people are required to call ahead before digging, but they don't.

 

[Oblsss]

Hello cranky108,

[highlight #FCE94F]If utilities are to be required to pay for the fire damage, perhaps utilities should rase rate now to pay for future fire damage[/highlight]

As I mentioned above, I come from a small country in Europe and penalties for fire damage were the main reason behind the introduction of covered conductors in the distribution system.
Vegetation management programs works in parallel with the investment for the replacement of bare conductors.

Nevertheless, the issue of a bare conductor in contact with earth in a rural area cannot be solved only by replacing all bare conductors with covered wires.
It probably needs a sophisticated protection system that can separate an open circuit condition from a low load condition, i.e. high-impedance fault detection, which poses other problems depending on the nature of the circuit and the position of the breaker ...

George