Electric generators are described herein. The electric generators include an interior machine formed of an interior rotor and an interior portion of a stator, and an exterior machine substantially concentric to the interior machine. The exterior machine includes: an exterior rotor substantially concentric to the interior rotor, and an exterior portion of the stator. Each of the interior machine and the external machine are driven by an engine to produce a respective current. The described electric generators can be used in diesel electric locomotives.

A method for manufacturing a main rotor for a generator is provided. The method includes printing at least part of a rotor shaft by a three-dimensional printing process. The step of printing at least part of the rotor shaft includes printing a plurality of closed outlets and a plurality of open outlets. A rotor core is printed by the three-dimensional printing process. The step of printing the rotor core includes printing a plurality of liquid coolant conduits that extend through the rotor core and fluidly connecting the plurality of liquid coolant conduits to the plurality of closed openings.

A method for manufacturing a main rotor for a generator is provided. The method includes printing at least part of a rotor shaft by a three-dimensional printing process. The step of printing at least part of the rotor shaft includes printing a plurality of closed outlets and a plurality of open outlets. A rotor core is printed by the three-dimensional printing process. The step of printing the rotor core includes printing a plurality of liquid coolant conduits that extend through the rotor core and fluidly connecting the plurality of liquid coolant conduits to the plurality of closed openings.