Angle Suspension or Strain Arrangement?

[StrTLE]

Hi
I am working on this line realignment project where an angle suspension tower is used as terminal structure outside of Sub-station.
Please see the attached pdf document for the questions. Any help is appreciated.

Thank you.

 

[bacon4life]

Why do you propose converting to a strain arrangement? Using deadend insulators will increase the loading on the tower under most loading situations. If the drop to the substation is a short span with a large elevation change, the differential tension could be substantial under extreme conductor temperatures.

Structural analysis doesn't necessarily mean a full blown computerized PLS-Tower model. You may be able to demonstrate that the new loads are less than the original design loads using a simple paper & pencil loading diagram. It would be irresponsible to reconfigure a transmission tower without a reasonable level of structural analysis.

 

[bhyde]

I agree with bacon4life. If the substation deadend does not require some other tension than what is out there now, I see no need in deadending the new alignment. It will cause more loading issues and should be analyzed structurally then.

If you are simply re-aligning the conductors (i.e. no new conductor installed), you should see lower loadings than the current configuration. The only question I would have is if you have enough clearance to the tower with the new alignment...

 

[StrTLE]

Thank you bacon4life and bhyde for the responses.

I was thinking of line/substation reliability and the structure design philosophy. If this tower or any of its components experienced a failure then it could affect the substation taking it out of service. I thought having a strain structure if required with guy wires to balance longitudinal tension from line side. Guying will put additional vertical loads on cross-arms requiring strengthening, however it will increase reliability of the line. Do you guys agree with my thoughts?

I agree structural analysis doesn't have to be PLS-Tower analysis. A simple head load check is good. Structure loads with re-configured suspension arrangement will be less than the existing suspension arrangement due to reduced line angle and no change in conductor tension.
I was trying to ask the line reliability issue above if it can be explained in few words to the client.

Clearances are not a problem with re-configured suspension arrangement.

Thank you.

 

[bacon4life]

Guy wires attached typical lattice towers are unlikely to work well. In order for a guy wire to pick up much load, the attachment point has to deflect a significant distance. The deflection in an unguyed lattice tower under full design load is going to be less than a few inches. The deflection in an unguyed wood or steel pole under full design load could easily be a couple of feet. The tension in a guy wire attached to a lattice tower will probably depend more on ambient temperature than on the structural loading of the tower. (Note that guyed lattice towers do exist, but they are a completely different design. They have a pivot point at the bottom to allow the entire tower to deflect or rotate under load).

If the tower under consideration experiences a failure, I don't see how the insulator attachment type will protect the substation equipment. If you are referring to failures further down the transmission line cascading towards you substation, reframing it as a deadend won't help unless you specifically design it as a weak link. Only if the tower were actually a full tension deadend could it measurable improve reliability. However, since this seems to be a tangent tower, reframing as a deadend would not add reliability. I think the deadend hardware and splices would actually result in a marginally less reliable configuration.