An electric utility in California needed to expand a substation in an urban neighborhood. The station was originally built in 1918, with later upgrades in the 1940s. Growing power demand in the community and the increased risk of wildfires meant the 138/12kV AIS substation and its transmission infrastructure needed to be upgraded.

The challenge was that the existing substation was on a footprint that was too small to accommodate the expansion using a traditional air-insulated substation. The site also contained the original utility building at the front of the property—a historic landmark which the community wanted preserved and restored. The utility chose to replace the existing air-insulated substation with a pair of 230/138kV and 138/12kV gas-insulated switchgear (GIS) substations. Using GIS reduces substation footprints by as much as 80–90% and, in this case, meant the utility could preserve the historic building and complete the needed grid resiliency project within the existing site.

Even though GIS technology has existed for several decades, it is still a relatively new and innovative technology for most utilities. Only about 5% of new substation construction in the U.S. utilizes GIS. On this utility’s grid, this substation project was only the third GIS site.

Minimizing Community Impact

Leveraging a GIS approach meant the project could expand to the needed 230kV capacity with minimal impact on the surrounding community. Phased construction and strategic cutover sequences minimized outage time for the nearby community and reduced the strain of construction outages on the region’s grid.

Throughout the project Beta Engineering and the utility scheduled deliveries during off-peak hours to reduce or eliminate traffic congestion and timed loud construction activities to minimize noise disruptions for the surrounding area. These measures limited the project’s impact on the area, which included not just the neighbors across the street, but also the nearby historic downtown district and several schools.

Solving Challenges

In addition to the challenges of the small footprint and congested residential location, the project also involved crossing over a major interstate and under an active railroad line as well as complex cable pulling into the 138kV GIS building.

• Highway Crossing: Beta worked with the state highway patrol to coordinate traffic breaks for stringing four distribution circuits across the freeway. The crews performed most of their work early in the mornings to reduce impact on traffic. The team also installed temporary poles and strung netting across the freeway below the proposed conductor routes to ensure no live lines could fall to the road below.
• Railroad Crossing: Installing conductor below the railroad involved extensive coordination with the railway to facilitate safe jack and bore construction. Railroad flagmen provided supervision during all construction activity, which enabled the crew to work safely without the railway having to take any outages. Throughout the process, the track was closely monitored and surveyed to ensure it was not impacted by any of the drilling so the trains could continue to operate safely.
• Cable Pulling: Due to space constraints, the cable into the 138kV GIS building could not be pulled using conventional methods. The project team solved this challenge by creating and executing a complex crane and pulley system that fed the cable through windows installed near the top of the building’s west side.