| 摘要 |
PURPOSE:To realize positive protection by selecting three sample values, separated by a predetermined value from each other, from sample values obtained by equally dividing one period of an objective wave and then determining an effective value based on these three sample values according to a specific formula, thereafter comparing thus determined effective value with a reference value. CONSTITUTION:An AC filter 22 comprising a capacitor C passing a specific higher harmonic, a reactor L, and a resistor R is connected between a distribution line 21 and the ground and then the filter current is detected through a CT 23. Thus detected current is fed to 5 digital protective relay 1 for AC filter facility and then it is subjected to step-down through an auxiliary transformer 11, attenuation 12, S/H 13, A/D conversion 14 and stored in a memory 15. Three sample values im-p, im, im+p (m=0, 1, 2...), separated by predetermined number P corresponding to the order of higher harmonic, are then selected and subjected to operation at a first operating section 16 to determine Lm, whereas an effective value is determined at second operating section 17 and compared 18 with a reference value. If the effective value is higher than the reference value, a protective signal is outputted, According to the constitution, basic wave component is blocked positively resulting in suppression of the generation of aging or temperature variation. |
