Design of an Induction Generator with Copper Squirrel Cage Rotor and Asymetric Slots

The operation of the induction machine as a generator is widely employed by generation systems based on wind power, hydropower, biomass and biofuels. However, the machine takes its excitation from external source of reactive power, which can mean that the induction generator is an inherently low power factor machine. This paper investigates a 2.2-kW three-phase induction machine designed to operate exclusively as a generator in parallel with the grid, i.e. driven above the synchronous speed. The objective is to obtain higher values of power factor and efficiency than those observed in a conventional squirrel cage machine developed as a motor but operating as a generator. Under these conditions, two induction machines with same frame, stators and rated data are modeled by means of the finite element method. Both machines have squirrel cage rotors. The first is an off-the-shelf one with the original aluminum cage and designed to operate under motor mode; the second one has a rotor designed to allow the machine to operate as a generator with a copper cage and asymmetric slots on the rotor. The theoretical results provided by finite element simulation performed on the machines are presented and compared to show the differences in performance of both those machines that favors the performance of the designed induction generator.