FIELD: electricity.
SUBSTANCE: in order to determine the first harmonic F1 of industrial three-phase voltage signals of all three phases Ua, Ub, Uc are used by summing up their voltage values and computing a negative-sequence voltage Uo. From the negative-sequence voltage Uo the third harmonic voltage is defined by a filter for an industrial frequency U3. A frequency F3 for the third harmonic voltage of the industrial frequency U3 is determined and the frequency of the first harmonic is computed as F1=F3/3. The frequency determining method for three-phase voltage allows determining the frequency of three-phase voltage, which rotates motor rotors directly. At that, due to the usage of all three phases of the industrial frequency of 50 Hz and due to the usage of the third harmonic voltage, the accuracy of voltage measurement is increased. The disclosed method will be efficient always when the spectrum of three-phase voltage includes the third harmonic voltage.
EFFECT: improved determination accuracy of three-phase voltage frequency due to the usage of signals of all the three phases of industrial three-phase voltage to this end and the usage of the interfering third harmonic directly for frequency measurement.
4 dwg
