V String Insulators 1

[StrTLE]

Hi

On a current project we are proposing V-string insulators for 500kV suspensions and angle suspension structures. my question is will V-string insulators always take tension in all loading conditions avoiding compression completely? If there is compression in one of the two V-string insulators how much compression is allowable?

also guide if it is ok to use V-string insulators on 15 deg angle suspension structures?

Thanks in advance.

 

[MikeDB]

I think you will always want some tension in each leg of the V string to minimize TV and Radio interference and to reduce wear. Most suspension insulators, like a rope, don't do well in compression.

The maximum line angle will be a function of the vertical load, the horizontal load and the angle of the V string, such that the insulators remain in tension. Most of the line angle structures use a different V-string configuration to facilitate this.

 

[StrTLE]

Thanks MikeDB for the answer.

my consideration is also the same, i.e. V-strings to always have tension. we are adjusting the weight spans to account for this. however, i am not sure if this actually holds true for all loading conditions (wind, ice, etc).

I don't understand about the TV and radio interference.

we are using different included angle between the V-strings for angle suspensions. but is stringing the conductor for these structures an issue? we are going to check with the contractor about this. my point is that the conductor is to be strung through the rolling block on these structures and it being a 15 deg deviation; is that going to be a relatively easy task? has anyone found any issues related to stringing with these type of structures with V-strings? i dont want to proceed too far and then contractor finds difficulties during stringing.

Thanks for the help.

 

[transmissiontowers]

On the TV interference, I am a structural and understand a little electrical stuff that I've picked up after 38 years at a utility. When the compression side of a V-string unloads when the wind blows and the line angle pulls, the gaps that result in the porcelain bells or the links in the polymer start to crackle and emit RF. It was much more apparent in the days of AM radio when you drove under a T-Line and the radio did nothing but buzz.

We only go up to 345kV, so 500 may be different, but you can lower the attachment point of the outside V-String insulator or raise the point of the inside so when you swing through 15°, the compression side stays with some tension.

If you consider that you want both insulators in tension under most load cases, it depends on your location. For places with lots of ice and not much wind, it is not too hard to keep both loaded. In my area on the Texas gulf coast where 140 mph wind can occur, you can't always count on both insulators being loaded all the time.

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

 

[JWKilgore73]

Some utilities vary the insulator angles. I'm working with a utility right now that uses 45/45 degrees for tangent towers and 45/70 for angle towers between 6 and 22 deg. Anything over that gets a dead-end.

If the weight span is too small they add weights to the attachment (up to a few thousand pounds) to force the inside string into tension. No hurricanes here, but they are designed for "microburst" horizontal winds at 20psf.