Special problem arising from the unique characteristics of the ultrahigh-speed induction generator applied in a system developed to generate electric power by utilizing waste and/or renewable energy sources. The studied system is built up from a high-speed turbine coupled to a three-phase induction generator, an AC/AC converter and a supervisory control unit. The purpose of the system is to utilize the energy content of a working medium by the help of a special high-speed turbine converting the energy content of the medium into electric energy with a generator and an AC/AC converter. Many different energy sources can be used with the application of the system, e.g. the energy resulting from the process of pressure reduction in steam, gas or fluid networks. The generated electric power can be fed to the utility mains or it can be used in standalone mode. The special properties of the system are studied only in respect of the unusual behavior of the ultrahigh-speed induction generator.