High voltage transmission 4

[Herb765]

Will someone please explain what are the small coned shape devices on high voltage transmission lines? They are located near the insulators on the lines. I have seen them on 138 KV transmission lines and less.
Sometimes they are every tower and sometimes not, maybe every other tower.

Thanks,

Herb765

 

[davidbeach]

Do you have any pictures?

 

[HamburgerHelper]

I think you might be looking at anti-nesters for birds.

 

[itsmoked]

No! Those are to absorb solar wind and couple it into the power grid..

HamburgerHelper; Kidding aside, thanks for the pictures. Those are interesting bird-cones. I haven't seen either of those styles before.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Mbrooke]

You mean corona rings?

https://upload.wikimedia.org/wikipe...tors.png/220px-Corona_rings_on_insulators.png

Edit, guess not lol. Do you have any pics?

 

[magoo2]

No, you wouldn't find corona rings on 138 kV lines.

 

[waross]

If the devices are hanging from the conductors they are probably vibration dampers. If the devices are mounted on the cross-arms as in the picture they are probably anti-nesting devices.

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

 

[dpc]

Squirrel/bird guards.

 

[Mbrooke]

@magoo, never state anything as being an undeniable absolute. There are plenty of older 138 and 115kv lines with corona rings having seen them first hand. Here is one example looking at the lines in the background:

http://www.ipernity.com/doc/321461/42869048/sizes/2048

This is indeed 138kv

http://www.ipernity.com/doc/321461/42869048

 

[waross]

Here are some more pictures of corona rings.
Link

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

 

[HamburgerHelper]

Mbrooke,

I guess someone working for the utility had a friend who sold corona rings.

 

[Mbrooke]

Maybe, but to be honest I've seen many early transmission lines (pre 40s) with corona rings in addition to some substation equipment having it as well. Best I can gather is that in that era be it belief or necessity the tendency was there to use corona rings at lower voltages. My understanding (though limited) is that in some parts of the world its still done to this day on 110 and 132kv lines.

 

[waross]

Here are vibration dampers:
Link

Some of the illustrations for Corona Rings show rings on both ends of insulator strings. There is no corona whatever at the grounded end of the insulator. Those are grading Rings.
From Wiki:
Grading rings
A very similar related device, called a grading ring is also used on high voltage equipment. Grading rings are similar to corona rings, but they encircle insulators rather than conductors. Although they may also serve to suppress corona, their main purpose is to reduce the potential gradient along the insulator, preventing premature electrical breakdown.

The potential gradient (electric field) across an insulator is not uniform, but is highest at the end next to the high voltage electrode. If subjected to a high enough voltage, the insulator will break down and become conductive at that end first. Once a section of insulator at the end has electrically broken down and become conductive, the full voltage is applied across the remaining length, so the breakdown will quickly progress from the high voltage end to the other, and a flashover arc will start. Therefore, insulators can stand significantly higher voltages if the potential gradient at the high voltage end is reduced.

The grading ring surrounds the end of the insulator next to the high voltage conductor. It reduces the gradient at the end, resulting in a more even voltage gradient along the insulator, allowing a shorter, cheaper insulator to be used for a given voltage. Grading rings also reduce aging and deterioration of the insulator that can occur at the HV end due to the high electric field there.


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

 

[Mbrooke]

Not disagreeing, but then what is the function of a corona ring? The rings pictured in my posts do not encircle the insulators themselves. I always thought reducing the electric field around an insulator was either the intended or secondary effect of a corona ring in addition to reducing corona discharge. In fact the wiki link for corona rings shows rings at each end of the insulator:

https://en.wikipedia.org/wiki/Corona_ring#/media/File:Corona_rings_on_insulators.png

https://en.wikipedia.org/wiki/Corona_ring

 

[waross]

At higher voltages, electrons will be forced off of conductors. On a long high voltage line, the cumulative effect of these losses may become a significant revenue loss. That is, enough revenue loss to justify the cost of mitigation.
The loss of electrons or "Corona" loss is more severe from sharp points. A smooth "Corona Ring" creates a larger radius surface to reduce Corona. This is related to the Faraday Cage effect.
Typically corona Rings will be placed on each side of the hardware connecting the conductors or conductor bundles to the insulator string.
This effectively shields the sharp corners and edges of the bolts and other hardware used in the fastening.

