To obtain a measuring method in which the influence of a noise is excluded and in which a harmonics characteristic can be measured with good accuracy by a method wherein the voltage and the current, of a noise existing in a power system, at respective frequencies are subtracted and corrected from a voltage and a current at respective intermediate harmnics in the power system measured by injecting currents at the respective intermdiate harmonics.
A current injection device 3 repeats, at every 30 minutes, an operation in which a current at an intermediate harmnics is generated so as to be injected into an injection point (a). The infected current in the injection point (a) is measured by a current transformer 4. The voltage of a power system 1 is measured by a transformer 5, and a current on the side of a load in the injection point (a) of the system 1 is measured by a current transformer 6. Then, the analog measured output of the current transformer 4, that of the current transformer 6 and that of the transformer 5 are converted into digital signals by an A/D converter 7 in a harmonics measuring apparatus so as to be supplied to a signal processor 8. The processor 8 analyzes digital frequencies of the measured outputs by the current transformers 4, 6 and the transformer 5 so as to detect the voltage and the current of the system 1. In addition, the analyzed result of the processor 8 is supplied to a processor module 9. The processor module 9 subtracts the vector of a noise, and it computes a harmonics characteristic.
TSUKAMOTO MASAKAZU
NISHIMURA SOJI
NATSUDA YASUKAZU
NISSIN ELECTRIC CO LTD
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