Gas Insulated Substation in Nokesville

 Come to an information meeting tonight.

Thursday, July 10 at 6 - 8 PM
Marsteller Middle School
14000 Sudley Manor Dr. Bristow

Dominion Energy is planning an upgrade to the Vint Hill Substation in Nokesville, Virginia, to meet the growing energy demands of data centers in Prince William and Loudoun Counties and maintain compliance with federal reliability standards. The project will involve adding 500 kV equipment, including transformers and Gas Insulated Substation (GIS) technology, as well as new 230 kV infrastructure. The substation's footprint will be expanded on Dominion Energy-owned property in Nokesville, but no new permanent electrical easements are needed. Construction is expected to begin in Spring 2026.

Gas insulated substations use sulfur hexafluoride (SF6) which is the most potent greenhouse gas known to mankind. Over a 100-year period, SF₆ is 23,500 times more effective at trapping infrared radiation than an equivalent amount of carbon dioxide (CO₂). SF₆ is also a very stable chemical, with an atmospheric lifetime of greater than 1,000 years. As the gas is emitted through leak or accidental release, it accumulates in the atmosphere in an essentially undegraded state for many centuries. Thus, a relatively small amount of SF₆ can have a significant impact on global climate change.

All equipment eventually degrades or fails though the modern GIS systems are designed with safeguards from hard earned experience. Today, each compartment housing the live sections of the GIS system is gas tight, with respect to one another. This prevents a leak from emptying all modules at once and ensures that gas monitoring is independent so a leak can be quickly located. These safeguards are designed to minimize the damage when there is a problem with the Gas Insulated Substation. Ultimately a repair will have to be made, a component replaced, or a leak will result in an accidental release of SF₆ .

 It is reported that Dominion Energy has other GIS in Virginia. They have real benefits: In addition to protecting the system components from extreme heat and cold, GIS technology encloses the electrical components within a Faraday cage which shields the system from potential lightning strikes a protection that is growing more important in Virginia as our climate changes and storms increase in intensity. GIS is more desirable as the voltage requirements increase, and land becomes more valuable when data centers proliferate in an area. The footprint of a 765kV conventional substation is very large. The total space required for a GIS is roughly a tenth of that needed for a conventional AIS facility. While the conventional, AIS requires several feet of air insulation to isolate a conductor, SF₆ gas insulation only needs inches, allowing a GIS facility to fit into areas far smaller than that of a AIS facility. A GIS is mainly constructed where real estate space is expensive or scarce.

In North America, substations have predominantly been air-insulated (AIS). In 2023  AIS volumes outpaced GIS volume by nearly a 6:1 ratio. AIS has been favored due to its cost-effectiveness and straightforward installation, making it the preferred choice for numerous applications, as mentioned earlier. However, in this case, data centers are driving the need for a GIS system and all the rate payers will have to bear the additional cost and risk.

Because of the climate risks, there is a move away from sulfur hexafluoride emerging.  Europe is leading the transition with plans to ban SF₆  -based switchgear by 2032; the US is considering following suit- though California has already moved to put a ban in place.

Though Prince William County has a 2030 climate goal to cut greenhouse gas emissions to 50% of 2005 levels or 2.1 million metric tons CO2e (MMTCO2e). Our passion to approve every single data center project that comes before the board for rezoning, special use, or exceptions will ensure that the county can never achieve that goal. Randy Freed of the Sustainability Commission estimates that instead of emissions reducing between 2018-2030, emissions increase dramatically.