What do UnderGround Power Stations and Grandma Have in Common?

The first underground substation in the U.S. was built by Anaheim Public Utilities in 2006, and they are getting bigger, hence the joke. As Grandma used to say, “Sometimes you have to hug your enemies to know how big a hole to dig.” The same logic applies to burying substations. Utilities today aren’t digging graves for foes, but they are asking: How massive does the hole need to be? The answer? For projects like Eversource’s $1.5 billion Greater Cambridge Energy Program (GCEP), it’s 35,000 square feet—enough to fit three football fields—buried 105 feet underground.  Eversource is planning to build an underground substation in a vault located approximately 110 feet below the surface in Massachusetts. But size isn’t the only story. From weatherproofing megacities to hiding infrastructure beneath parks, underground substations are rewriting the rules of grid design. Let’s dig in.

What Does AI Say About Underground Substations?

Underground power substations, or underground vaults, are electrical facilities beneath the surface. They distribute electricity from power plants or high-voltage sources to homes and businesses, offering advantages like reduced visibility and accident risk. Underground substations play a crucial role in the electricity distribution system by transforming high-voltage electricity into lower voltages suitable for homes and businesses. They are typically found in urban and suburban areas where overhead lines would be impractical. They are buried several feet below ground and connected to the distribution system via cables.

• Distribution Substations - These substations are designed to lower the voltage from the transmission system and distribute it to end-users, such as homes and businesses.

• Transmission Substations - These substations establish connections between two or more transmission lines, often near significant power sources or where electricity leaves the transmission network for distribution.

• Mining Substations - Underground substations are also essential in mining operations. They provide reliable power networks that support every facet of mining processes, from machinery to safety systems.

Grid Stability: Underground’s Secret Superpower

Underground substations significantly enhance grid stability by mitigating weather-related vulnerabilities and integrating advanced technologies for real-time power management. Buried infrastructure is inherently shielded from extreme weather events, such as hurricanes and ice storms, which frequently disrupt overhead systems. For instance, during back-to-back storms in Florida, areas with underground systems experienced minimal outages compared to overhead networks, underscoring their resilience. This protection ensures continuous operation during black-sky days, reducing downtime risks by up to 85% and avoiding costly economic losses - estimated at $2 billion per day in storm recovery for utilities like Florida Power & Light.  

Additionally, underground substations facilitate seamless integration of renewable energy and storage systems, which are critical for balancing variable solar and wind generation. Projects like Eversource’s Greater Cambridge Energy Program employ 115 kV transmission lines and gas-insulated transformers to manage power flow efficiently, while real-time monitoring systems optimize grid responsiveness. By embedding energy storage near substations, these systems act as "shock absorbers," stabilizing demand spikes and enabling rapid recovery during outages.

Top 10 Reasons to Use Underground Substations

1. Space Efficiency - Underground substations occupy minimal surface area, freeing up valuable land for other uses such as parks, buildings, or community spaces. For example, Eversource's Greater Cambridge Energy Program integrates a substation beneath a green space, demonstrating how underground designs optimize urban real estate.

2. Enhanced Grid Reliability - Underground substations significantly reduce outages and ensure continuous power delivery by shielding them from external environmental hazards like storms and falling debris. This resilience is especially critical in disaster-prone areas.

3. Improved Security - Subterranean placement makes substations harder to access, protecting them from vandalism, sabotage, or theft. Advanced security systems such as biometric access controls and surveillance further enhance their safety.

4. Reduced Noise Pollution - Underground substations naturally dampen operational noise from transformers and switchgear. This makes them ideal for residential or urban areas where maintaining quiet environments is essential.

5. Visual Appeal - By eliminating unsightly overhead lines and bulky surface structures, underground substations improve the aesthetic of neighborhoods and city centers. They contribute to unobstructed skylines and cleaner urban landscapes, increasing community acceptance.

6. Weather Resilience - Underground facilities are protected from extreme weather conditions, such as hurricanes, tornadoes, and ice storms, ensuring uninterrupted operations during adverse events.

7. Environmental Benefits - Underground power substations offer significant environmental benefits by reducing land clearing, preserving green spaces and wildlife habitats, minimizing visual pollution, and lowering risks to birds and wildfires compared to above-ground installations.

8. Support for Renewable Energy - Underground substations are equipped to efficiently integrate renewable energy sources like solar and wind power into the grid. Their proximity to urban load centers facilitates clean energy distribution.

9. Long-Term Cost Savings - Although initial installation costs are higher, underground substations save money over time through reduced maintenance needs, lower transmission losses, and improved efficiency in densely populated areas.

10. Community Integration - Underground substations can be seamlessly incorporated into urban environments by being placed beneath parks, malls, or public squares. This dual-purpose approach fosters community acceptance while meeting energy demands.

Underground substations represent a forward-thinking solution for modern energy infrastructure, simultaneously addressing space constraints, reliability concerns, aesthetic challenges, and environmental impacts.

