Mott MacDonald provided engineering and detail design services to Klondyke Construction for the interconnection of the three solar plant blocks to the southern California Edison substation about 4m away. Our role involved the detail design of three separate circuits consisting of a combination of underground and overhead 115KV transmission lines. The overhead transmission consisted of 795ACSR conductors and the underground transmission consisted of 1,250KCML solid dielectric cable.
Key services
- Detail design and engineering
- Structure specifications, loading diagrams and outline drawings
- Design of steel pole structures in a double circuit vertical configuration
- Cable route and cable plans, splice location plan, grounding for the underground direct buried in a trench backfilled with thermal sand
- Design for riser station for transition from underground cable to overhead line
Challenges
- Cable ampacity calculation and selection of the appropriate thermal backfill
- Design of 39 structures, typically 70ft tall with several angled structures
- Design of riser stations with cable terminations in fenced in areas
- Final dead-end structures to be located outside one of southern California Edison’s future switchyards
- Review and approval by client’s engineers
- Approval of drawings and calculations by authorities
Solutions
- We collaborated with the cable supplier to generate cable ampacity calculations and cable installation configurations. Transmission lines were modelled using PLS-CADD software and we provided plan and profile design drawings.
- Foundations were designed using PLS-Caisson software.
- Tangent structures were designed with direct buried poles in the fenced in areas.
- Strong interface and coordination with Southern California Edison on the dead-end structures. The angle and dead-end structures were constructed on augured cast-in-place concrete foundations varying in size from 4-6ft in diameter and up to 19ft deep.