JPS576366A - Apparatur for detecting frequency - Google Patents

Abstract

PURPOSE:To make an ideal protective characteristic approximate to an antitiming characteristic by only one frequency relay, by using the integral quantity of deviation value between reference frequency and system frequency of input as an element for determination of action speed. CONSTITUTION:A zero cross point of voltage input of a system introduced from a transformer 16, is detected by a detecting circuit 17 and an interval of the zero cross point generating at every half cycle or one cycle, is counted by a counting circuit 18. On occasion of lowering the frequency of the input voltage below a constant frequency, the set value of deviation in accordance with the deviation value of reference frequency at every half cycle or one cycle is added by a integrator 22 and the last output is put out by a level detector 23 when said integrated quantity becomes larger than a constant value. Hereby, a rapid action speed is obtained because the more the deviation quantity is large, the more the addition quantity becomes large and conversely, a slow action speed is obtained when the variation rate of frequency is small.