Underground Security: James Bond-Proof Infrastructure

Post-9/11, the U.S. Federal Energy Regulatory Commission (FERC) mandated physical safeguards for critical nodes secured and monitored to thwart physical and cyberattacks. Modern underground facilities employ multi-layered security systems aligned with NERC CIP-014 standards, combining perimeter electric fencing, infrared surveillance, and AI-driven analytics to detect real-time anomalies. For example, thermal cameras and volumetric detection systems provide 360° monitoring, while redundant communication networks ensure that alerts persist during outages. Additionally, burying communication conduits in concrete and dispersing critical infrastructure across multiple smaller substations complicates large-scale attacks, forcing adversaries to breach numerous secure sites simultaneously. These strategies comply with federal regulations and exemplify how spatial concealment and technological integration create a robust defense-in-depth framework.

Underground substations significantly enhance security against attacks and sabotage by minimizing physical exposure and integrating advanced protective measures. By burying up to 98% of infrastructure below ground, these facilities drastically reduce visibility and accessibility to critical equipment, deterring opportunistic and coordinated threats. Underground substations are inherently more secure and harder to target due to several design features:

1. Concealment - Up to 98% of the substation volume can be placed below ground, making critical infrastructure virtually invisible and inaccessible to potential attackers. This dramatically reduces the visual and physical target area compared to traditional above-ground substations.

2. Limited Access Points - Underground facilities have fewer entry points, which can be more easily monitored and secured. This contrasts with above-ground substations, which may have multiple vulnerable areas along their perimeter.

3. Hardened Structures - Underground substations are often housed in reinforced concrete structures, which provide natural protection against ballistic attacks, vehicular ramming, and other physical threats.

4. Compact Design - Modern underground substations utilize gas-insulated switchgear (GIS) and other compact technologies, reducing the overall footprint and concentrating critical equipment in smaller, more easily secured areas.

5. Integrated Security Systems - The enclosed nature of underground substations allows for the comprehensive integration of security measures such as biometric access controls, motion sensors, and infrared surveillance systems throughout the facility.

6. Distributed Infrastructure - Some utilities opt to build multiple smaller underground substations instead of fewer large ones, making coordinated attacks more difficult and improving overall grid resilience.

7. Environmental Shielding - Being underground naturally protects equipment from extreme weather events, electromagnetic pulses, and other environmental hazards that attackers could exploit.

8. Reduced Electromagnetic Signatures - The earth surrounding underground substations helps contain electromagnetic emissions, making it harder for attackers to detect and locate critical equipment using specialized sensors.

By combining these design elements, underground substations present a significantly hardened target compared to traditional above-ground facilities, enhancing both the physical security and operational resilience of critical power infrastructure.

Underground Gets Hot, Let’s Keep It Cool

Underground substations require advanced thermal management systems to counteract heat buildup in confined, low-airflow environments. Unlike above-ground facilities, they lack natural ventilation, making passive cooling ineffective. 

High-Frequency Switching (HFS) technology operates at elevated frequencies to reduce transformer size and heat generation. HFS minimizes eddy current losses and enhances thermal dissipation, making it ideal for compact underground environments where cooling is challenging. HFS reduces transformer size by up to 60% by operating at higher frequencies, lowering eddy current losses and improving thermal dissipation in compact spaces. However, this generates higher temperatures, which require the other system components to be adapted to the application and support higher tolerances. One of the other new components is solid-state transferomers (SST), based on silicon carbide (SiC) models. These components are paired with capacitors designed for high-temperature operation, often using high-temperature and high-energy storage film dielectrics to handle reactive power demands without degradation. These high-temperature components enable underground substations to operate reliably under challenging thermal conditions while maintaining efficiency and safety.

Peak NanoPlex Goes Underground

Like most digital elements in the modern power grid, underground substations require capacitors with higher temperature tolerances to support the grid, keep things stable and cool, and reduce maintenance. By leveraging these advancements, power distribution systems can become more efficient, reliable, and capable of meeting the growing demands of our increasingly electrified world. Advanced capacitor technologies, such as those developed by Peak, offer promising solutions to current challenges:

• Higher Energy Density: NanoPlex HDC films can store 2-4 times more energy, allowing for more compact and efficient capacitor designs.

• Reduced Size and Weight: These advanced films enable two-times smaller and lighter capacitors, facilitating easier installation and reducing infrastructure requirements.

• Improved Durability: NanoPlex LDF provides 3-5 times longer lifetimes and duty cycles, addressing the need for more reliable and long-lasting components in power systems.

• Enhanced Temperature Tolerance: With support for temperatures up to 130°C, these new capacitor films can better withstand the harsh conditions often encountered in power distribution environments.

50% of New Substations Go Underground by 2040

Currently, underground substations are not the rule, with only a few fully underground facilities operating globally. In the United States, the first fully underground substation is being constructed in Cambridge, Massachusetts, as part of Eversource’s $1.8 billion Greater Cambridge Energy Program. This substation will occupy 35,000 square feet and be buried 105 feet below ground, marking a significant milestone in underground power infrastructure development.

The adoption of underground substations is expected to grow significantly over time. Utility companies are increasingly recognizing the benefits of underground designs, including space efficiency, resilience against extreme weather, enhanced security, and improved aesthetics. By 2040, approximately 50% of new distribution systems will be underground. Urbanization pressures drive this shift, and as the need for reliable power infrastructure and ambitious electrification goals tied to renewable energy integration, as cities like Cambridge demonstrate the feasibility and advantages of underground substations, more utilities and governments are likely to invest in similar projects to modernize their grids while addressing environmental and community concerns.