CONTROLLED BACKFILL OPTIMIZATION TO ACHIEVE HIGH AMPACITIES ON TRANSMISSION CABLES

The earth thermal resistance is the largest resistance to heat dissipa tion for underground cables, and is' by far the most variable of the r esistances. Accurate knowledge of this resistance, and its modificatio n, can provide substantial ampacity increases, with confidence that th e cables will remain within allowable operating temperatures for all d esigned loading conditions. This paper provides background on the hist ory and present use of controlled backfill, the effect on cable ampaci ties, and procedures for optimizing the amount of controlled backfill based upon cable installation conditions, including native soil therma l resistivity. Backfill optimization for a specific pipe-type cable ci rcuit with high ampacity requirements is reviewed, and installation pr ocedures are described.