Oil containment pit for outdoor transformer - Less-flammable oil (FR3) vs mineral oil

[JADEN98]

Hi. I have been asked to design a foundation and oil containment pit for an outdoor transformer in a substation. The insulating oil (FR3) in the transformer has a high flash point (~330 C) and is self-extinguishing and non-propagating. I wonder if there is still a need for the pit to be filled with quenching rock as is the case with the mineral oil. The problem is that I cannot find any clause in NFPA 850 or IEEE 980 that explicitly waives this requirement for this type of oil. Since the substation is in a rainy area, omitting the crushed rock layer would result in a much smaller foundation, otherwise deep foundation is inevitable as the surface area of the pit cannot be extended any further. I wonder if some of the colleagues have the experience of designing the containment pit for this kind of oil, and if anyone knows of any code clause that could be referenced to remove the crushed rock layer?

 

[stevenal]

My copy of 980 speaks of risk and probability (7.1.1.4). I see nothing here that would prevent an engineer from assigning low risk to a less flammable fluid. Can you control touch and step potential without insulating stone and meet IEEE 80?

 

[dik]

I've often used a product called Sorbweb that eliminates the need for a containment. The 'basin' is filled with clean stone with an impervious liner with an opening covered in Sorbweb material. During normal operation rainwater can flow throught the opening, but in the event of a transformer leak, the soil causes the Sorbweb to gel to prevent contamination of the groundwater. The company is Albarrie (sp?) and they have been involved in half a dozen transformer yards that I've been involved with. They're excellent. (I have no connection with the company)

https://albarrie.com/products/oil-blocker-plus-oil-spill-containment-systems/

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[JADEN98]

Thank you @dik for your suggestion. In fact, my initial concept was using a Sorbweb "window" to deal with the rain issue but the client vetoed it on the spot. But even with Sorbweb, would you omit the crushed rock layer when the oil is less-flammable? I mean there is a clear difference in the risk imposed on the fire safety which might be taken into consideration in the design process.

 

[JADEN98]

Thank you @stevenal for your reply. The grounding design meets the requirements of IEEE 80 as is according to the electrical engineer, and he doesn't seem to be willing to make any input on the issue of fire safety for less-flammable oil which is why I am trying to find anything in the literature or existing facilities that would get us out of this deadlock.

 

[dik]

Sorry to hear that... my experience with Sorbweb has been excellent and generally much less costly than the alternative of using a concrete structure that requires draining and filtering. I was curious about the first time I used it... and beyond that, my experience has been really good. I wouldn't consider using containment without it. I did a huge containment for six 400,000Kip transformers on a slab supported by helical piles in Saskatchewan and the piles were designed so that 10' beneath the slab could be excavated to replace the damaged aggregate in the event of a leak. If memory serves, the cooling oil for each transformer was equivalent to two rail tanker cars... a lot of 'juice'. I seem to recall designing the containment for 1-1/2 transformer 'leaks'. 10 years back and I don't recall the details...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dik]

I don't think the flammability has any bearing on the stone... do you have to construct 'blast' walls?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[JADEN98]

No. All the code clearances have been met in the layout of the substation and as such firewall is not necessary. Had it been that the oil containment was to be designed for multiple transformers, the argument for not designing for the total volume of all transformers would have been perfectly valid and well-referenced. Unfortunately, I am dealing with one transformer and so the whole volume must be considered in the design plus precipitation and freeboard.

 

[stevenal]

Is 100% containment required in your jurisdiction? I understand the EPA treats in-use oil differently than stored oil, and one is allowed to consider the largest creditable release. I believe one could consider the release from the bottom of a radiator to come up with a number somewhat less than 100%.

 

[rambopg]

I have a similar issue for a US project. It's not a substation and the transformer is only 1500kVA (with FR3 oil). The transformer will be installed on a concrete pedestal beside a modular E-house. From my initial research it doesn't require an oil containment concrete pit. For such a small transformer if the oil spills, do bio-remediation.

https://www.cargill.com/doc/1432160810652/w1030-remediation-oil-is-not-oil.pdf