With the population growth in the city, Xcel Energy has faced the problem of how to increase distribution system capacity and reliability in the urban core, where available real estate is becoming rare. Xcel Energy's Downtown GIS Substation is on the edge of downtown Denver, surrounded by businesses and residences that make expansion impossible. Rather than build a new substation on a new plot of land, a six-phase construction plan was developed to incrementally transform the 115-kV three-position single bus into a new 115-kV gas-insulated substation (GIS) configured in a six-position ring bus. This increases system reliability and frees up space for a third medium-voltage metalclad switchgear and capacitor bank to serve future load.
Burns & McDonnell’s design included a 2.5-story precast concrete enclosure for the GIS, rerouting one of the three 115-kV underground transmission lines and converting one of the three 115-kV/13.8-kV transformers from the air insulated bus to the GIS. This work included assisting Xcel with the permitting and coordinating with the architectural design team on the interior space and façade.
The extreme site constraints and proximity to an existing enclosure housing the protective relaying for the substation required the use of more than 60 helical piles, instead of standard piers, to support the foundation because they can be drilled into the subsurface with no vibration disturbance.
Burns & McDonnell designed the protection and control schemes of the 115-kV transmission lines, high-voltage bus and breaker failure operation. Additionally, we are responsible for the design of the communication network expansion, assisting with major material procurement and providing construction support.
Planning and construction sequencing
Detailed engineering and architectural design
Indoor GIS with limited site space
Complex demolition and installation construction sequencing with minimal outages
Aesthetically pleasing architectural design for the high-traffic and population-dense area