500KVA tranformer in manhole

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Ithinkimstillhere

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I need to provide a 500KVA dry type transformer within a manhole. The dimension of the hole is 10'x12'x12'. It will have a sump pump and a drainage inlet.I was thinking about providing a steel grate for ventilation, but how do I elevate the pad in the case of flooding (failed sump)? It needs to be elevated at least 2 to 3 feet I think. This transformer will only be active roughly 3 days out the year for a fourth of July events. Should I order the contractor to provide a steel grate AND a solid liquid tight cover for when the transformer isn't in use?
 
What are the voltages involved and where are the loads (are you doing the distribution after the transformer)? Is the manhole under cover/inside a building or out in the open? Assuming it's LV, even though 500kva isn't small, for that short usage period it might be much more economical to set a watertight jbox for the high side and make the rest of the installation temporary (or to use more smaller transformers around your site). If you have to go below grade, you will have water and failed pumps. There might be freeze damage. You'll also have core losses all year long unless you de-energize between use, and if you do that, you have the potential of humidity and water damage to the core. Is a dry-type transformer even rated for that location? I think you'll need a real underground distribution transformer.

(yet again, I'm posting before I've finished my coffee)
 
If and only if flooding the transformer is not an issue then my concern would be ventilation. Since a transformer does generate heat are you going to provide provisions to ventilate the heat? Then, to deal with humidity ventilation is also important. A transformer that is energized should not be subject to damaged winding because of humidity. A deenergized transformer is at risk for damaged windings as a result of moisture condensation.
Again, ventilation is important as it should keep the air moving which reduces the chance of moisture condensing. As such it is very important to assure the the transformer include space heaters that would be energized when the transformer wasn't
If you have these items addressed I see no issues to what you're proposing.
 
templdl said:
If and only if flooding the transformer is not an issue then my concern would be ventilation. Since a transformer does generate heat are you going to provide provisions to ventilate the heat? Then, to deal with humidity ventilation is also important. A transformer that is energized should not be subject to damaged winding because of humidity. A deenergized transformer is at risk for damaged windings as a result of moisture condensation.
Again, ventilation is important as it should keep the air moving which reduces the chance of moisture condensing. As such it is very important to assure the the transformer include space heaters that would be energized when the transformer wasn't
If you have these items addressed I see no issues to what you're proposing.
Click to expand...
In addition, you can also consider a TENV silicon encapsulated transformer that are NEMA 3R. There are not designed to be submergible but the windings are enpasulated. These transformers are comonly available up to 250kva 1ph, 500kva 3ph.
 
templdl said:
In addition, you can also consider a TENV silicon encapsulated transformer that are NEMA 3R. There are not designed to be submergible but the windings are enpasulated. These transformers are comonly available up to 250kva 1ph, 500kva 3ph.
Click to expand...

Another choice might be a cast coil transformer. The enclosure and bussing might not survive too many floods, but the coils themselves are very impervious. Although 500kVA may be too small.
 
jim dungar said:
Another choice might be a cast coil transformer. The enclosure and bussing might not survive too many floods, but the coils themselves are very impervious. Although 500kVA may be too small.
Click to expand...

I was going to include a cast coil as an option but thought that it was a little too pricey. The company that I once worked for imported the component cast coils from Germany and then assembled them on their cores bus assemblies etc.
 
I would shy away from this setup if at all possible. I installed several 7200 to 120/240 transformers in bathtub vaults for a local park for 2 to 3 events throughout the year. They were designed or submersion yet became problematic after 3 years. We ended up replacing them with pad mounts.
 
I would shy away from this setup if at all possible. I installed several 7200 to 120/240 transformers in bathtub vaults for a local park for 2 to 3 events throughout the year. They were designed for submersion yet became problematic after 3 years. We ended up replacing them with pad mounts.
 
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