Apparatus for detecting abnormal conditions of transmitted signals

In apparatus for detecting an abnormal condition of a transmitted signal of the class wherein a carrier wave frequency modulated by an electric quantity is transmitted to a receiving station and the frequency variation of the carrier wave is detected by an abnormal condition detector installed in said receiving station so as to detect an abnormal condition of the transmitted signal, the improvement wherein some abnormal condition detector comprises means responsive to the received carrier wave for alternately producing positive and negative waves in alternate periods of the received carrier wave, an integrator for integrating the output from said means, a comparator responsive to the output of said integrator for producing the difference between the widths of said positive and negative waves, and a one-shot multivibrator responsive to the output of said means for producing an initial point setting pulse applied to said integrator and a judging pulse applied to said integrator and said comparator.

In a protective relaying system of a transmission line interconnecting first and second electric stations of the type wherein a carrier wave frequency modulated by an electric quantity of said first station is transmitted to said second electric station for operating a relay installed therein, the improvement which comprises an abnormal condition detector provided in said second station and including means for comparing the lengths of contiguous or closely adjacent periods of the received carrier wave, and means responsive to the output of said comparing means for controlling said relay.

In a protective relaying system of a transmission line interconnecting first and second electric stations of the type wherein a carrier wave frequency modulated by an electric quantity of said first station is transmitted to said second electric station for operating a relay installed therein, the improvement which comprises an abnormal condition detector provided in said second station and including means responsive to the received carrier wave for alternately producing positive and negative waves in alternate periods of the received carrier wave, an integrator for integrating the output from said means, a comparator responsive to the output of said integrator for producing the difference between the widths of said positive and negative waves, a one-shot multivibrator responsive to the output of said means for producing an initial point setting pulse applied to said integrator and a judging pulse applied to said integrator and said comparator, and means responsive to the output of said comparator for controlling said relay.