Controlled backfill optimization to achieve high ampacities on transmission cables

The earth thermal resistance is the largest resistance to heat dissipation for underground cables, and is by far the most variable of the resistances. Accurate knowledge of this resistance, and its modification, can provide substantial ampacity increases, with confidence that the cables will remain within allowable operating temperatures for all designed loading conditions. This paper provides background on the history and present use of controlled backfill, the effect on cable ampacities, and procedures for optimizing the amount of controlled backfill based upon cable installation conditions, including native soil thermal resistivity. Backfill optimization for a specific pipe-type cable circuit with high ampacity requirements is reviewed, and installation procedures are described