H-structure, Ductile Poles, Pupi Arms and Braces...Alternatives?

[apMechE]

Rebuilding some 69kV T line in some rolling hills where I am forced to replicate what is there today, H-structures with 600-800' spans. I have recently spec'd ductile poles with Pupi fiberglass crossarms (2 arms, currently spec'ing a single arm), braces, and cross brace arrangement. Curious what others have done? Looking to optimize this design to utilize the right combination for cost and longevity. Is it wise to keep all members fiberglass? Is the UV protection there to ensure a life expectancy of 60 yrs+? Will wood cross braces perform the same and save some cost? For additional strength on in-line deadends has anyone utilized steel even though it doesn't improve the BIL rating? Open to what others have done...

 

[FPelec]

Interesting question: given the prices I observe in my geographical area, if the required conductor has a relatively small diameter, for a 66 kV line, it might be cost-effective to use lattice or tubular steel supports (with steel crossarms and glass insulators or, alternatively, insulating crossarms).

As an example, a tubular steel pole for a straight-line span of approximately 800 feet (250 m), suitable for supporting a 1/2-inch diameter ACSR conductor (ACSR 12.7 mm), weighs about 3,800 pounds (1,750 kg). Under the same conditions, a lattice steel support would weigh around 1,250 kg.

With a lattice or tubular support, you would have a much smaller right-of-way, lower environmental impact and vegetation management costs, and likely lower foundation costs compared to an "H structure" solution. However, I believe the situation could be very different if very inexpensive wooden supports were available. Is that the case?

Aside from that, I would personally be cautious about the long-term durability and maintenance of fiberglass structural elements, especially over a 50-year depreciation period, which is typical for power lines.