An electric generator includes a process gas inlet on a downstream side of the flow control valve to receive process gas into the electric machine; a rotor shaft including a node position, the node position defining a position of a node of a first bending mode of the rotor shaft; a turbine wheel coupled to the rotor shaft at the node position, the turbine wheel configured to receive process gas and rotate in response to expansion of the process gas flowing into an inlet of the turbine wheel and out of the outlet of the turbine wheel, the rotor shaft configured to rotate with the turbine wheel, and a stationary stator, the electric generator to generate an alternating current upon rotation of the rotor within the stator. The turbine wheel selected from a plurality of turbine wheels based on the operational conditions of the electric generator.