This paper compares the accuracy of the multi-frequency stator phase current spectrum estimation. This is as a development of considerations made in . In this paper, the authors added to previous results for the classic Discrete Fourier Transform method and the two-point interpolated DFT method (IpDFT ), new results obtained by three-point IpDFT method’s algorithm. The analysis was made for slip spectrum component which is used for cage damage detection. To minimize the spectrum leakage effect, the selected Rife-Vincent Class I windows (RVCI ) were used. The article focuses on the effectiveness of spectral component estimation in function of the used method, type of time window and measurement time. Values of errors of frequency and amplitude estimations are presented on graphs. The authors compared theoretical considerations with the case of real stator current of an asynchronous motor with a broken cage. This article can be used as a base for further studies on the diagnosis of induction motors.