The invention relates to a method for diagnosing the state of an asynchronous motor (M) to which three-phase voltages UR, S, T (t) having a supply frequency (fU) are applied, comprising the following steps: a) detecting a
voltage time sequence (Ut) of the voltages UR, S, T (t) and a
current time sequence (It) of three-phase motor currents IR, S, T (t) flowing through the asynchronous motor (M) as a result of the voltages UR, S, T (t) applied to the asynchronous motor (M); b) calculating a
current spectrum I (f, t) and a
voltage spectrum U (f, t) on the basis of the detected
time series (It, Ut) by means of FFT; c) calculating one or more of the following time-dependent spectral variables 1-6: 1) the current components Ia (f, t), Ib (f, t), where Ia (f, t) and Ib (f, t) are formed from IR, S, T by Park transformation; 2)
total current amplitude AI (f, t) = square root of (Ia (f, t)) 2 + (Ib (f, t)) 2); 3) the
phase angle phi ab (f, t) between the current components is equal to arctan (Ia / Ib); 4) the
phase angle phi UI (f, t) between the current and
voltage components = arctan (U (f, t) / I (f, t)); 5) instantaneous spectrum power P (f, t) = U (f, t) * I (f, t); 6)
admittance X (f, t) = I (f, t) / U (f, t), d) is a spectral variable calculated for anomaly analysis; and e) reporting the exception when the exception is confirmed.