Strained conductors

[Danilo917]

Good Day!

just want to ask information regarding strained overhead conductor..if the ratio of adjacent spans is 1:2,should straining of conductors (i.e ACSR & AAAC) required?what are other criteria involved in straining a conductor? Appreciate posting any reference materials for this subject.

thanks for your time and info in advance

Regards,

Danilo

 

[bacon4life]

By straining are you referring to the difference between dead-end insulators and suspension insulators? I have not heard your terminology used before.

A difference of that much does violate typical ruling span assumptions and can result in more sag in the longer spans that calculated using a RS assumption, significantly higher tensions in the sorter spans and longitudinal loads on the structures. The impact also depends on the flexibility of your structure and insulator.

 

[Danilo917]

Good Day!

strain structure is actually a type of pole construction where you install an insulator,bow/thimbl on pole to strain the conductors at both sides to certain tension.

we normally do this for an angle pole that exceeds max angle that pin construction is restricted to perform.

what im inquiring is about other criteria or rule of thumb that warrants the straining of conductor,say, is a 1:2 ratio of adjacent spans automatically requires conductor to be strained?what particular deviation in vertical spans or elevation are needed to make a strain pole construction?

regards

 

[Marmite]

It's not possible to answer this question without reference to the specification your line was built to. I would draw your attention to that specification. There isn't a generic answer.
Regards
Marmite

 

[bacon4life]

Spans with different attachment elevations should be checked for longitudinal loads from offset clipping and for uplift effects at very cold temperatures. Also, the higher pole will be carrying more of the conductor weight. This analysis could indicate that shorter spans, stronger poles, or deadend poles are needed, but I have not heard of elevation differences in general as a criterion for installing strain/deadend connections instead of tangent connections.

One thing to keep in mind is the difference between strain hardware attaching the conductor to a tangent pole and having a dead end pole strong enough to withstand the full tension of conductors on just one side.

Some of the things to consider when deciding where to put a deadend pole with strain hardware:
Line angle change.
Locations for all of the pulling equipment at the end of each reel of conductor.
Changes in grade of construction where increasing to a more reliable grade of construction at freeway, railroad or river crossings.
Some types of tangent construction are subject to cascading outages, so deadend structures can be installed to limit the cascading to just a manageable number of tangent structures.
Construction sequencing requirements. Sometimes deadends are added to allow construction of smaller portions of a line to be done independently.

We use strain hardware connected to a tangent strength pole in a number of other locations:
Changes in conductor types but similar weights.
Poles with air break disconnects
Clearance problems where changing from a suspension insulator to a set of strain insulators raised the conductor the needed 3 ft.
A bird problem where ospreys were living on a tower above some suspension insulators. As the birds took off their droppings would short across the vertical insulator. Changing the insulators from vertical to horizontal eliminated the problem.
Locations where isolation may be needed by opening a jumper, such a tap to an industrial load.

Our older lines have more strain connections than would appear in a new design. As changes were made to the system there were reasons to add extra strain connections, but very rarely an immediate reason to remove obsolete ones.