Preparing for the next big earthquake is a way of life for many Californians, and Pacific Gas and Electric Co. (PG&E) is no different. The utility serves a seismically active area in northern and central California, so designing and reinforcing its electric and gas systems to better withstand significant shaking is a big priority.
PG&E is in the midst of an important transmission and substation project that will harden the system serving San Francisco in the event of a catastrophic earthquake. The company is building a new 230-kV power line under the San Francisco Bay and two new gas-insulated substations in the city to add greater redundancy and resiliency for natural disasters.
In the event of a significant seismic activity or emergency situation, the new power line will serve as an additional source of energy to prevent a power outage. In addition, the upgrades will increase capacity and improve the reliability of the electric service to the about 29,000 customers in downtown San Francisco and the surrounding areas.
“The new power line and substations will provide an additional source of reliable electricity for San Francisco residents and businesses to meet growing demand and enhance readiness in the downtown area when a catastrophic emergency occurs,” says Gregg Lemler, PG&E’s vice president of electric transmission operations. “Every day we’re working to build a stronger and more resilient system for our customers.”
Installing an Underwater Line
The project reached an important milestone in July when PG&E successfully submerged the underwater portion of the new power line in the San Francisco Bay. This was a significant engineering achievement that required extensive planning and coordination.
PG&E used a barge to stage a 350-ton reel of cable seismically and specially designed for an underwater environment. As the cable was unspooled off the barge, divers guided it into bay-to-land transition conduits, and a hydro-plow laid it into a trench on the bay floor. Three of these cable reels were needed to complete the approximately 2.5-mile underwater portion of the line.
The utility installed the underwater line between 6 ft to 10 ft below the floor of the bay, and then plans to install the remaining portion below city streets in San Francisco. By going through the bay, PG&E has been able to minimize disruption to San Francisco’s busy Financial District. Going through city streets to connect the cable between PG&E’s existing Potrero and Embarcadero substations would have required building 25 vaults across 45 blocks of city streets. By going through the bay, however, PG&E only needed to construct two vaults.
Overall, the new power line will stretch 3.5 miles between two new gas-insulated substations adjacent to PG&E’s existing Potrero and Embarcadero substations in San Francisco. The portions of the line on land will be buried underground in a trench designed to allow the cable to flex and move during an earthquake.
Construction of two new gas-insulated substations is also under way. These facilities will use inert gas contained within metallic piping that will help protect equipment such as circuit breakers, switches and transformers when a catastrophic earthquake strikes.
The new substation expansions will be enclosed to provide a more aesthetically pleasing environment for the community.
PG&E began planning the project in 2011 with work starting in September 2014. The new line is scheduled to be in service by the end of 2016. This project is part of a five-year PG&E plan to invest $1.2 billion in San Francisco’s electric and gas infrastructure to provide safe and reliable service for customers. John Parks, senior director of transmission projects, says the project is incredibly important for PG&E and the city of San Francisco.
“The Embarcadero substation serves about 40,000 customers with about half a million people working in the city’s Financial District each day,” Parks says. “With the growing demand in this area, the project will provide expanded capacity and capability.”
The utility’s investments throughout its entire service area in northern and central California have resulted in record electric reliability for six straight years. Since 2009, PG&E has consistently reduced the average duration of power outages, and in 2014, the utility’s customers experienced the fewest number of outages in PG&E’s history.
Brian Swanson ([email protected]) is a communications principal for Pacific Gas & Electric.