Uplift on tower with suspension insulators

[nitin36537]

Does it effect when Tower location is such that Back weight span is 400 m and Ahead weight span is -300m .

So under normal condition total weight span 400-300 = 100 m ( Total weight of wire action down ward) But under broken wire condition when back side break tower is under weight span of -300 m.

Weight of wire is 1.5 kg/m . So uplift load will be 1.5 * -300 = -450 kg (upward)

Foundation has enough strength to withstand addition uplift load due to -300m span.

Even cross arms of tower are safe with uplift from -300m span.

I am proposing to add counter weights on insulators of say 600 kg. (600-450 = 150kg downward load under broken wire condition also .)

Is this sufficient ?? Or ...I am missing somethig??I am not sure about Insulators. Insulators used are V type suspension.

Is there any good books which discussed such types of problems??


Thanks

Nitin Patel

 

[MikeDB]

I suggest you look at RUS Bulletin 1724E-200. It is available for free download at

http://www.usda.gov/rus/electric/bulletins.htm

If I understand your situation, you should be looking into insulator swing. If that is not a problem for the horizontal and vertical spans on the structure, then don't add weights.
If you have a broken conductor, that is a different load case, which creates a longitudinal load on the insulators and the structure. Adding weights will not help that situation.
Mike

 

[nitin36537]

Thanks Mr MikeDB for replay.

I had also asked this to PLS CADD , I got replay as under from PLS CADD

Calculations of broken conductor loads have quite a lot of subjective judgment and experience based rules. Firstly, the dynamic loads involved are ignored or converted to pseudo static loads for design of towers in order to prevent cascading failures, so excessive accuracy may not be arranted in such calculations.

Regarding negative weight spans, I would like to remind you that the weight spans you get with intact conductors would be different if you break the conductor on one side of the tower because of the movement of the insulator string and the reduction in the tension. With the Finite Element module in PLS-CADD (SAPS plug-in), the new weight span and conductor tensions can be accurately calculated for static residual loads. If your tower is modeled with either PLS-POLE of TOWER software, you can run the structural analysis of this tower in PLS-CADD and check its adequacy with the calculated weight spans and conductor tensions, all internally done in PLS-CADD. If the structural software confirms that your tower is adequate, you should not
need to add any counter weights.

You need also to check the ability of the V string to rotate and become almost horizontal under your case of broken conductor, assuming little or slightly negative weight spans. Depending on the design of attachment point,
you may end up with a localized torsional moment that might reduce the capacity of the crossarm.