Guard Rings may, in some cases, be similar in appearance and construction to Corona Rings but the function is different.
One function of Guard Rings is to avoid damage to insulators strings caused by lightning induced flashovers.
The flash over will tend to be from ring to ring rather than directly across the surface of the insulator string.
Grading Rings may be employed at lower voltages than Corona Rings as lightning strikes do not respect the operational voltage of the targets.
Or, if you prefer, from the Wiki link:

Grading rings
Grading rings along linear accelerator beam tube at University of Pennsylvania in 1940.

A very similar related device, called a grading ring is also used on high voltage equipment. Grading rings are similar to corona rings, but they encircle insulators rather than conductors

Looking at the title of the Wiki article and then jumping to the illustrations is very confusing. Most of the illustrations are of Grading Rings rather than Corona Rings.
But this thread is questioning the purpose of unknown devices attached to transmission lines, so it's all good.

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

 

[GroovyGuy]

Correct me if I am wrong, but are these not spikes to prevent birds from roosting near HV lines? I know if I were a bird, I would look for somewhere else to perch.

"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)

 

[waross]

Hi GG
That is probably the correct explanation for the original post.
However the discussion somehow expanded to include other devices that may be attached to or near high voltage insulators.
I note that the OP has not been back.

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

 

[Mbrooke]

Waross, thank you The Wiki pics threw me off as they show one labelled as the other and visa-versa. But, in the pic of the 138kv substation, do those look like grading rings or Corona rings? Im genuinely confused atm.

 

[waross]

A quick discussion of one factor affecting corona before answering your question.
Corona is a result of a steep electrical field gradients.
Corona is more pronounced from sharp points or edges which tend to produce higher field gradients than flat surfaces.
Corona may be reduced by reducing the effective radius of a surface.
A rectangular shape may have a very small radius corner, but the fields from each surface will interact at the corners so as to increase the effective radius of the corner.
The outside radius of a two conductor bundle will have a greater effective radius than one of the conductors by itself.
A four conductor bundle will have a still greater effective radius than the two conductor bundle or a single conductor.
Corona losses along the length of a transmission line may be reduced by using conductors of greater diameter and further reduced by using bundles rather than single conductors.
Another source of corona is the sharp edges (Small effective radius) of the corners of hardware and bolts, nuts and cotter pins.
Corona rings are generally placed on each side of the conductor ends of the insulators. The rings are made of fairly large diameter tubing And are in the shape of ovals or rectangles with semi-circular ends. The voltage field gradients develop outside the profile of the rings eliminating corona discharge from sharp edges within the space encircled by the rings.

Now with that background, let's consider the grading rings. Although the purpose of the grading ring is to reduce non-linear stresses in the insulator string, the grading ring itself should not cause corona.
To that end, the grading ring on the conductor end of the insulator should be constructed much in the same manner as a corona ring.
A guard ring would probably function as a guard ring if it were to be constructed of a ring of 1/8" x 2" flat strip bent in a circle.
Such a construction would function as a guard ring but would possibly introduce unwanted corona discharges.
How to tell the difference?
Corona Rings will be fastened in pairs at each side of the lower end of the insulator string to form a Faraday Cage around the fastening hardware.
Guard Rings will be installed around each end of the insulator. The guard ring on the lower insulator will be constructed in such a way so as to not introduce corona discharge.
With new designs the connecting hardware may be constructed with smooth surfaces and be encircled by a four conductor bundle, so corona rings may not be needed. In the old days of single conductor lines and rough and ready fastening hardware with lots of sharp edges and exposed threads, corona rings were needed at much lower voltages than today.

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

 

[davidbeach]

Corona may be reduced by reducingincreasing the effective radius of a surface.

Typo.