Birds Don't Like Wires Over 21 kV 3

[JohnMcNutt]

Here is a question that has bugged me for a long time but I never bothered to ask:

Does anyone know why birds do not perch on wires > 21 kV?

There are no 35 kV in this area so I don't know what they think of those.

I know I have never seen them perched on 60 kV or greater unless they are deenergized.

It must not kill them or else you would see dead birds for miles.

Do they not like electric field close to the wires?

Has this ever been studied?

 

[itsmoked]

I suspect the possibility of corona disturbs them.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Mbrooke]

My best educated guess would be:

1. Heat (higher loading on these circuits)

2. Higher electric field

3. Larger conductor size


Of course I could be very wrong since I know nothing about birds.

 

[Skogsgurra]

Whenever you are getting close to a naked wire (from a helicopter, for instance) there is a little (or quite nasty) spark before you establish a well conducting path with the wire.

Once on the wire, you do not feel anything. It's the spark that the birds don't like. I guess that they can sit on an de-energized wire and that they will continue sitting there when the wire gets energized again.

But they will not love the tickling when they leave the wire.


Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Skogsgurra]

Wasn't difficult to find a clip on this. Not my kind of work.

http://www.bing.com/videos/search?q...3CFBE65D532926D0EE163CFBE65D53292&FORM=VRDGAR

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[bacon4life]

In addition to the large spark seen in the video when attaching to or detaching from the wire, there is a steady state AC current flowing that charges and discharges the line worker each cycle. The worker is wearing a metal suit to equalize the electric field around their body so that the steady state current flows in the suit and not the worker's skin.

Although some wires do operate at uncomfortably high temperatures, many are also operated close to ambient. For many of our transmission lines, the lines will be warmer while de-energized on a still sunny day, than carrying typical power flows on a windy (> 2 m/s windspeed) cloudy day.

 

[Mbrooke]

How many Ma is that spark?

Do you get a spark because the bird is one plate of a capacitor and the wire is another plate and when the two get close they discharge?

 

[Skogsgurra]

Yes, the capacitor analogy is correct. But there are three "plates" in the capacitor; the wire, the bird and the universe (or ground).

The arrangement is actually a capacitive voltage divider, like a capacitive PT, and current depends on equivalent capacitance, voltages involved and the Paschen's and other guy's laws. For a bird, it cannot be a lot of current. But nasty enough.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[jraef]

Probably every bird has done it once though. We tend to think of them as stupid, but they are far from it. It's not likely 21kV though, behind my house we have some 25kV lines and above them, a set of 230kV lines. The 25kV lines are crowded with birds, especially during migration times, and are a favorite for hawks and eagles looking for rodents in the creek below. But the 230kV line are always clear. I once observed a young eagle go up from the 25kV line to get a higher perch and start to land on the 230kV, but immediately fly off, I think before he even touched it. They do perch on the cross arms though. So birds definitely use trial and error learning.

A pair of Turtle Doves has discovered, likely through trial and error, that the pine tree over my driveway is close enough to get some heat from the house, but dense enough to protect them from raptors. So they roost in the exact same spot every night and as you might imagine, my car ends up being their toilet. I tried a lot of things to discourage them from that roosting site, shiny balloons, mylar ribbons, a fake owl on the chimney, all with limited or no success. So for the past week I have been going out after dark, rain or shine, with my head lamp and a "wrist rocket" sling shot to fire a group of tiny pebbles into the tree where they are, just enough to disturb them. The first night they came back after an hour, the third night it was 3 or 4 hours, last night they finally did not come back. They learned...


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[transmissiontowers]

I'm a structural guy and design T-Line poles and towers. Our EE's say the bird's feathers are affected by the corona around the HV lines. We don't have any HVDC and I wonder if the same thing happens there. When transmitting a lot of amps, the conductors get very hot. We run them as high as 300°C in an emergency and up to 250°C in normal operations which is hot enough to boil water. I suspect the high temps burn the bird's feet.

