| 摘要 |
PURPOSE:To extract even sub-integer order higher harmonic components as well as integer order higher harmonic components positively by determining Fourier coefficients through discrete approximation while employing values contained in two periods of basic wave obtained by sampling output waveform of current flowing into a shunt of higher harmonic filter while equally dividing one period of basic wave into 2K sections. CONSTITUTION:Current is shunted from a higher harmonic filter circuit 1 through a CT and auxiliary converted 11 to produce a voltage which is then subjected to sample & hold 12, multiplexing 13, performing A/D conversion 14 and stored 21 over a predetermined cycle. Effective value 22 of all higher harmonics and an effective value 24 determined through Fourier operation 23 are subjected to subtraction 25 and level decision 27, and a relay 28 is actuated when the duration in which the level is higher than a predetermined one exceeds a time limit 26. Fourier operation is carried such that one period of basic wave is equally divided by 2K and the basic wave for two periods is taken out from sampled values in order to determine sine and cosine components of n/2-th order thus determining an effective value. Since higher harmonics shunting a higher harmonic filter facility can be caught surely, a highly reliable relay can be obtained. |
