What Size Transformer Oil Containment System Do I Need?
- By Dan Carver
- Dec 6, 2023
Secondary containment around oil-filled transformers plays a vital role in preventing environmental damage caused by leaks or spills. These systems act as a protective barrier, capturing oil before it can reach the soil or groundwater, especially in substation environments where large volumes of oil are stored.
The EPA’s Spill Prevention, Control, and Countermeasure (SPCC) Rule outlines the requirements for oil-filled equipment like transformers. Facilities with an aggregate oil storage capacity of 1,320 gallons or more are required to implement either secondary containment or maintain a certified Oil Spill Contingency Plan (OSCP). For transformers, this means designing a containment system capable of holding 100% of the volume of the largest transformer, plus an additional 10% to allow for precipitation or snowmelt.
Transformer leaks are often caused by faulty gaskets, deteriorating radiators, or corrosion in the tank structure. Even with consistent maintenance, these components can degrade over time, making containment an essential safeguard. It ensures regulatory compliance and helps utilities avoid costly cleanup efforts and environmental penalties.
How does this apply in practice when calculating secondary containment for transformers? Read on to learn more.
Calculating Transformer Oil Containment
While calculating the total volume of oil is a critical first step to understanding the containment capacity required for your transformer, it's only one of several factors that impact the design of your substation's secondary containment system. Other important considerations include:
- Number of vessels on site
- Total amount of oil on site
- Site topography
- Physical encumbrances on the site
- Buildings, pilings, piers, cable runs
- Fences, roads, gates
- Depth of the grounding grids
- Size and depth of pads
- Available footprint
Meet SPCC Regulations for Transformer Oil Containment in 6 Simple Steps
At BCI, we make it easy for engineers to figure out what size transformer oil containment is necessary to meet SPCC regulations. You can calculate the secondary containment volume requirement for your transformer area by following these six steps:
Key:
1 cubic foot = 7.50 gallons of capacity
1 cubic foot of stone = 3 gallons of capacity at 40 percent void
- Identify the oil volume of the largest transformer within the containment area. Add 10% to this volume to account for freeboard—extra space for rain or snow accumulation.
- Determine the depth of your transformer containment area. Base this on the current depth of stone and your site's layout. Then, calculate the oil-holding capacity per square foot. Keep in mind that different stone sizes have different void spaces, which affect this calculation.
- Divide the 110% containment volume by the per-square-foot capacity of the stone. This gives you the total square footage needed for oil containment.
- Calculate the square footage of the transformer pad and any additional piers within the containment area.
- Add the square footage of required containment (Step 3) to the square footage of pads and piers (Step 4). This gives you the total area your transformer oil containment system needs to cover.
- Determine the dimensions of the sidewalls. Use the total square footage and factor in site-specific constraints—such as fencing, existing infrastructure, and layout—to finalize the containment design.
Calculating Transformer Oil Containment: A Case Study
To meet SPCC compliance, an electric utility plans to install secondary containment for a 600-gallon transformer mounted on an 8-foot by 10-foot concrete pad. A fence line is located 30 feet away from one side of the transformer. Using the six-step method outlined above, here’s how to calculate the necessary oil containment volume:
- Determine the required oil containment volume: 600 gallons × 1.1 (to include 10% freeboard) = 660 gallons
- Assess stone depth and void space: The site has 12 inches of stone with 40% void space, giving a containment capacity of 3 gallons per square foot.
- Calculate the area needed for oil containment: 660 gallons ÷ 3 gallons/sq ft = 220 square feet
- Measure the area of the transformer pad: 8 ft × 10 ft = 80 square feet
- Add containment area and pad area: 220 sq ft + 80 sq ft = 300 square feet total area needed
- Determine final containment dimensions: To keep the system symmetrical within the 30-ft fence line, a width of 13 feet (6.5 feet on either side of the pad) and a length of 24 feet would yield 312 square feet, which exceeds the required 300 square feet—ensuring compliant and practical transformer oil containment.
