Influence of harmonic voltage distortion on asynchronous generators

Renewable and dispersed electrical generators can be divided into systems directly coupled to the grid, or systems which use power electronic converters for grid connection. A lot of generation is still done by an induction machine directly coupled to the grid, for example in micro combined heat power or small wind turbines. For asynchronous generators directly coupled to the grid, the voltage distortion can have a significant influence on the efficiency of the machine. A lot of papers discuss the influence of voltage harmonics on Induction Machines. The influence of voltage harmonics on Induction Generators is less researched. Although some research has been performed through simulation, due to difficult laboratory setup not many practical efficiency measurements have been performed on Direct On Line Induction Generators for a medium power range. This paper discusses the practical test setup and measurement results for two different 55kW Induction Generators fed by a programmable power supply. Specifically the influence of the phase angle of the harmonic on the overall efficiency is tested.