Cast Resin vs Oil Filled MV Transformer

[FaradayFF]

Hi All,
I'm looking to spec out a medium voltage, 3MVA, outdoor located transformer. I'm considering cast resin transformer or a standard pad mount, environ oil filled transformer. This would be stepping down from 25kV to 4.16kV.
What are some of the advantages and disadvantages of using padmount versus cast resin(cast coil) type? Would cast resin would be typically more expensive albeit a more environmentally friendly option?
Thank you,
DD

 

[Joethemechanic]

Yeah well my thought is what works for low voltage, dosen't scale for medium voltage well.

No convective cooling currents like oil. And if there is a insulation degradation, there is no fixing it. Becomes a big deal with a 3MVA trans with the transport , crane rentals, and the rigging. And not to mention the foundation (pad) will probably need repair, modification, or replacement

 

[D. Castor]

Cast coil unit will likely be considerably more expensive than a standard outdoor oil-filled unit. Advantages of cast-coil: can be indoor or outdoor, highly resistant to contamination or corrosion, no oil leak/spill concerns. We used these for industrial facilities with corrosive environments and where indoor units were desired or required. No transformer vault is required and can be close-coupled to the switchgear.

If this is a typical commercial or light industrial application, probably oil-filled outdoor pad-mount would be the least costly. But that will be a big 480 V feeder to bring into the switchgear.

Delivery time could be an issue as well.