Theoretical analysis has revealed that considerable impact can be found on the operation of ultra high speed machines, caused by subharmonic components [1,2]. The system studied is applied to generate electric power by utilizing renewable energy resources. The results obtained by numerical calculations were confirmed by computer simulations and also by laboratory tests. The low level of subharmonics, superimposed on the fundamental and high frequency components poses a challenge for reliable laboratory measurement; furthermore the large amount of test data makes the process of evaluation laborious. The paper presents a test method developed for the measurement of subharmonic components in a fast and automated way by applying a test arrangement and a computer program developed for the analysis of the test data. The basic idea of the method is described in the paper presenting examples of test results obtained by the method described and comparison is made with the results of corresponding numerical calculations.