Experimental Study on the Effect of Soil Moisture Content on Critical Temperature Rise for Typical Cable Backfill Materials

The increased utilization of power grid requires operating power cables close to their thermal limit. Buried power cables in such condition experience thermal instability where thermal resistance increases as the moisture migrates away from the proximity of the cable forming a dry-out zone. While it is common to use a two-zone model to account for the dry-out zone in ampacity calculations, there is a limited number of studies on characterizing backfill materials for their critical temperature rise (Δθ
_x
), especially for crushed rock sands. In addition, dependency of the Δθ
_x
on moisture content is sometimes not acknowledged. This study measures the Δθ
_x
for three typical backfill materials and investigates the relationship between Δθ
_x
and moisture content. The results show that crushed rock sand has higher Δθ
_x
compared to natural sand. Overall, large range of Δθ
_x
was measured depending on moisture content and type of soil. Ampacity calculations with the established Δθ
_x
show that at low moisture content, the thermal resistivity of the soil has a higher influence on ampacity than Δθ
_x
. At relatively high moisture content, the Δθ
_x
becomes the predominant factor governing the overall ampacity.