Hermetically sealed, non-venting electrical apparatus with dielectric fluid having defined chemical composition

An electrical transformer comprising:

• an expandable enclosure having upper and lower ends and an interior chamber of varying volume that is permanently sealed from the ambient environment, said enclosure having a plurality of flexible walls and an upper surface on said upper end of said enclosure;
• a core and coil assembly disposed in said interior chamber beneath said upper surface of said enclosure;
• dielectric coolant surrounding said core and coil assembly and completely filling said interior chamber for dissipating heat that is generated by said core and coil assembly when said transformer is energized;
• and
• a substantially vertical duct in said chamber for directing toward said upper surface of said enclosure dielectric coolant that has been heated by said core and coil assembly such that flow of said fluid comprises a vertical loop in which horizontal flow is minimized, said loop comprising an inner fluid passageway and an outer fluid passageway wherein said outer fluid passageway surrounds said inner fluid passageway and communicates with said inner fluid passageway at the top and bottom of said duct, said core and coil assembly being disposed within said inner fluid passageway.

An electrical transformer comprising:

• a noncylindrical enclosure having an interior chamber that is permanently sealed from the ambient environment, said chamber being polygonal in cross section and having a plurality of corners;
• wherein said enclosure includes a bottom, a top that is spaced apart from said bottom, and a plurality of sides extending between said bottom and said top, each of said sides being attached to two other sides along lines of intersection, said lines of intersection forming said corners of said interior chamber;
• a dielectric fluid wetting all interior surfaces of said enclosure;
• a transformer core and coil assembly disposed in said chamber and having an overall footprint;
• a substantially vertical duct in said chamber forming a substantially vertical inner fluid passageway and a substantially vertical outer fluid passageway that surrounds said inner fluid passageway and communicates with said inner fluid passageway at the top and bottom of said duct, said inner fluid passageway surrounding said core and coil assembly and directing dielectric fluid that becomes heated by said core and coil assembly toward said top of said enclosure.

An electrical transformer for use in an ambient environment comprising:

• a rectangular enclosure having a bottom, a top spaced apart from said bottom, and four sides extending between said bottom and said top, said enclosure being permanently sealed from the ambient environment and having an expandable interior chamber that expands to include a range of volumes that includes a first volume and a second volume that is at least 10% greater than said first volume, said interior chamber being divided into inner and outer substantially vertical flow passages, said outer flow passage surrounding said inner flow passage and communicates with said inner fluid passageway at the top and bottom of said duct;
• and
• a dielectric fluid having an absolute pressure less than one atmosphere completely filling said interior chamber;
• wherein a plurality of said sides are flexible and have a concave outer surface when said dielectric fluid has an absolute pressure less than one atmosphere.