METHOD FOR DETECTING BROKEN RODS IN A SHORT-CLOSED ROTOR WINDING OF ASYNCHRONOUS ELECTRIC MOTOR Russian patent published in 2023 - IPC G01R31/34 

FIELD: electrical engineering.

SUBSTANCE: invention relates to the field of monitoring the technical condition of asynchronous electric motors and may be used to detect broken rods in the short-circuited winding of the rotors of asynchronous electric motors. Essence: register the stator current when starting an asynchronous motor. The digitized signal is divided into intervals of duration ΔT satisfying the condition

where ΔF is the relative width of the main lobe of the window used compared to the width of the main lobe of the rectangular window; T_n - starting time of the asynchronous motor, s; f_c - frequency of the supply voltage, Hz. The frequency-time spectrum of the registered signal is formed using the Short Time Fourier Transformation. Then the presence in the spectrum of a harmonic component from the fictitious winding of the rotor at the lower side frequency is determined, the order of which coincides with the number of pole pairs of the induction motor. A conclusion about the presence of broken rods in the rotor winding is issued. When such harmonic component is detected, the asynchronous motor is connected to the frequency converter. A mathematical model of the induction motor start-up process is preliminarily formed. The mathematical model is used to determine at f_c equal to 50 Hz, the range of voltage values U_calc at the output of the frequency converter, satisfying the condition U_calc.min<U_calc<U_calc.max, where U_calc.min is the minimum effective voltage value at which the motor can start, V; U_calc.max - the maximum effective voltage value at which the start time will be more than 0.8 s, V. U_start is chosen from the range of U_calc. The output voltage of the frequency converter is set to U_start and the frequency of the output voltage is set to 50 Hz. The start of an asynchronous motor is carried out through a frequency converter.

EFFECT: increased reliability of detection of broken rods in the short-circuited winding of the rotors of asynchronous electric motors with a start duration of less than 0.8 seconds.

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