Electrical Engineering - HV transmission lines

Author

HV transmission lines - UK practice.

furles@mail.croydon.ac.uk

2007-05-20, 1:25 pm

I've recently noticed something on overhead HV transmission lines that
I can't think of a purpose for. Close to each tower, there is
something hanging down below each conductor, including the Earth
conductor at the top of the tower. Where the conductors consist of
bundles of cables, each one will have these things fitted. They are
shaped like a letter 'L' turned on its side, with the short part
vertical and attached to the cable, and the horizontal longer part
running parallel to the cable, and below it by a few cable diameters.
the horizontal part looks like a foot or two long, but it's difficult
to judge from ground level, some distance away, These things are
fitted in pairs, pointing in opposite directions, and are fitted a few
metres from where the conductors are attached to the insulator strings
at each tower. There is usually one pair on each conductor on each
side of each tower, but occasionally a second or even third pair can
be found, at roughly equal spacings. They look almost like small
radio dipoles, but that wouldn't make any sense. Does anybody know
what they are?

Charles Perry

2007-05-20, 1:25 pm

<furles@mail.croydon.ac.uk> wrote in message
news:1179682647.387407.160690@b40g2000prd.googlegroups.com...
> I've recently noticed something on overhead HV transmission lines that
> I can't think of a purpose for. Close to each tower, there is
> something hanging down below each conductor, including the Earth
> conductor at the top of the tower. Where the conductors consist of
> bundles of cables, each one will have these things fitted. They are
> shaped like a letter 'L' turned on its side, with the short part
> vertical and attached to the cable, and the horizontal longer part
> running parallel to the cable, and below it by a few cable diameters.
> the horizontal part looks like a foot or two long, but it's difficult
> to judge from ground level, some distance away, These things are
> fitted in pairs, pointing in opposite directions, and are fitted a few
> metres from where the conductors are attached to the insulator strings
> at each tower. There is usually one pair on each conductor on each
> side of each tower, but occasionally a second or even third pair can
> be found, at roughly equal spacings. They look almost like small
> radio dipoles, but that wouldn't make any sense. Does anybody know
> what they are?
>

Sound like vibration dampers. Helps to keep the conductors from galloping
when the wind blows.

Charles Perry P.E.

Andrew Gabriel

2007-05-20, 5:25 pm

In article <1179682647.387407.160690@b40g2000prd.googlegroups.com>,
furles@mail.croydon.ac.uk writes:
> I've recently noticed something on overhead HV transmission lines that
> I can't think of a purpose for. Close to each tower, there is
> something hanging down below each conductor, including the Earth
> conductor at the top of the tower. Where the conductors consist of
> bundles of cables, each one will have these things fitted. They are
> shaped like a letter 'L' turned on its side, with the short part
> vertical and attached to the cable, and the horizontal longer part
> running parallel to the cable, and below it by a few cable diameters.
> the horizontal part looks like a foot or two long, but it's difficult
> to judge from ground level, some distance away, These things are
> fitted in pairs, pointing in opposite directions, and are fitted a few
> metres from where the conductors are attached to the insulator strings
> at each tower. There is usually one pair on each conductor on each
> side of each tower, but occasionally a second or even third pair can
> be found, at roughly equal spacings. They look almost like small
> radio dipoles, but that wouldn't make any sense. Does anybody know
> what they are?

They are called Stockbridge Dampers.

The ones you saw are a horizontal tube which is a weight,
which is attached to a sprung metal support bar which runs
through the hollow and attaches to the tube at the far
end. The sprung metal support bar is clamped on the cable.
A google search turns up a nice picture halfway down
this article, although the construction is not clear:
http://www.theharrowgroup.com/artic...13/20020513.htm
This was the classic design, but there are other designs to
be found now, including simple spirals around the cable end
as can be seen in a picture I took some time back when I
first saw them: http://www.cucumber.demon.co.uk/lights/pole.jpg

Dampers prevent vibration traveling up the cable and putting
excessive stress on the insulator and supports. Vibration
comes from wind passing over the cable, and also if the cable
ices up in freezing rain or snow, and large chunks of ice
break away and have an effect like someone plucking a
guitar string.

The distance from the insulator and the resonant frequency
of the damper are critical for proper protection of the
insulator and support structure.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

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