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[waross]

Wow! 250 degrees C! I gotta throw the BS flag on that one.
The rain does not boil off of transmission lines.
A line of any length at that temp would have losses greater than the load.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Skogsgurra]

Probably was Farenheit some time long ago. That would still be quite hot. But not impossible. What does 300 C do to elongation and tensile strength? Nothing good - that's for sure. BTW, never saw design rules allowing such high temperatures. Never, ever.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[transmissiontowers]

You have to use high temp conductor to run it that high and I can assure you 250°C is the rating. You use ACSS (Aluminum Conductor Steel Supported) where the 270 ksi or 285 ksi steel core wire takes the tensile stress and the outer aluminum strands are totally annealed. On normal ACSR the aluminum is alloyed and takes the tension load. If you run ACSR too hot for too long, it will anneal the aluminum and you get run away creep and the aluminum fails then the steel core strands can't take the tension and it can fail.

Way back, they used to only run the ACSR 75°C normal rating and 90°C emergency. Later they used 90°C normal and 120°C emergency. They started to develop the high temperature wire to push more power down the lines. If the lines are lightly loaded, electrically, they are not too much above ambient and in the very cold weather, they will ice over and start galloping because of the shape of the ice. During the summer when everyone is running the air conditioner, the wire temperature goes up and the wire can sag an extra 20 feet from the unloaded position on an average 800 foot span.

Below is the output from a Sag-Tension program for a 795 MCM ACSR conductor on an 800 foot span in a 120 mph hurricane. When the wire is first strung, the sag is 13.50 feet at 60°F. After it creeps and gets loaded up, the sag goes to 25.36 feet at a max emergency operating temp of 120°C. The wire tension goes up to 12,907 pounds in a 120 mph wind from the initial stringing tension of 6501 pounds. The conductor has 26 aluminum strands over 7 steel core strands and is 1.108 inches diameter.

[pre] WC Weather Case Condition Allowable Actual Allowable Actual Allowable Actual % of OK
No. Description % of % of Tension Tension Catenary Catenary Allowable or
Ultimate Ultimate (lbs) (lbs) (ft) (ft) Capacity NG.
-----------------------------------------------------------------------------------------------------------------
6 60F Initial RS 33.0 20.6 6501.2 5929.1 62.5 OK
6 60F Creep RS 18.0 18.0 5667.1 5164.7 99.9 OK *
11 Hurricane Initial RS 50.0 41.0 12909.3 3664.5 82.0 OK
12 NESC LIGHT Initial RS 50.0 26.3 8272.8 5796.4 52.5 OK


Ruling Span Sag Tension Report

---Weather Case--- | --Cable Load-- | -----R.S. Initial Cond.---- | ------R.S. Final Cond.----- |
| | | --------After Creep-------- |
# Description | Hor. Vert Res. | Max. Hori. Max R.S. | Max. Hori. Max R.S. |
| -----Load----- | Tens. Tens. Ten C Sag | Tens. Tens. Ten C Sag |
| ---(lbs/ft)--- | (lbs) (lbs) %UL (ft) (ft) | (lbs) (lbs) %UL (ft) (ft) |
--------------------------------------------------------------------------------------------------
1 15F 0.00 1.09 1.09 7690 7678 24 7018 11.40 6828 6814 22 6229 12.85
2 25F 0.00 1.09 1.09 7399 7386 23 6752 11.85 6533 6518 21 5958 13.43
3 30F 0.00 1.09 1.09 7265 7252 23 6629 12.07 6391 6376 20 5828 13.73
4 40F 0.00 1.09 1.09 6996 6982 22 6382 12.54 6131 6115 19 5590 14.32
5 50F 0.00 1.09 1.09 6741 6727 21 6149 13.02 5890 5874 19 5369 14.91
6 60F 0.00 1.09 1.09 6501 6486 21 5929 13.50 5667 5650 18 5165 15.50
7 70F 0.00 1.09 1.09 6277 6262 20 5724 13.98 5464 5446 17 4978 16.08
8 80F 0.00 1.09 1.09 6060 6044 19 5525 14.49 5275 5257 17 4805 16.66
9 90F 0.00 1.09 1.09 5859 5842 19 5340 14.99 5101 5082 16 4646 17.23
10 100F 0.00 1.09 1.09 5671 5654 18 5169 15.49 4938 4919 16 4496 17.80
11 Hurricane 3.33 1.09 3.50 12909 12833 41 3664 21.85 12907 12830 41 3664 21.86
12 NESC LIGHT 0.83 1.09 1.42 8273 8253 26 5796 13.81 7579 7558 24 5308 15.08
15 Rule 250 D 0.40 2.09 2.13 10580 10546 34 4945 16.19 10279 10243 33 4803 16.67
16 75C(167) 0.00 1.09 1.09 4668 4648 15 4248 18.84 4114 4090 13 3739 21.42
17 90C(194) 0.00 1.09 1.09 4368 4346 14 3973 20.15 3871 3846 12 3516 22.78
20 120C(248) 0.00 1.09 1.09 3887 3863 12 3531 22.68 3483 3456 11 3159 25.36
23 200C(392) 0.00 1.09 1.09 3081 3050 10 2788 28.75 3065 3034 10 2773 28.90
24 250C(482) 0.00 1.09 1.09 2880 2846 9 2602 30.81 2868 2834 9 2591 30.94
25 BLOWOUT 60 0.55 1.09 1.23 6938 6921 22 5644 14.18 6152 6132 20 5001 16.01
26 FIRST CRACK CHK 0.55 1.09 1.23 6938 6921 22 5644 14.18 6152 6132 20 5001 16.01
27 Max Temp 0.00 1.09 1.09 2880 2846 9 2602 30.81 2868 2834 9 2591 30.94
28 Min Temp 0.00 1.09 1.09 8143 8131 26 7432 10.77 7323 7309 23 6681 11.98
29 Rule 230B1 0.83 1.09 1.42 8273 8253 26 5796 13.81 7579 7558 24 5308 15.08
[/pre]

