A Power System Reliability Framework Considering Soil Drying-Out Effect on Underground Cables

New cable installations are used to expand the power network's transmission capacity. Considering only fundamental cable design aspects and very conservative ratings can often lead to incorrect network reliability assessments while limiting asset's capacity and network transmission flexibility. Additional cable design aspects should be considered to improve network modeling with underground cables and utilize their thermal inertia contribution toward network flexibility and reliability. This work advances existing long-term network planning tools by aggregating cables’ rating model, soil drying-out properties, and a novel cable high-loading risk model into a Sequential Monte-Carlo method. These modeling additions allow the design of indices that quantify cables’ thermal inertia and thermal aging risks. Consequently, the proposed methodology can help utilities quantify benefits and costs from improved design measures to mitigate soil drying-out and identify appropriate backfill materials depending on a cost-benefit analysis. A modified IEEE 14-bus network is used to quantify the risks of soil drying-out effects on operational network security and the benefits of utilizing emergency rating as a flexibility measure. Results show emergency ratings could reduce EENS by ≈90%. However, increased cable aging risk is expected under unfavorable drying-out soil conditions. This is significantly reduced with the use of backfill materials.