please can someone work me through

[bukky333]

please can someone work me through this question: utility is looking to replace a 138kv,LPFF underground cable installed in 1955. The circuit has been very reliable until past few year. The circuit experience 4 failures in 3 years. Analysis of the failure has determined that corrosion and fatigue of the sheath is the root cause of the failures.
The current circuit is 2 miles in length installed in a manhole conduit system. The conduit is 5" in diameter and the manholes are about 20 feet long. The current 138kv cable is 2250kcmil, copper conductor, lead sheath no jacket with a diameter of 3.25".
the utility is looking for a solution to increase the reliability of the circuit since the circuit is a transmission power path.

for cable design: determine conductor material and size
shield jacket
insulation thickness
sheath type and thickness
jacket type and thickness
overall diameter of the cable

I am proposing to change the existing cable from 2250KCMIL LPFF cable to 3000kcmil HPLPP cable.

does anyone know how to calculate above for 3000kcmil HPLPP cable or anyone that does similar design that can work me through?

thank you.

 

[Artisi]

This is either a homework problem or you're not a student.
A cable manufacturer would be a good place to start.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)