There was performed the research of the compliance with electromagnetic compatibility rules requirements for technical equipment, installed at the variable speed of the proof-of-compliance test station for synchronous generators. Variable speed of the generator is provided by usage of asynchronous motor supplied via frequency converter. During the trials of the generator under load there is foreseen regeneration of the energy to the mains. Such ability is defined by usage of thyristor converter, operating as mains-controlled mode inverter connected to the generator via three-phase bridge rectifier. Thus the station is characterized with closed power circuit. During the trials the currents’ waveforms in the lines and separately at the input of the frequency converter and the output of the regenerative device were registered. There are given the results of experimentally received data processing of the currents character and waveform. The currents flow in the closed power circuit of synchronous generators test station. The research of frequency drive and DC drive joint influence on the current total harmonic distortion and the voltage consumed by the test station from the mains, confirmed that these values do not exceed the limits set by normative documents. There are given recommendations according to elimination of current total harmonic distortion at the input of frequency converter.