Power reactor for energy transfer comprising - a shaped casing that sits upon a support structure and a fixed winding, suitable for being electrically connected to an electrical energy supply network, contained inside said shaped casing with which it is associated through support means, - wherein said shaped casing and said winding are arranged a first distance apart which is a function of the electrical current, of the inductance and/or of the geometry of said winding and is not less than a predetermined minimum value in order to make it possible to drain the energy losses created by the parasite currents generated by the magnetic flux produced by said winding and that engages said shaped casing, said first distance diverging towards said shaped casing from an upper end portion of said winding crossed by the flux lines of the magnetic field that link together with said winding, - wherein said shaped casing is made from a nonmagnetic metallic material, - wherein said winding is immersed in insulating oil contained inside said shaped casing and - wherein said shaped casing and said winding are arranged a second distance (d) apart, perpendicular to said first distance and calculated from the side surface of said winding towards said shaped casing, which has a predetermined minimum value to increase the drainage of said energy losses, said predetermined minimum value of said second distance (d) being a function of the electrical current, of the inductance and/or of the geometry of said winding and said predetermined minimum value of said second distance (d) being no greater than said predetermined minimum value of said first distance, and wherein said predetermined minimum value of said second distance (d) is reduced to 1/5 of said minimum value of said first distance. - a shaped casing that sits upon a support structure and a fixed winding, suitable for being electrically connected to an electrical energy supply network, contained inside said shaped casing with which it is associated through support means, - wherein said shaped casing and said winding are arranged a first distance apart which is a function of the electrical current, of the inductance and/or of the geometry of said winding and is not less than a predetermined minimum value in order to make it possible to drain the energy losses created by the parasite currents generated by the magnetic flux produced by said winding and that engages said shaped casing, said first distance diverging towards said shaped casing from an upper end portion of said winding crossed by the flux lines of the magnetic field that link together with said winding, - wherein said shaped casing is made from a nonmagnetic metallic material, - wherein said winding is immersed in insulating oil contained inside said shaped casing and - wherein said shaped casing and said winding are arranged a second distance (d) apart, perpendicular to said first distance and calculated from the side surface of said winding towards said shaped casing, which has a predetermined minimum value to increase the drainage of said energy losses, said predetermined minimum value of said second distance (d) being a function of the electrical current, of the inductance and/or of the geometry of said winding and said predetermined minimum value of said second distance (d) being no greater than said predetermined minimum value of said first distance, and wherein said predetermined minimum value of said second distance (d) is reduced to 1/5 of said minimum value of said first distance.