| 摘要 |
PROBLEM TO BE SOLVED: To properly detect higher harmonic waves properly, even if the rate of voltage peak value of higher harmonic waves to fundamental waves is small at several %, by detecting the higher harmonic waves of power system voltage in such condition that they are resonated and enlarged, with a means for detecting the voltage being divided at the specified ratio in a specified impedance section. SOLUTION: A series circuit consisting of a specified impedance 372 section and a capacitor 373 is connected to the circuit, thus a resonance circuit with the higher harmonic frequency of power system voltage is constituted. Then, in case that the peak value of the higher harmonic voltage existing in the power system is smaller than that of the fundamental wave, the ratio of the side of the specified impedance is set to be higher, out of the ratio of the impedance by the capacitor 373 to the specified impedance 372. Hereby, the higher harmonic waves can be detected with high sensitiveness, by raising the resonance enlargement ratio, and dividing it again so that it may be the maximum rated value or under of the input signal level of an A/D converter 371, at the specified impedance 372 section. |