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[stevenal]

Sounds like fault current temperatures. The conductors can recover if the exposure is brief. The Aluminum Conductor Handbook charts emergency loading temperature versus strength from 100 C to 150 C. Still hot enough to boil water and cook a bird.

 

[waross]

4IK25GN-S5T6

That makes a lot of sense stevenal.
I have never seen it but has anyone else seen rain turning to steam or water vapor on transmission lines??

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[transmissiontowers]

The rated ampacity of Drake 795 ACSR is 907 amps per wire and we run a 2 wire bundle at 138kV and 345kV. Some equipment in our substations is rated for 5000 amps. IIRC, the fault current is 63,000 amps for 138kV and 80,000 amps at 345kV but it should only last a few cycles before it trips a breaker.

http://www.southwire.com/ProductCatalog/proddetail.jsp?htmlpreview=true&token=16&desc=ACSR

500kV switch opening.

https://www.youtube.com/watch?v=PXiOQCRiSp0

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[Mbrooke]

I have been called "A storehouse of worthless information" many times.

Uhhh, you might want to reconsider that. Simply no- in fact the opposite. For a structural guy this rivals what many long standing EEs post here- and they know their stuff. Great info!


As for not seeing steam- its a guess- but its possible that since water has a much higher thermal absorption capacity that it cools the conductor down significantly over 2ft/wind or still air temps.

 

[transmissiontowers]

Thanks for the kind words. I've picked up a little Electrical knowledge over the past 43 years of designing structures for Substations. The fault current gives me a Short Circuit Force on the buswork that I use to design the structure with other wind loads for extreme conditions. I know enough not to raise my hand too far inside a substation and to shuffle my feet if I hear any arcing (too much step potential between one foot and the other if you run).

AFA, the rain on hot conductor, I'm only guessing that it flashes to steam as the drops hit if it is indeed at or near max operating load. On foggy days you can hear the crackle around the wires which I assume are the tiny water drops flashing to steam. I'll have to ask the EE over the cubicle wall.

_____________________________________
I have been called "A storehouse of worthless information" many times.

 

[Compositepro]

"I know enough not to raise my hand too far inside a substation and to shuffle my feet if I hear any arcing (too much step potential between one foot and the other if you run)."

If you are actually "running", only one foot will be in contact with the ground at any time. However, a good thing to keep in mind.

 

[Skogsgurra]

The crackling sound is corona discharges aka PD and has nothing with water vapour to do.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.