SPCC Regulations
- Standards for Electric Utility Companies
- Regulatory Codes that Apply to Construction Activities
- Tips for Complying with SPCC Regulations
Types of Transformer Oil Containment Systems
BCI offers engineered, site-specific oil containment solutions designed to meet regulatory requirements and adapt to varying soil conditions.
Barrier Boom Secondary Oil Containment
Ideal for sites with clay or other impervious subsoils, this proven system allows rainwater and snowmelt to drain normally during typical weather conditions. However, in the event of a transformer oil spill, the Barrier Boom immediately acts as an impermeable barrier to hydrocarbons, preventing environmental contamination.
Geomembrane Liner System with Barrier Boom
This system is compatible with all subsoil types and is particularly effective for containment pits installed directly around the transformer rather than along the full substation perimeter. It combines the durability of a geomembrane liner with the protective performance of the Barrier Boom for targeted secondary containment.
Contact Us Today for More Info About Transformer Oil Containment
Over 10,000 substations worldwide rely on BCI oil containment systems. Contact us today for proven secondary containment solutions.
Secondary oil containment around transformers is critical for capturing oil spills and protecting the environment. SPCC regulations provide guidance for containing oil-filled equipment. The rule specifies sizing oil containment systems to contain the contents of the largest vessel - or in this case, the transformer inside the containment area. Add 10 percent to the volume of oil to accommodate precipitation or snow.
How does this work practically for calculating secondary containment for transformers?
Calculating Transformer Oil Containment
Though calculating the required oil containment capacity for your substation is important, the total volume of oil is just one of many factors that influence the design of your secondary containment system. Additional considerations include:
- Number of vessels on site
- Total amount oil on site
- Site topography
- Physical encumbrances on the site
- Buildings, pilings, piers, cable runs
- Fences, roads, gates
- Depth of the grounding grids
- Size and depth of pads
- Available footprint
Meet SPCC Regulations for Oil Containment in 6 Simple Steps
We make it easy for engineers to figure out what size transformer oil containment is necessary to meet SPCC regulations. Calculate the secondary containment volume requirement for your transformer area by following these six steps: Key: 1 cubic foot = 7.50 gallons of capacity 1 cubic foot of stone = 3 gallons of capacity at 40 percent void- Find out the volume of oil for the largest transformer vessel in the area that needs containment. Add 10 percent freeboard to account for rain and snow.
- Determine the depth of the secondary containment area based on existing stone depth and the site layout. Calculate the capacity of oil for one square foot surface area. Note that different stone sizes have different void space for capacity calculations.
- Divide the 110 percent volume required by the capacity per square foot of stone. This reveals the square foot area of oil containment required.
- Calculate the square foot area of the transformer pad, plus any other piers in the containment area.
- Add the square foot of containment required (Step 3) to the square foot of the pads (Step 4) to find the total square foot area.
- Determine the length and width of sidewalls based on this square foot area and the physical constraints and barriers of the site (such as fencing, etc.)
Calculating Transformer Oil Containment: A Case Study
To comply with SPCC regulations, an electric utility wants to install secondary containment around its 600-gallon transformer. It sits on an 8-ft. by 10-ft concrete pad. A fence line lies 30 feet from the side of the transformer. Let’s follow the six steps above to calculate its secondary containment volume requirement:- Oil containment volume needed = 600 gallons x 1.1 = 660 gallons.
- Existing stone depth is 12 inches. The stone has 40 percent void space, yielding a stone capacity of 3 gallons per square foot.
- Area of containment required = 660 / 3 = 220 square feet
- Area of transformer pad = 8 x 10 = 80 square feet
- Total area = 220 + 80 = 300 square feet
- To fit within the fence line in a symmetrical containment area, choose a width of 13 feet (6.5 feet in each direction). A length of 24 feet would provide a total area of 312 square feet to meet our oil containment needs.
- Standards for Electric Utility Companies
- Regulatory Codes that Apply to Construction Activities
- Tips for Complying with SPCC Regulations
